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Streptavidin is a tetrameric protein secreted by Streptomyces avidinii which binds firmly to biotin. Streptavidin is wilyde used in molecular biology through its unique high affinity for the vitamin biotin. The dissociation constant (Kd) of the biotin-streptavidin complex is about ~10-15 mol/L. The strong affinity recognition of biotin and biotinylated molecules has made streptavidin one of the most important components in diagnostics and laboratory kits. The streptavidin/biotin system has one of the biggest free energies of association of yet observed for noncovalent binding of a protein and small ligand in aqueous solution (K_assoc = 10**14). The complexes are also extremely stable over a wide range of temperature and pH.

PGK1 is an X-linked enzyme that has a major role in the glycolytic pathway. PGK1 is a glycolytic enzyme which catalyzes the conversion of 1,3-diphosphoglycerate to 3-phosphoglycerate, generating an ATP molecule. PGK1 may also act as a cofactor for polymerase alpha. Defects in the PGK1 gene are usually associated with chronic hemolytic anemia, though it can be accompanied by either mental retardation or muscular disease (rhabdomyolysis). Overexpression of PGK1 and its signalling targets are possibly an expression-pathway in diffuse primary gastric carcinomas promoting peritoneal dissemination. It was shown that PGK1 is differentially expressed in the dorsolateral prefrontal cortex from patients with schizophrenia.

Vps20-associated 1 homolog (VTA1) is a member of the VTA1 family. The VTA1 protein is involved in the endosomal multivesicular bodies (MVB) pathway. Furthermore, VTA1 is interacts with CHMP1B, CHMP2A, CHMP5, VPS4B, KIAA0174 (IST1) and possibly CHMP3. VTA1 is believed to be a cofactor of VPS4A/B, which catalyzes membrane-associated ESCRT-III assemblies. In addition, VTA1 is involved in the sorting and down-regulation of EGFR and also in HIV-1 budding.

Thymidylate synthase catalyzes the methylation of deoxyuridylate to deoxythymidylate using 5,10-methylenetetrahydrofolate as a cofactor which maintains the dTMP (thymidine-5-prime monophosphate) pool vital for DNA replication and repair. Thymidylate synthase plays an important role as a cancer chemotherapeutic agent. Thymidylate synthase is the primary site of action for 5-fluorouracil, 5-fluoro-2-prime-deoxyuridine, and several folate analogs.

Glutamyl-TRNA Amidotransferase, Subunit C also known as GATC allows the formation of properly charged Gln-tRNA(Gln) through the transamidation of misacylated Glu-tRNA(Gln) in the mitochondria. The reaction occurs in the attendance of glutamine and ATP through an activated gamma-phospho-Glu-tRNA(Gln). In addition, GATC is subunit of the heterotrimeric GatCAB amidotransferase (AdT) complex, composed of A (QRSL1), B (PET112) and C (GATC) subunits.

Plasminogen activator inhibitor-1 is the principal inhibitor of tissue plasminogen activator(tPA) and urokinase(uPA), the activators of plasminogenand hence fibrinolysis(the physiological breakdown of blood clots). It is a serine protease inhibitor(serpin) protein (SERPINE1). The other PAI, plasminogen activator inhibitor-2(PAI-2) is secreted by the placentaand only present in significant amounts during pregnancy. In addition, protease nexinacts as an inhibitor of tPA and urokinase. PAI-1, however, is the main inhibitor of the plasminogen activators.

E.Coli Uracil DNA Glycosilase (UNG) catalyses the release of free Uracil from Uracil-containing DNA. UNG efficiently hydrolyzes uracil from signle-stranded or double-stranded DNA, but not from oligomers (6 fewer bases).

FIS1 is part of the mitochondrial complex that promotes mitochondrial fission. FIS1 induces cytochrome C discharge from the mitochondrion to the cytosol, eventually leading to apoptosis. FIS1 participates in peroxisomal growth and division. The C terminus is required for mitochondrial localisation, while the N teminus is necessary for mitochondrial fission.

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.

CD20 is a member of the membrane-spanning 4A gene family. Members of this nascent protein family are characterized by common structural features and similar intron/exon splice boundaries and display unique expression patterns among hematopoietic cells and nonlymphoid tissues. CD20 plays a role in the development and differentiation of B-cells into plasma cells. CD20 is localized to 11q12, among a cluster of family members. Alternative splicing of this gene results in two transcript variants which encode the same protein.

