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The Human Red Blood Cell Proteome and Interactome

Steven R. Goodman*1, Anastasia Kurdia, Larry Ammann, David Kakhniashvili* and Ovidiu Daescu

^* Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, Texas 75080; Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390; Jonsson School of Engineering and Computer Science, University of Texas at Dallas, Richardson, Texas 75080; and Department of Mathematical Sciences, University of Texas at Dallas, Richardson, Texas 75080

¹ 2601 North Floyd Road, P.O. Box 830688, Richardson, TX 75083-0688. E-mail: sgoodmn{at}utdallas.edu

	Abstract

TOP Abstract Introduction A Status Report of... The Human RBC Interactome RBC Proteomics as it... The Altered Interactome in... Final Thoughts References

 
The red blood cell or erythrocyte is easily purified, readily available, and has a relatively simple structure. Therefore, it has become a very well studied cell in terms of protein composition and function. RBC proteomic studies performed over the last five years, by several laboratories, have identified 751 proteins within the human erythrocyte. As RBCs contain few internal structures, the proteome will contain far fewer proteins than nucleated cells. In this minireview, we summarize the current knowledge of the RBC proteome, discuss alterations in this partial proteome in varied human disease states, and demonstrate how in silico studies of the RBC interactome can lead to considerable insight into disease diagnosis, severity, and drug or gene therapy response. To make these latter points we focus on what is known concerning changes in the RBC proteome in Sickle Cell Disease.

Keywords: red blood cell, erythrocyte, proteomics, interactome, systems biology, Sickle Cell Disease

	Introduction

TOP Abstract Introduction A Status Report of... The Human RBC Interactome RBC Proteomics as it... The Altered Interactome in... Final Thoughts References

 
The red blood cell (RBC) or erythrocyte travels through our circulatory system for 120 days, during which time it must constantly change its shape from a biconcave disc of 8 µm diameter to a cigar shape able to traverse passage ways that narrow to 1 µm in diameter. A two dimensional meshwork of proteins called the spectrin membrane skeleton, found on the cytoplasmic surface of the plasma membrane, gives the RBC its properties of elasticity and flexibility that allows for the success of this journey (1–5). Defects in this membrane skeleton lead to misshapen and osmotically fragile RBCs (6–10).

This tortuous journey traveled by the erythrocyte is for the purpose of carrying oxygen from our lungs to cells, tissues and organs throughout the body; and returning carbon dioxide to our lungs. This essential RBC function is conducted by hemoglobin, the major protein constituent of the RBC cytosol. The erythrocyte is the simplest of human cells as it lacks internal organelles; lost during the process of erythropoiesis. The ease of obtaining blood, lack of internal organelles, and important physiologic function of the RBC has made it a major focus of biochemical study during the 20^th and 21^st century. As a result, we know the functions of erythrocyte proteins in greater detail than any other human cell type.

The simplicity of the human erythrocyte cell structure has also made it an optimal cell for proteomic study. While nucleated cells contain 20,000 to 30,000 proteins (11–14), RBCs which lack nuclei and other organelles contain far fewer. It is, therefore, the cell type where we are most likely to approach a complete proteome in the foreseeable future. This fact, along with the comprehensive current literature on RBC function, will allow us to soon understand the relationship of the erythrocyte proteome and interactome to RBC function. Further, we are beginning to understand how changes in the RBC proteome and interactome relate to erythrocyte disorders. The proteome and interactome of the normal and abnormal human erythrocyte is the subject of this mini review.

	A Status Report of the Human Erythrocyte Proteome

TOP Abstract Introduction A Status Report of... The Human RBC Interactome RBC Proteomics as it... The Altered Interactome in... Final Thoughts References

 
To understand the human erythrocyte proteome we would need to know the identity of every protein, their amino acid sequence and posttranslational modifications (PTMs), the number of copies of each protein per cell, and all of their interactions (the interactome). The use of modern mass spectrometry, with appropriate search algorithms and comprehensive human protein databases allows one to study the complete RBC proteome; by the process called proteomics.

