Small Glutamine-Rich Tetratricopeptide Repeat-Containing Protein α (SGTA) is an ubiquitously expressed protein which belongs to the SGT Family. SGTA contains three TPR Protein-Protein Interaction Duplicates. SGTA is a co-chaperone that binds directly to HSC70 and HSP70 and regulates their ATPase activity. SGTA is capable of interacting with the major nonstructural protein of Parvovirus H-1 and 70-kDa heat shock cognate protein. It interacts with NS1 from Parvovirus H-1, with Vpu and Gag from HIV-1. It also interacts with SARS-CoV Accessory Protein 7a, DNAJC5 and DNAJC5B. However, its function is not known. Since this transcript is expressed ubiquitously in various tissues, SGTA may serve a housekeeping function.
SH2 Domain-Containing Protein 1A,(SH2D1A) contains one SH2 domain and a short tail and is localized in the cytoplasm. SH2D1A is expressed at a high level in the thymus and the lung, with lower expression levels in the spleen and the liver. SH2D1A acts as an inhibitor of the signaling lymphocyte activation molecule (SLAM) self-association. In addition, SH2D1A mediates interaction between FYN and SLAMF1. It is also thought to regulate the activity of the neurotrophin receptors NTRK1, NTRK2 and NTRK3.
SH2 domain-containing protein 1A (SH2D1A / SAP) is a 128 amino acid protein, containing a single Src homology 2 (SH2) domain, flanked by 5 amino acids at the N-terminus and 25 amino acids at the C-terminus. The absence of a catalytic domain and the presence of an SH2 domain suggest that SH2D1A regulates one or more signal transduction pathways. SH2D1A interacts with signaling lymphocytic activation molecule (SLAM), which is a transmembrane protein expressed on the surface of activated T and B cells. SH2D1A (SAP) interacts via its SH2 domain with a motif (TIYXXV) present in the cytoplasmic tail of the cell-surface receptors, including CD150 / SLAM, CD84, CD229 / Ly-9, and CD244 / 2B4. SH2D1A was expressed in EBV-carrying, tumor phenotype representative (type I), but not in EBV-carrying lymphoblastoid cell line (LCL)-like (type III) or EBV-negative Burkitt lymphoma (BL) lines. It has been supposed to be related to the X-linked lymphoproliferative disease which is also known as Duncan's disease or Purtilo syndrome.
SHISA3 encodes a single-transmembrane protein which is one of nine members of a family of transmembrane adaptors that modulate both WNT and FGF signaling by blocking the maturation and transport of their receptors to the cell surface. Members of this family contain an N-terminal cysteine-rich domain with a distinct cysteine pattern, a single transmembrane domain, and a C-terminal proline-rich, low complexity region. The encoded protein acts as a tumor suppressor by accelerating beta-catenin degradation.
Serine Hydroxymethyltransferase Cytosolic (SHMT1) is a member of the SHMT family. SHMT1 is a cytoplasmic protein and exists as a homotetramer. SHMT1 catalyzes the reversible conversion of serine and tetrahydrofolate to glycine and 5,10-methylene tetrahydrofolate. This reaction provides one carbon unit for the synthesis of methionine, thymidylate, and purines in the cytoplasm. A reduction in SHMT1 levels would result in less glycine that could affect the nervous system by acting as an agonist to the NMDA receptor and this could be a mechanism behind Smith-Magenis syndrome.
Sialate O-acetylesterase belongs to the family of hydrolases, specifically those acting on carboxylic ester bonds. It is widely expressed with high expression in the testis, prostate, and colon. The systematic name of this enzyme class is N-acyl-O-acetylneuraminate O-acetylhydrolase. Other names in common use include N-acetylneuraminate acetyltransferase, sialate 9(4)-O-acetylesterase, and sialidase. Sialate O-acetylesterase catalyzes the removal of O-acetyl ester groups from position 9 of the parent sialic acid, N-acetylneuraminic acid. Defects in Sialate O-acetylesterase are a cause of autoimmune disease type 6 (AIS6). Individuals manifesting susceptibility to autoimmune disease type 6 can suffer from juvenile idiopathic arthritis, rheumatoid arthritis, multiple sclerosis, Sjogren syndrome, systemic lupus erythematosus, type 1 diabetes, ulcerative colitis, and Crohn disease.
Sialate O-Acetylesterase (SIAE) belongs to the family of hydrolases, specifically those acting on carboxylic ester bonds. SIAE is widely expressed with high expression levels in the testis, prostate, and colon. SIAE catalyzes N-acetyl-O-acetylneuraminate and H2O to N-acetylneuraminate and acetate. SIAE removes O-acetyl ester groups from position 9 of the parent sialic acid, N-acetylneuraminic acid. SIAE down-regulates B lymphocyte antigen receptor signaling (involving CD22), and is required for immunological tolerance. Loss of function mutations in SIAE are much more frequently found in humans with autoimmune diseases especially rheumatoid arthritis and type 1 diabetes.
Human Siglec-15 is a transmembrane glycoprotein in the Siglec family. Siglecs are type I transmembrane proteins where the NH3+-terminus is in the extracellular space and the COO--terminus is cytosolic. Each Siglec contains an N-terminal V-type immunoglobulin domain (Ig domain) which acts as the binding receptor for sialic acid. These lectins are placed into the group of I-type lectins because the lectin domain is an immunoglobulin fold. All Siglecs are extended from the cell surface by C2-type Ig domains which have no binding activity. Siglecs differ in the number of these C2-type domains. Human Siglec-15 consists of a 244 amino acid (aa) extracellular domain (ECD) with two Ig-like domains, a 21 aa transmembrane segment, and a 44 aa cytoplasmic domain. Siglec-15 function is important for osteoclast formation and TRANCE/RANK Ligand signaling in osteoclasts.
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