nucleotide-binding domain (NBD) of the heat shock 70 kDa protein 4 (HSPA4)-like subfamily
This subgroup includes the human proteins, HSPA4 (also known as 70-kDa heat shock protein 4; APG-2; HS24/P52; hsp70 RY; HSPH2), HSPA4L (also known as 70-kDa heat shock protein 4-like; APG-1; HSPH3; OSP94), and HSPH1 (also known as heat shock 105kDa/110kDa protein 1; HSP105; HSP105A; HSP105B; NY-CO-25). They belong to the 105/110 kDa heat shock protein (HSP105/110) subfamily of the HSP70-like family, and includes proteins believed to function generally as co-chaperones of HSP70 chaperones, acting as nucleotide exchange factors (NEFs), to remove ADP from their HSP70 chaperone partners during the ATP hydrolysis cycle. HSP70 chaperones assist in protein folding and assembly, and can direct incompetent "client" proteins towards degradation. Like HSP70 chaperones, HSP105/110s have an N-terminal nucleotide-binding domain (NBD) and a C-terminal substrate-binding domain (SBD). For HSP70 chaperones, the nucleotide sits in a deep cleft formed between the two lobes of the NBD. The two subdomains of each lobe change conformation between ATP-bound, ADP-bound, and nucleotide-free states. ATP binding opens up the substrate-binding site; substrate-binding increases the rate of ATP hydrolysis. Hsp70 chaperone activity is also regulated by J-domain proteins.
Jiyao W et al.(2023). "The conserved domain database in 2023.",