nucleotide-binding domain (NBD) of Arabidopsis thaliana heat shock 70 kDa protein 14-16 and similar proteins
The subgroup includes Arabidopsis thaliana Hsp70-14, also known as heat shock 70 kDa protein 14; heat shock protein 91), Hsp70-15 (also known as heat shock 70 kDa protein 15), and Hsp70-16 (also known as heat shock 70 kDa protein 16). In cooperation with other chaperones, they are key components that facilitate folding of de novo synthesized proteins, assist translocation of precursor proteins into organelles, and are responsible for degradation of damaged protein under stress conditions. Members in this subgroup 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.
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