Here we will discuss the identification of RBC proteins by modern mass spectrometry and database searching. The story behind this portion of RBC proteomic data has unfolded over the past five years and closely follows the technical advances in the proteomics field over this period of time. The first serious study of the RBC membrane’s proteome was performed by Low et al and published in 2002 (15). Their focus was on plasma membrane proteins and they used the classical approach of two dimensional IEF–SDS PAGE (2D electrophoresis), followed by silver staining, in gel trypsin digestion and MALDI TOF mass spectrometry. To avoid some of the problems related to using 2D gels for proteomic identification (problems with high and low MW proteins, proteins with high and low isoelectric points, and hydrophobic proteins), they also performed one dimensional SDS PAGE. By a combination of these techniques, Low et al (15) were able to identify 84 distinct RBC membrane proteins. While the one dimensional gels did allow them to identify some hydrophobic proteins (ex. sorbitol dehydrogenase and the glucose transporter) other major RBC transmembrane hydrophobic proteins were not detected (ex glycophorin A and C).

Our laboratory utilized classical techniques for RBC fractionation, in combination with a shotgun proteomic approach and tandem mass spectrometry, to identify 181 unique proteins in the erythrocyte membrane and cytosol (16).

In this study by Kakhniashvili et al, tryptic digests were prepared individually from intact cells (to identify surface exposed proteins), inside out spectrin depleted membrane vesicles (to identify proteins exposed on the cytoplasmic membrane surface) and a low ionic strength membrane extract (to identify spectrin and other components of the membrane skeleton) (16). Each tryptic digest was individually separated by reverse phase HPLC and analyzed by tandem mass spectrometry utilizing a ThermoFinnigen LCQ DECA XP Ion Trap mass spectrometer. We identified 91 unique membrane proteins. In addition we separated the cytosolic proteins, by gel filtration chromatography, into 21 fractions. Each fraction was digested with trypsin and analyzed by LC – MS/MS as described above. Again 91 unique cytosolic proteins were identified. Glyceraldhyde–3-P–dehydrogenase was placed in both the membrane and cytosolic lists, because of the high number of hits in both fractions. Therefore, the total number of proteins identified was 181 which was the most complete erythrocyte proteome list available in 2004 (16). In this study by Kakhiashvili et al not only were the glycophorin A and C identified in the membrane fraction, but also proteins that are present in just a few hundred copies per RBC (ex B-CAM) (16).

In both the Low et al (15) and Kakhniashvili et al (16) studies many proteasomal subunits were identified. As previous studies had claimed no proteasomal degradation of proteins in RBCs (17), it was possible that these proteins were coming from a small number of contaminating reticulocytes. However, we have recently demonstrated by confocal immuno-fluorescence and western blot analysis that proteasomal subunits and intact proteasomes do exist in mature RBCs (18). Therefore, proteomic studies have now led to an exciting question for future exploration: What is the physiologic function of RBC proteasomes?

Collectively Low et al (15) and Kakhniashvili et al (16) had identified over 200 unique proteins. Studies that followed over the next year included the use of trypsin associated with self assembled monolayers on gold to create an enzyme chip for digestion of RBC protein prior to MudPit (SCX coupled to RPHPLC) and tandem mass spectrometry (19); and the use of soft Immobiline gels instead of IPG strips for 2D Electrophoresis prior to MALDI TOF (20). The former study by Tyon et al identified 272 proteins, but only 30 by 2 or more unique peptides (19). The latter study by Bruschi et al allowed greater visualization of high molecular weight protein spots on 2D Gels (20). While both studies contributed valuable new technologies, for specialized situations, neither added significantly to the number of RBC proteins that had been identified by proteome technology by 2004.

The next substantive increase in the number of RBC proteins identified by proteomic technology came at the end of 2006 (21). Pasini et al, utilizing both an Applied Biosystem Quadropole TOF Q–STAR mass spectrometer and a Thermo Electron hybrid linear ion trap Fourier transform MS (LTQ–FT MS), were able to identify 314 RBC membrane proteins and 252 soluble proteins (21). While Pasini et al (21) were careful to optimize the extraction of membrane proteins, with combinations of ethanol and Na Carbonate, the major contributor to the substantial increase in protein identification was technological. Proteomic advances are closely tied to technologic advances in mass spectrometers and Pasini et al (21) were using instruments with extremely high sensitivity (LTQ–FTMS has 1 ppm accuracy) and very high mass accuracy (attamoles). The result was their identification of 566 unique RBC proteins.

By combining all of the proteomic data discussed in this section, and ignoring PTMs including proteolysis, we have created a comprehensive list of RBC proteins identified, by proteomic technology, to date (Table 1). As shown in Table 1, we now know the identity of 751 proteins through proteomic technology. We have a long way to go to identify all RBC proteins and to know their complete sequence, PTMs, and number of copies per RBC. But as will be discussed in the following section, we can begin to assemble a preliminary interactome from the currently known RBC protein composition.