Cytokeratin 23 (KRT23) is a 422 amino acid intermediate filament protein. The human KRT23 gene is found on chromosome 17q21.2. Type I cytokeratins consist of acidic proteins which are organized in pairs of heterotypic keratin chains. The cytokeratin proteins have an essential role in differentiation, plus tissue specialization and function, and epithelial cells structure maintenance. Cytokeratins are portrayed to be differentiation markers in a number of epithelial cancers.

RANKL binds to tnfrsf11b/opg and to tnfrsf11a/rank. Osteoclast differentiation and activation factor. Augments the ability of dendritic cells to stimulate naive t-cell proliferation. May be an important regulator of interactions between t-cells and dendritic cells and may play a role in the regulation of the t-cell-dependent immune response. sRANKL may also play an important role in enhanced bone-resorption in humoral hypercalcemia of malignancy. By injecting soluble RANKL, novel osteopenia model mice were established in only 50 hours. Degree of bone loss can be controlled by changing doses of sRANKL. RANKL can be used in establishing osteopenia model for in vivo screening of drugs for osteoporosis, determination of effect and mechanism, evaluation of bone anabolic drugs.

B220 (CD45R) is a member of the protein tyrosine phosphatase (PTP) family. PTPs are known to be signaling molecules that regulate a variety of cellular processes including cell growth, differentiation, mitotic cycle, and oncogenic transformation. This PTP contains an extracellular domain, a single transmembrane segment and two tandem intracytoplasmic catalytic domains, and thus belongs to receptor type PTP. This gene is specifically expressed in hematopoietic cells. This PTP has been shown to be an essential regulator of T- and B-cell antigen receptor signaling. It functions through either direct interaction with components of the antigen receptor complexes, or by activating various Src family kinases required for the antigen receptor signaling. This PTP also suppresses JAK kinases, and thus functions as a regulator of cytokine receptor signaling. Four alternatively spliced transcripts variants of this gene, which encode distinct isoforms, have been reported.
B220 (CD45R) is required for t-cell activation through the antigen receptor. The first ptpase domain has enzymatic activity, while the second one seems to affect the substrate specificity of the first one.

A natural cytotoxicity receptor (NCR) NKp46 has been shown to represent a novel NK cell-specific molecule involved in human NK cell activation. The natural cytotoxicity receptors (NCRs) are a recently characterized family of Ig-like activation receptors that appear to be major triggering receptors in tumor cell recognition. The three known NCRs include NKp46 and NKp30, which are expressed on circulating NKcells, and NKp44, which is expressed only on activating NK cells. NKp46 has been implicated in NK cell-mediated lysis of several autologous tumor cells, pathogen-infected cell lines and mononuclear phagocytes infected with an intracellular bacterium. The Lysis of tumor cells by NK-cells involves recognition by NKp46 of heparan sulfate moieties of membrane heparan sulfate proteoglycans. Furthermore, NKp46 is a surface receptor involved in NK-cell cell death by apoptosis. NKp46 has two extracellular Ig-like domains followed by a ~40 residue stalk region, a type I transmembrane domain, and a short cytoplasmic tail. The extracellular Ig-like domain of NKp46 (22-255aa) is purified by FPLC gel-filtration chromatography, after refolding of the isolated inclusion bodies in a redox buffer. In addition, engagement of the antigen with the monoclonal antibody stimulates intracellular calcium levels and the synthesis of cytokines. CD59 is an NKp46 coreceptor (by physical association) together they activate cytotoxicity of human NK-cells, their engagement results in tyrosine phosphorylation of CD3-zeta chains associated with NKp46. Reduced cell surface expression of NKp46 and other NK-cell receptors is linked to the impaired NK-cell cytolytic function in viremic HIV-1 infection.

Von Hippel-Lindau disease is a dominant inherited syndrome characterized by the predisposition to develop various kinds of benign and malignant tumors, including clear cell renal carcinomas, pheochromocytomas and hemangioblastomas of the central nervous system and retina. VHL syndrome is caused by germline mutation in the VHL tumor suppressor, and VHL tumors are associated with loss or mutation of the remaining wild-type allele. VHL has two domains: a roughly 100-residue NH2-terminal domain rich in b sheet (b-domain) and a smaller a-helical domain (a-domain), held together by two linkers and a polar interface. VHL protein is also involved in the degradation of hypoxia-inducible factor (HIF).

