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SARS Coronavirus is an enveloped virus containing three outer structural proteins, namely the membrane (M), envelope (E), and spike (S) proteins. Spike (S)-glycoprotein of the virus interacts with a cellular receptor and mediates membrane fusion to allow viral entry into susceptible target cells. Accordingly, S-protein plays an important role in virus infection cycle and is the primary target of neutralizing antibodies.It has recently been shown that SARS is caused by a human coronavirus. Human coronaviruses are the major cause of upper respiratory tract illness in humans, such as the common cold. Coronaviruses are positive-stranded RNA viruses, featuring the largest viral RNA genomes known to date (27-31 kb). The first step in coronavirus infection is binding of the viral spike protein, a 139-kDa protein, to certain receptors on host cells. The spike protein is the main surface antigen of the coronavirus. The most prominent protein in the culture supernatants infected with SARS virus is a 46 kDa nucleocapsid protein. This suggests that the nucleocapsid protein is a major immunogen that may be useful for early diagnostics.

Pro-opiomelanocortin preproprotein (POMC) is a polypeptide hormone precursor which experiences extensive, tissue-specific, post-translational processing via cleavage by subtilisin-like enzymes known as prohormone convertases. POMC regulates the corticosteroid production in the adrenal cortex. Furthermore, POMC is cleaved into ten hormone chains named NPP, g-MSH, ACTH, a-MSH, CLIP, Lipotropin b, Lipotropin g, b-MSH,b endorphin and Met-enkephalin. POMC gene defects are the cause of POMC deficiency, which is characterized by red hair and adrenal insufficiency.

The La protein is a 47 kDa polypeptide that frequently acts as an autoantigen in systemic lupus erythematosus and Sjogren's syndrome patients. La is involved in various aspects of RNA metabolism, including binding and protecting 3-prime UUU(OH) elements of newly RNA polymerase III - transcribed RNA, processing 5-prime and 3-prime ends of pre-tRNA precursors, acting as an RNA chaperone, and binding viral RNAs linked to hepatitis C virus. It occurs in both the nucleus and the cytoplasm, where it assumes different roles. In the nucleus, La protein facilitates the production of tRNAs, acting as an RNA polymerase III (RNAP III) transcription factor by attaching to the U-rich 3'UTR of nascent transcripts, aiding in their folding and maturation. In the cytoplasm, La protein facilitates the translation of specific mRNAs, acting as a translation factor. As an RNA binding protein (RBP), La protein associates with subsets of mRNAs which contain a 5'-terminal oligopyrimidine (5'TOP) motif known to direct protein synthesis. The binding of La protein to particular classes of RNA molecules regulates their downstream processing, guards them from endonuclease digestion, and organizes their export from the nucleus. La/SS-B appears to be readily disposed to proteolysis, which results in many smaller (42kD, 320, and 270) nevertheless still immunoreactive polypeptides. La/SS-B antigen is strongly conserved across species. Anti-La/SS-B autoantibodies were originally found as precipitating autoantibodies in sera of Sjogren's Syndrome patients and referred to as SjT. Anti-La/SS-B precipitins are most frequently found in Sjogren's Syndrome, Systemic Lupus Erythematosus (SLE) and Subacute Cutaneous Lupus. Also, there seems to be a correlation between anti-La/SS-B and the absence of nephritis in SLE patients.

WHSC2 (NELF-A) is a protein factor required for DRB-sensitive transcription. WHSC2 is one of the 5 components of the multisubunit NELF complex which cooperates with DSIF to repress RNA polymerase II elongation. The Wolf-Hirschhorn syndrome is a multiple malformation syndrome characterized by mental and developmental defects resulting from a hemizygous deletion of the distal short arm of chromosome 4 (4p16.3).

Streptokinase is an extracellular metallo-enzymeproduced by beta-haemolytic streptococcusand is used as an effective and cheap clot-dissolving medicationin some cases of myocardial infarction(heart attack) and pulmonary embolism.
It belongs to a group of medications known as fibrinolytics, and works by activating plasminogenthrough cleavage to produce plasmin.

Antigen 85A is a member of the antigen 85 complex (Antigen 85A, B, C). The enzymes of the antigen 85 complex have mycolyltransferase activity and catalyze the synthesis of the very rich glycolipid of the mycobacterial cell wall, the cord factor (trehalose 6,6'-dimycolate, TDM). The cord factor is vital for the integrity of the mycobacterial cell wall and pathogenesis of the bacillus. TDM is synthesized from two molecules of trehalose-6'-monomycolate (TMM) by Antigen 85A.

Ectodysplasin A Receptor, also known as EDAR belongs to the tumor necrosis factor receptor family. EDAR is a receptor for the soluble ligand ectodysplasin A, and is capable of activating the nuclear factor-kappaB, JNK, as well as caspase-independent cell death pathways. EDAR is necessary for the development of hair, teeth, and other ectodermal derivatives. Furthermore, mutations in EDAR resulted in autosomal dominant and recessive forms of hypohidrotic ectodermal dysplasia.