	The Human RBC Interactome

TOP Abstract Introduction A Status Report of... The Human RBC Interactome RBC Proteomics as it... The Altered Interactome in... Final Thoughts References

 
To better understand how disease processes, such as sickle cell anemia, affect the functions of erythrocyte protein networks, it is important to examine the interrelationships that exist among these proteins. A first step in this approach is to extract protein interaction information from databases that are currently available, and to express this information as a network graph. Compilation of such information is far from complete, and the information that is available contains false positives (listed interactions that don’t really exist in a particular organism) and false negatives (existing interactions that have not been discovered). Nevertheless, significant progress has been made to extend and improve protein interaction databases, and to include in these databases measures of confidence for the interactions.

The preliminary human erythrocyte interactome network presented here was derived from protein interaction data obtained from the Unified Human Interactome (UniHI) (22). To reduce the likelihood of including false positives in these networks, we only included interactions among erythrocyte proteins that had a Spearman correlation of at least 0.3. The Spearman correlation reported by UniHI is derived from gene expression experiments and represents a measure of confidence for the interaction (23). We selected a lower bound of 0.3 to include an interaction in the network since that threshold represents the 60th percentile of all returned interaction correlations and hence gives moderately strong confidence that the interaction is not a false positive. The graphics were generated with R (24) and the igraph package (25).

The resulting protein-protein interaction (PPI) network is depicted in Figure 1a. The nodes of the network are gene ID’s of the erythrocyte proteins, and the connecting line segments represent interactions between the corresponding proteins. Some of the erythrocyte proteins have no interactions between them and any other erythrocyte proteins that satisfied the threshold for retention. These proteins are omitted on all but the last figure. The structure of the network is visibly irregular with sparsely connected subgraphs, densely connected subgraphs, several clusters containing only a few nodes, and one large cluster containing the majority of proteins. The boxed region in Figure 1a is expanded and displayed in Figure 1b. This region is defined by the proteasomal, chaperonin, and heat shock proteins along with their immediate neighbors in the network. We refer to this box as the Repair Or Destroy (ROD) Box.

The ROD box contains proteins that utilize the energy of ATP hydrolysis to fold nascent proteins or refold damaged proteins (heat shock proteins and chaperonins). As mature Red Blood Cells are thought not to synthesize nascent proteins only the latter function is relevant to this discussion. The ROD box also contains proteins involved in the proteasomal degradation of ubiquitinated proteins (ex proteasomal subunits). The recent demonstration, by our laboratory (18), that proteasomes are present in mature RBCs raises the important question of whether ubiquitin dependent proteolytic degradation exists in RBCs. As can be seen in the Figure 1B, the proteins involved in repair of damaged proteins or destruction of proteins beyond repair are interacting within the ROD Box.

	RBC Proteomics as it Relates to Human Disease

TOP Abstract Introduction A Status Report of... The Human RBC Interactome RBC Proteomics as it... The Altered Interactome in... Final Thoughts References

 
Protein profiling, where the protein content is compared in control and diseased tissue, has become a powerful tool for diagnosis and the identification of new therapeutic targets. Early proteomic protein profiling studies utilized image analysis software to compare protein stained two dimensional gels of disease versus control cells and tissues. An example of this approach can be found in the comparison of RBC membrane proteins where control subjects are compared to participants with type 2 diabetes (26). In this study by Jiang et al (26), they found 27 spots upregulated and 15 protein spots down regulated in RBC membranes from type 2 diabetes patients. Those proteins that demonstrated significant change were identified by ingel trypsin digestion followed by MALDI TOF Mass spectrometry. The lipid raft protein, flotilin 1, was increased 4.8 fold; syntaxin 1 C was decreased 8.3 fold; and arginase was upregulated by 37.2 fold. Jiang et al speculated that decreases in the target membrane fusion protein, syntaxin 1C, could lead to reduction in translocation of the Glut 4 glucose transporter to the RBC plasma membrane during erythropoesis in type 2 diabetes (26). Further they suggested that the large increase in arginase could down regulate nitric oxide (NO) production, by creating a competition for the L-arginine substrate with NO synthase.