Hepatitis B is one of a few known non-retroviralviruses which employ reverse transcriptionas a part of its replication process. (HIV, a completely unrelated virus, also uses reverse transcription, but it is a retrovirus.) HBV invades the cell by binding to surface receptor and become internalized. The viral core particles then migrate to the hepatocyte nucleus and the partially double-stranded, relaxed circular genomes (RC-DNA) are repaired to form a covalently closed circular DNA (cccDNA), which is the template for viral genomic and sub-genomic RNAs by cellular RNA polymerase II. Of these, the pregenomic RNA (pgRNA is selectively packaged into progeny capsids and is then reverse-transcribed into new RC-DNA. The core can either bud into the endoplasmic reticulum to be enveloped or exported from the cell or recycled back into the genome for conversion to cccDNA.

Estrogen receptors α (ERα, ER; NR3A1) is a member of the steroid hormone receptor family. ERα is a ligand-activated transcription factor. ERα contain DNA binding and ligand binding domains. ERα is expressed in a wide variety of tissues, including ovary, uterus, breast, prostate, testis, epididymis, bones, bladder, kidney, heart, vessel wall, pituitary gland and hypothalamus. ER plays a variety of important roles in the maintenance of the reproductive, cardiovascular, musculoskeletal and central nervous systems. The natural ligand for ER is 17β-estradiol, the classical estrogenic compound. The binding of estrogen to ER induces a conformational change and triggers a cascade of events, including dissociation from heat shock proteins, receptor dimerization, phosphorylation and the association of the hormone activated receptor with specific regulatory elements in target genes.

Glucose-6-phosphate isomerase (GPI) is a part of the GPI family whose members encode multifunctional phosphoglucose isomerase proteins involved in energy pathways. GPI is a dimeric enzyme which catalyzes the reversible isomerization of glucose-6-phosphate and fructose-6-phosphate. Mammalian GPI also functions as a tumor-secreted cytokine and an angiogenic factor (AMF) which stimulates endothelial cell motility. In addition, GPI is a neurotrophic factor (Neuroleukin) for spinal and sensory neurons. GPI performs in different capacities inside and outside the cell. In the cytoplasm, GPI is involved in glycolysis and gluconeogenesis, while outside the cell it acts as a neurotrophic factor for spinal and sensory neurons.
Defects in the GPI gene cause the nonspherocytic hemolytic anemia and a severe enzyme deficiency can be linked to hydrops fetalis, immediate neonatal death and neurological impairment.

MGAT2 is an enzyme which takes part in the catalyzation of a crucial step in the reaction of oligomannose which converts to complex N-glycans. MGAT2 has three domains, classic to glycosyltransferase: short N-terminal cytoplasmic domain, a C-terminal catalytic domain and hydrophobic non-cleavable signal-anchor domain. The enzyme MGAT2 is encoded by the MGAT2 gene in humans. There are no introns in the DNA coding the gene, therefore mutations in the MGAT2 will result in carbohydrate-deficient glycoprotein syndrome, type II.

KRT20 is a member of the keratin family. The keratins are intermediate filament proteins responsible for the structural integrity of epithelial cells and are subdivided into cytokeratins and hair keratins. The type I cytokeratins consist of acidic proteins which are arranged in pairs of heterotypic keratin chains. This cytokeratin is a major cellular protein of mature enterocytes and goblet cells and is specifically expressed in the gastric and intestinal mucosa. The type I cytokeratin genes are clustered in a region of chromosome 17q12-q21.

NCS1 is part of the neuronal calcium sensor gene family, which encode calcium-binding proteins expressed primarily in neurons. NCS1 regulates G protein-coupled receptor phosphorylation in a calcium-dependent manner and can substitute for calmodulin. NCS1 is related with secretory granules and modulates synaptic transmission and synaptic plasticity. NCS1 regulates GRK1 and substitutes for calmodulin. NCS1 stimulates PI4KB kinase activity and participates in long-term synaptic plasticity through its interaction with PICK1. NCS1 takes part in neuron differentiation through inhibition of the activity of N-type voltage-gated calcium channel.