HSPA8, also known as HSC70, is a member of the heat shock protein family due to homology with other heat shock proteins. The heat shock protein 70 family is comprised by both heat-inducible and constitutively expressed members. The latter are called heat-shock cognate proteins. HSPA8 belongs to the heat-shock cognate subgroup. Members of the human heat-shock protein multigene family have several highly conserved proteins with structural and functional properties in common, but vary in the extent of their inducibility in response to metabolic stress. HSPA8 is constitutively expressed and performs functions related to normal cellular processes. This protein binds to nascent polypeptides to facilitate correct protein folding. It also functions as an ATPase in the disassembly of clathrin-coated vesicles during transport of membrane components through the cell. Two alternatively spliced variants have been characterized to date. HSPA8 acts as a repressor of transcriptional activation. It inhibits the transcriptional coactivator activity of CITED1 on Smad-mediated transcription. Isoform 2 may function as an endogenous inhibitory regulator of HSC70 by competing the co-chaperones. It also is a ATPase that works with auxilin to remove clathrin coated vesicles. In neurons, synaptojanin is also an important protein involved in vesicle uncoating.
Heat Shock Protein β-11 (HSPB11) is a stress-responsive protein that is required to deal with proteotoxic stresses. HSPB11 is composed of an IFT complex B composed of IFT88, IFT57, TRAF3IP1, IFT52, IFT27, HSPB11 and IFT20 and is detected in placenta. HSPB11 has beeb shown to form oligomeric complexes and prevent the aggregation of in vitro denaturated aldolase and glyceraldehyde-3-phosphate dehydrogenase in accordance with the chaperone model of HSPB1 and HSPB5. HSPB11 overexpression protected against etoposide-induced cell death that correlated with a decreased release of mitochondrial Cytochrome C into the cytosol. Inhibition of HSP90 function completely abrogated the protective effect of HSPB11. This data suggests that at least in the case of HSPB11, interaction with other chaperone machines besides HSPA1A may contribute to functional specificity and cellular functioning.
Heat shock protein beta-2(HSPB2) is a protein that in humans is encoded by the HSPB2 gene. HSPB2 belongs to the superfamily of small heat-shock proteins containing a conservative alpha-crystallin domain at the C-terminal part of the molecule. It is expressed preferentially in the heart and skeletal muscle. HSPB2 has been shown to interact with TRAF6, HSPB8, Myotonic dystrophy protein kinase and CRYAB. HSPB2 regulates Myotonic Dystrophy Protein Kinase, which plays an important role in maintenance of muscle structure and function.
PSG2 is a secreted protein that in humans is encoded by the PSG2 gene. It is a member of the human pregnancy-specific glycoproteins (PSGs) family. These proteins are synthesized in large amounts by placental trophoblasts and released into the maternal circulation during pregnancy. PSG2 consist of a single N domain, with structural similarity to the immunoglobulin variable domains, followed by a variable number of immunoglobulin constant-like A and/or B domains. It has an arg-gly-asp (RGD) motif, which has been shown to function as an adhesion recognition signal for several integrins, in the N-terminal domain.
Heat shock protein beta-8 (HSPB8) belongs to the small heat shock protein (HSP20) family. This protein can be inducted by 17-beta-estradiol, and is predominantly expressed in skeletal muscle and heat, mainly located in the cytoplasm and nucleus. HSPB8 usually exists in monomer, it can interact with HSPB1 and DNAJB6. HSPB8 displays temperature-dependent chaperone activity,appears to be involved in regulation of cell proliferation, apoptosis, and carcinogenesis, and mutations in this gene have been associated with different neuromuscular diseases, including Charcot-Marie-Tooth disease.
HSPD1, also known as HSP60, is a member of the chaperonin family. HSPD1 may function as a signaling molecule in the innate immune system. This protein is essential for the folding and assembly of newly imported proteins in the mitochondria. It may also prevent misfolding and promote the refolding and proper assembly of unfolded polypeptides generated under stress conditions in the mitochondrial matrix. HSPD1 gene is adjacent to a related family member and the region between the 2 genes functions as a bidirectional promoter. Several pseudogenes have been associated with this gene. Mutations associated with this gene cause autosomal recessive spastic paraplegia 13.Defects in HSPD1 are a cause of spastic paraplegia autosomal dominant type 13 (SPG13). Spastic paraplegia is a degenerative spinal cord disorder characterized by a slow, gradual, progressive weakness and spasticity of the lower limbs. Defects in HSPD1 are the cause of leukodystrophy hypomyelinating type 4 (HLD4); also called mitochondrial HSP60 chaperonopathy or MitCHAP-60 disease. HLD4 is a severe autosomal recessive hypomyelinating leukodystrophy. HSPD1 is cinically characterized by infantile-onset rotary nystagmus, progressive spastic paraplegia, neurologic regression, motor impairment, profound mental retardation. Death usually occurrs within the first two decades of life.
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