While this approach of image analysis of protein stained two dimensional gel has been historically valuable, as exemplified above, it is limited by the fact that protein migration from gel to gel is not identical. As a result, the technique of two dimensional difference gel electrophoresis (2D DIGE) was developed (27). In this approach the proteins in two samples (diseased versus control) are first labeled with Cy3 and Cy5 fluorescent dyes (sometimes using a Cy 2 labeled reference standard), then combined prior to two dimensional electrophoresis. The two different dyes can then be detected and fluorescent intensities determined for Cy 3 and Cy 5 for every protein spot. This approach was used by our laboratory for performing protein profiling on RBC membranes derived from homozygous (SS) Sickle Cell Disease (SCD) patient versus control (AA) (28). From over 500 fluorescent protein spots we found 38 that demonstrated 2.5 fold increase in sickle cell RBC membranes and 11 protein spots that demonstrated 2.5 fold decrease in SS RBC membranes (28). We chose a 2.5 fold threshold because when comparing RBC membrane proteins between control subjects we found that 99.8% of all determined ratios were within a 2.5 fold difference from the expected value of 1.0. We identified 44 protein spots by trypsin in–gel digestion followed by nanoLC-MS/MS tandem mass spectrometry. These 44 identifications included 22 unique proteins with various PTMs (28). As shown in Table 2, the proteins that were changing fell into five protein groups. Three of these groups were related to the extreme oxidative stress observed in SS RBCs: Protein repair participants (heat shock 70 kDa protein isoforms, chaperonin containing TCP1 subunits and T-complex protein 1 delta); proteasome components (proteasome 26S ATPase subunit 6, proteasome alpha subunit 1 isoform 1 and proteasome beta 1 subunit); and scavengers of oxygen radicals (catalase, peroxiredoxin 1 and peroxiredoxin 3 isoform a) (28). All of these proteins, except one (chaperonin subunit zeta 1), were increased greater than or equal to 2.5 fold in sickle cell RBC membranes. This demonstrates that the RBC and its erythropoetic precursors are launching an adaptive response against the elevated levels of oxygen radicals and diminished reduced glutathione found within SS RBCs (28). The two major lipid raft components in RBCs, flotilin 1 and stomatin, had four different protein spots all diminished in SS RBC membranes (28). This suggested that when unstable sickle cell RBC membranes bleb off vesicles, these vesicles are enriched in cholesterol and sphingolipid rich lipid rafts. Finally various post-translationally modified forms of spectrin membrane skeleton components changed by 2.5 fold in sickle cell RBC membranes (28). Two known proteolytic fragments of ankyrin (29–32) were present in greater quantity in SS RBC membranes; six PTM forms of proteins 4.1 were increased while one was decreased; and one protein spot each from protein 4.9 and tropomyosin 3 were decreased (Table 2). The value of 2D DIGE is that it allows us to detect multiple post translationally modified forms of the same protein, while the limitation of using two dimensional gels to separate and quantitate proteins has already been discussed above. We followed this initial study on sickle cell RBC membranes, with the use of cleavable isotope coded affinity tag (cICAT) technology coupled to tandem mass spectrometry to study the sickle cell versus control RBC membrane skeletal components (33). In this study, we found that the cICAT technology and changes in control populations led to only 20% variance in membrane skeleton protein ratios. We also found that these ratios from SS versus AA samples were not significantly different from 1 for spectrin subunit, spectrin β subunit, β-actin, and protein 4.1 (33). Therefore, while various PTM forms of proteins 4.1 change in SS versus AA RBC membranes as measured by 2D DIGE (28), the total content of protein 4.1 does not vary in the SS versus AA membrane skeleton as measured by cICAT technology (33). This is an example of why these two technologies are complementary and it is useful to utilize both. cICAT protein profiling is able to measure ratios of total protein 4.1 in SS versus AA samples with great precision (~20% variation in the technique); while 2D DIGE is able to determine ratios of specific post-translationally modified forms of protein 4.1 in SS versus AA samples, but with lower precision (2.5 fold changes). As the cICAT technique labels cysteine containing peptides only (34), it will miss many post-translational changes (33) that will not be missed by 2D DIGE (28). More recent use of iTRAQ (isobaric technique for relative and absolute quantitation) reagents overcome this cICAT related problem; as it labels terminal amines and –amino groups and therefore labels all tryptic peptides (35). It also allows comparisons of up to four distinct samples and overcomes the possibility of cysteine oxidation affecting ICAT results (34, 35). Because of the separate strengths of 2D DIGE, cICAT and iTRAQ technologies, we now apply all three in protein profiling studies.