Clusterin also known as Apolipoprotein J (APO-J) is a 75-80 kD disulfide-linked heterodimeric protein containing about 30% of N-linked carbohydrate rich in sialic acid but truncated forms targeted to the nucleus have also been identified.
The precursor polypeptide chain is cleaved proteolytically to remove the 22-mer secretory signal peptide and subsequently between residues 227/228 to generate the a and b chains. These are assembled in anti-parallel to give a heterodimeric molecule in which the cysteine-rich centers are linked by 5 disulfide bridges and are flanked by 2 predicted coiled-coil a-helices and 3 predicted amphipathic a-helices.
Across a broad range of species clusterin shows a high degree of sequence homology ranging from 70% -80%. It is nearly ubiquitously expressed in most mammalian tissues and can be found in plasma, milk, urine, cerebrospinal fluid and semen.
It is able to bind and form complexes with numerous partners such as immunoglobulins, lipids, heparin, bacteria, complement components, paraoxonase, beta amyloid, leptin and others. Clusterin has been ascribed a plethora of functions such as phagocyte recruitment, aggregation induction, complement attack prevention, apoptosis inhibition, membrane remodeling, lipid transport, hormone transport and/or scavenging, matrix metalloproteinase inhibition.
Clusterin is up/down regulated on the mRNA or protein level in many pathological and clinically relevant situations including cancer, organ regeneration, infection, Alzheimer disease, retinitis pigmentosa, myocardial infarction, renal tubular damage, autoimmunity and others.

RPA-interacting protein isoform d (RPAIN) is a single-stranded-DNA binding protein which participates in various eukaryotic DNA processes such as replication, repair and recombination. RPAIN interacting protein has been indicated as an adapter protein that is involved in RPA nuclear import instead of the prototypical importin proteins that normally mediate nuclear import. RPAIN is mainly expressed in pancreas, kidney, muscle, liver, lung, placenta, brain, heart, leukocytes, colon, intestine, ovary, testis, prostate, thymus and spleen.

Vesicle-trafficking protein SEC22b precursor (SEC22B) is a member of the synaptobrevin family. SEC22B forms a complex with SNARE and it is believed to have a role in the ER-Golgi protein trafficking. SEC22B has a strong similarity to the mouse and Chinese hamster proteins.

SEMG1 is the predominant protein in semen. The secreted protein takes part in the formation of a gel matrix which encases ejaculated spermatozoa. The prostate-specific antigen (PSA) protease processes SEMG1 into smaller peptides, with each possibly having a separate function. The proteolysis process breaks down the gel matrix and allows the spermatozoa to shift more freely. 2 transcript variants encoding different isoforms have been found for SEMG1.

Nucleic acid binding protein 1 is a part of the SOSS complex, amultiprotein complex which functions downstream of the MRN complex to promote DNA repair and G2/M checkpoint.In the SOSS complex, NABP1 acts as a sensor of single-stranded DNA which binds to single-stranded DNA, inparticular to polypyrimidines. The SOSS complex links with DNA lesions and affects diverse endpoints in the cellular DNA damage response including cell-cycle checkpoint activation, recombinational repair andmaintenance of genomic stability. NABP1 is essential for efficient homologous recombination-dependent repairof double-strand breaks (DSBs) and ATM-dependent signaling pathways.

Processing of Precursor 4 (POP4) is a member of the eukaryotic/archaeal RNase P protein component 1 family. POP4 is one of the protein subunits of the small nucleolar ribonucleoprotein complexes: the endoribonuclease for mitochondrial RNA processing complex and the ribonuclease P complex. POP4 is confined to the nucleus and associates promptly with the RNA component of this complexes.POP4 is participating in processing of precursor RNAs.

Maltose Binding Protein is a member of the maltose/maltodextrin system of E.Coli, which is accountable for the uptake and efficient catabolism of maltodextrins. The maltose/maltodextrin is a complex regulatory and transport system involving many proteins and protein complexes.
MBP elevates the yield of its fusion partner in many cases and is often able to promote the solubility of polypeptides to which it is fused.

Macrophage Inflammatory Proteins (MIP) belong to the family of chemotactic cytokines known as chemokines. In humans, there are two major forms, MIP-1a and MIP-1b that are now officially named CCL3 and CCL4 respectively. Both are major factors produced by macrophages after they are stimulated with bacterial endotoxins. They activate human granulocytes (neutrophils, eosinophils and basophils) which can lead to acute neutrophilic inflammation. They also induce the synthesis and release of other pro-inflammatory cytokines such as interleukin 1 (IL-1), IL-6 and TNF-a from fibroblasts and macrophages. The genes for CCL3 and CCL4 are both located on human chromosome 17.

Macrophage Inflammatory Proteins (MIP) belong to the family of chemotactic cytokines known as chemokines. In humans, there are two major forms, MIP-1a and MIP-1b that are now officially named CCL3 and CCL4 respectively. Both are major factors produced by macrophages after they are stimulated with bacterial endotoxins. They activate human granulocytes (neutrophils, eosinophils and basophils) which can lead to acute neutrophilic inflammation. They also induce the synthesis and release of other pro-inflammatory cytokines such as interleukin 1 (IL-1), IL-6 and TNF-a from fibroblasts and macrophages. The genes for CCL3 and CCL4 are both located on human chromosome 17.

