nucleotide-binding domain (NBD) of Saccharomyces cerevisiae ribosome-associated complex subunit Ssz1 and similar proteins
Ssz1, also called DnaK-related protein Ssz1, heat shock protein 70 homolog Ssz1, or pleiotropic drug resistance protein 13 (PDR13), is a component of the ribosome-associated complex (RAC), a heterodimeric chaperone complex involved in regulation of accurate translation termination and in folding or maintaining nascent polypeptides in a folding-competent state. RAC stimulates the ATPase activity of the ribosome-associated pool of Hsp70-type chaperones Ssb1/Ssb2 that bind to the nascent polypeptide chain. Ssz1 is required for Zuo1 to function efficiently as a J-protein for Ssb1/Ssb2. It is also involved in pleiotropic drug resistance by post-translational activation of transcription factor PDR1. Members in this subfamily belong to the heat shock protein 70 (HSP70) family of chaperones that assist in protein folding and assembly and can direct incompetent "client" proteins towards degradation. Typically, HSP70s have a nucleotide-binding domain (NBD) and a substrate-binding domain (SBD). 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.
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