Recently Prabakaran et al (36) have performed 2D DIGE analyses on RBC proteins derived from 20 schizophrenic subjects versus 20 controls. As they were studying whole RBC protein content, they utilized IEF fractionation to limit the hemoglobin content by discarding the protein fraction in the isoelectric point (pI) range of 6.2 – 10.0. This, of course, causes the loss of many other proteins that fell into this broad range of pI. The elimination of hemoglobin is an important and difficult problem in RBC proteomics. The use of hemoglobin antibodies is prohibitively costly, and not successful, because of the very high intracellular hemoglobin content in the RBC. We have found that gel filtration chromatography is an acceptable compromise between diminishing the hemoglobin content while limiting the loss of other proteins (16). Despite discarding this broad pI range hemoglobin containing fraction, Prabakaran et al observed ~ 1200 fluorescent RBC protein spots, 49 of which were significantly changed in the samples from schizophrenia patients (p 0.05). After in–gel trypsin digestion and tandem mass spectrometry, 8 unique proteins were found to demonstrate significant change. Two proteins were increased (selenium binding protein and glutathione reductase), while the other six decreased in schizophrenic patients (thioredoxin peroxidase, heat shock 70 kD protein, serum albumin, apolipoprotein A1, erythroid spectrin and β-actin). The changes in erythroid spectrin and β-actin probably reflect post-translational changes, and not total content, as described above. Selenium binding protein 1 (SBP1), glutathione reductase and thioredoxin are known to quench reactive oxygen species (ROS), oxidative stress is occurring in brain and RBCs in schizophrenia (36), and SBP1 has previously been suggested as a potential biomarker for schizophrenia. This proteomic study (36) allows the possibility of utilizing RBC proteomics for schizophrenia disease detection.

Although a description of malaria is beyond the scope of this review, we will mention one proteomic study that may supply new targets for antimalarial drugs and vaccines. Flovens et al biotinylated the surface proteins of Plasmodium parasite infected erythrocytes (37). They then used streptavidin affinity chromatography on solubilized infected RBC membranes to isolate parasite encoded proteins on the surface of the infected erythrocyte (PIESPs). Trypsin digestion, MuDPiT separation of peptides, tandem mass spectrometry, and bioinformatic analysis led to identification of 36 candidate PIESPs. The authors characterized two: PIESP1 (154 kD) and PIESP2 (49 kD) and demonstrated both to be associated with knob – like protrusions on the surface of parasite infected RBCs (37). These two proteins, both encoded by single copy genes, may prove to be excellent future therapeutic targets for malaria.

	The Altered Interactome in Sickle Cell RBCs

TOP Abstract Introduction A Status Report of... The Human RBC Interactome RBC Proteomics as it... The Altered Interactome in... Final Thoughts References

 
The powerful combination of proteomic and in silico techniques, described in this minireview, gives researchers the ability to identify protein content and PTM changes related to a specific disease, or disease severity, or drug and gene therapy treatment. These linked approaches represent the future of clinical identification of specific disease, its current stage or severity, and the effects and side effects of various treatments. We are utilizing protein profiling and interactome maps for all of these purposes in Sickle Cell Disease.

To visualize the impact of SCD on the erythrocyte interactome PPI network, proteins that were significantly altered in SCD patients are marked on the network graphs shown in Figures 2a and 2b. Figure 2a is the same as Figure 1a with SCD-altered protein gene symbols that are colored red, green, or blue. Red symbols represent proteins that increased at least 2.5-fold among SCD subjects compared to non-SCD subjects, green symbols represent proteins that decreased at least 2.5-fold among SCD subjects compared to non-SCD subjects, and blue symbols represent proteins with some isoforms or PTM forms that showed a decrease of at least 2.5-fold, and with other isoforms or PTM forms that showed an increase of at least 2.5-fold. Figure 2b is the ROD Box proteins with SCD-altered protein symbols colored as in Figure 2a.

Figure 2a illustrates how the altered proteins interact with other proteins in the complete network. Some of the former have a large number of connections with other proteins in the network (such as proteasomal subunits PSMA1, PSMB1, PSMC6 and chaperonins CCT 2, 4, 6A, 7), whereas some others are relatively isolated with very few links to the rest of the network (ex. catalase CAT). It can be seen from Figure 2b that 9 of the SCD altered proteins are closely connected to the subset of proteasome, chaperonin, and heat shock proteins (including catalase). That is, these 9 altered proteins are interacting partners with at least one protein in that subset. Therefore, many of the changes in the RBC membrane in SCD are found in the ROD Box.