HPSE also known as Heparanase-1 is an enzyme which cleaves heparan sulfate proteoglycans to allow cell movement through changing the extracellular matrix. In fact, the Heparan sulfate proteoglycans are major components of the basement membrane and extracellular matrix. In addition, this cleavage can release bioactive molecules from the extracellular matrix. HPSE is significant for the overall degradation of proteins in lysosomes.

Chemokine (C-X-C motif) ligand (CXCL7) is a small cytokine belonging to the CXC chemokine family. It is a protein that is released in large amounts from platelets following their activation. It stimulates various processes including mitogenesis, synthesis of extracellular matrix, glucose metabolism and synthesis of plasminogen activator.

Sarcoglycan Beta, also known as SGCB, is a part of the sarcoglycan family. SGCB belongs to the sarcoglycan complex which is a subcomplex of the dystrophin-glycoprotein complex that connects between the F-actin cytoskeleton and the extracellular matrix.

EFNA3 belongs to the ephrin (EPH) family. The ephrins and EPH-related receptors include thelargest subfamily of receptor protein-tyrosine kinases which have been implicated in mediating developmental events, especially in the nervous system and in erythropoiesis. Ephrins are divided into the ephrin-A (EFNA) class and the ephrin-B (EFNB) class, based on their structures and sequence relationships. The Ephrins from the EFNA class are anchored to the membrane by aglycosylphosphatidylinositol linkage, while the others from the EFNB class are transmembrane proteins.

Serine/arginine-rich splicing factor 1 (SFRS1) belongs to the arginine/serine-rich splicing factor protein family, and functions in both constitutive and alternative pre-mRNA splicing. SFRS1 binds to pre-mRNA transcripts and components of the spliceosome, and can either initiate or inhibit splicing depending on the position of the pre-mRNA binding site. The ability of SFRS1 to activate splicing is controlled by phosphorylation and interactions with other splicing factor associated proteins.

O-Sialoglycoprotein Endopeptidase, also known as OSGEP is a member of the KAE1 / TsaD family. OSGEP is essential for the formation of threonylcarbamoyl group on adenosine at position 37 (t6A37) in tRNAs which read codons beginning with adenine. OSGEP take a direct catalytic part in the above reaction, however other proteins of the complex are required to fulfill this activity.

Calbindins are Ca-binding proteins belonging to the troponin C superfamily. CALB28K/Calbindin1/CALB1 (D28K/Spot35 protein or cholecalcin, rat 261 aa; mouse 261 aa; human 261-aa, chromosome 8q21.3-q22.1) was originally described as 27-kDA induced by vitamin D in the duodenum of chicken. In mammals, it is expressed in the kidney, pancreatic islets, and brain. In brain, its synthesis is independent of vitamin D. CABP28K contains 4 active and 2 inactive EF-hand Ca-binding domains. The gene for CABP28K is clustered in the same region as carbonic anhydrase. The neurons in the brains of patients with Huntington disease are CAB28K depleted. There are two types of CaBPs: the "trigger"- and the "buffer"-CaBPs. The conformation of "trigger" type CaBPs changes upon Ca2+ binding and exposes regions on protein that interact with target molecules, thus altering their activity. The buffer-type CABP are thought to control the intracellular calcium concentration. Calbindin D-28K is found predominantly in subpopulations of central and peripheral nervous system neurons, and in certain epithelial cells involved in Ca2+ transport such as distal tubular cells and cortical collecting tubules of the kidney, and in enteric neuroendocrine cells.

Geminin is a 25 kDa nuclear protein, which inhibits DNA replication and is degraded during the mitotic phase of the cell cycle. Geminin controls replication by binding to the licensing factor Cdt1, and is involved in neural differentiation. In addition, Geminin directly interacts with Six3 and Hox homeodomain proteins during embryogenesis and inhibits their functions. Geminin can also promote DNA replication. Geminin has 2 roles in 2 different stages of the cell cycle: Geminin is a negative regulator of DNA replication during the “S phase” of the cell cycle. Inhibition of Geminin during the “S phase” (by RNAi) results in an additional round of replication of portions of the genome. During the “M phase” of the cell cycle (mitosis) Geminin stabilizes the replication factor Cdt1 promoting DNA replication during the next cell cycle. Moreover, inhibition of Geminin during mitosis (by RNAi) causes destabilization of Cdt1 protein and impairment of DNA replication during the next cell cycle. Geminin thus guarantees that only one round of replication occurs during each cell cycle. It was discovered that Geminin is overexpressed in a number of malignancies and cancer cell lines. This maintains the concept that Geminin has also a positive role in DNA replication and cell cycle progression. Geminin accumulates through S, G2 and M phases of the cell cycle but is absent during the G1 phase. During the metaphase/anaphase transition of mitosis Geminin levels decrease.