Figure 3 shows that, with respect to their interactions with each other, SCD-altered proteins form two distinct groups: one small, connected group and the other containing pair-wise disconnected proteins. The connected component of this SCD interaction graph has an interesting structure from a graph theoretic standpoint as it is composed by three disjoint cliques of sizes four, three, and one, with the three-clique connecting the one-clique with the four-clique, where a clique is a complete subgraph (a subset of vertices of the graph that are all connected to each other).

Thus, the connected component is a linear sequence of cliques. We also observe from Figure 2 that certain SCD-altered proteins, such as ankyrin 1 (ANK1), dematin erythrocyte membrane protein band 4.9 (EPB49), heat shock protein 8 (HSPA8), proteasome subunit alpha type 1 (PSMA1) and proteasome subunit beta type 1 (PSMB1), are articulation points of the entire PPI network. If we remove such a point, then a previously connected component of the network gets partitioned into two or more disjointed subgraphs. Similarly, it can be seen in Figure 3 that chaperonin containing TCP1, subunit 6A isoform a (CCT6A), proteasome subunit alpha type 1 (PSMA1) and proteasome 26S subunit, and ATPase 6 (PSMC6) are the articulation points of the SCD network. For example, removing CCT6A from this network would separate the interconnected chaperonin proteins from the interconnected proteasomal proteins.

	Final Thoughts

TOP Abstract Introduction A Status Report of... The Human RBC Interactome RBC Proteomics as it... The Altered Interactome in... Final Thoughts References

 
The combination of proteomic and in silico approaches allows one to not only identify disease and/or drug related changes in the proteome, but to predict the changes in the protein interactome network that will cause disease related change of function. As an example, we are currently utilizing this unified approach to determine how proteomic changes in the protein profile of RBCs, WBCs and plasma are linked to SCD severity. We are also utilizing this approach to determine hydroxy urea dependent changes in the SCD RBC membrane protein profile (38). The result of this study has already demonstrated increases in catalase, chaperonin containing TCP1, aldehyde dehydrogenase and p55. Catalase (CAT) and chaperonin containing TCP1 (CCT6A) are in the ROD box. Aldehyde dehydrogenase and p55 are not in the ROD box and the confidence scores for their interactions were not sufficiently high.

The great sensitivity of the modern mass spectrometers indicates that contamination of an RBC preparation by even low levels of reticulocytes or WBCs can be problematic. All previous studies on the RBC proteome have made an attempt to limit this contamination. Reticulocytes can represent 0.1 to 1.0 percent of control RBC preparations, but increases greatly in the case of hematologic disorders such as SCD. We therefore have recently established a rapid, high volume and throughput Percoll density approach which allows the reduction of reticulocytes within control and SCD RBC preparations to less than 3 ppm (39). As all other technologies such as FACS, MACS, and long incubations at 4°C are far less efficacious, our new technology should become the standard within the RBC proteome field (39).

The combination of starting with highly purified reticulocyte free RBC preparations, constantly improving mass spectrometers and data bases, and the use of interactome in silico approaches have the field of RBC proteomics and disease ready to explode over the next few years. We hope that this review will help illuminate the path and approach for investigators within the field.

View this table: [in this window] [in a new window]   Table 1. Erythrocyte Proteins That Have Been Identified By Proteomic Methods

 

View this table: [in this window] [in a new window]   Table 2. The altered proteins in SS RBC membranes placed in functional categories

 

View larger version (59K): [in this window] [in a new window]   Figure 1a. Preliminary RBC Interactome Network Nodes give gene symbols of erythrocyte proteins and lines show interactions between proteins. The ROD box shows the region of the network that contains chaperonin, heat shock, and proteasome proteins along with their interacting partners and is expanded in 1b.

 

View larger version (43K): [in this window] [in a new window]   Figure 2a. Preliminary SCD RBC Interactome Network Same as Figures 1a and 1b with SCD-altered protein symbols colored red: SCD-altered proteins that increased > 2.5-fold; green: SCD-altered proteins that decreased > 2.5-fold; and blue: SCD-altered proteins that had some modified forms that increased > 2.5-fold and others that decreased > 2.5-fold.

 

View larger version (6K): [in this window] [in a new window]   Figure 3. PPI network of SCD-altered proteins Lines represent interactions among SCD-altered proteins only.

 

	Footnotes

 
Work described in this minireview was supported by a Sickle Cell Center grant from the National Institutes of Health HL070588, Project 11, awarded to Steven R. Goodman.

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TOP Abstract Introduction A Status Report of... The Human RBC Interactome RBC Proteomics as it... The Altered Interactome in... Final Thoughts References

 

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