Huang Peggy, Gautschi Matthias, Walter William, Rospert Sabine, Craig Elizabeth A
Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
Nat Struct Mol Biol. 2005 Jun;12(6):497-504. doi: 10.1038/nsmb942. Epub 2005 May 22.
J-proteins are obligate partners of Hsp70s, forming a ubiquitous class of molecular chaperone machinery. The ribosome-associated Hsp70 of yeast Ssb binds nascent polypeptides as they exit the ribosome. Here we report that the ribosome-associated J-protein Zuo1 is the partner of Ssb. However, Zuo1 efficiently stimulates the ATPase activity of Ssb only when in complex with another Hsp70, Ssz1. Ssz1 binds ATP, but none of the 11 different amino acid substitutions in the ATP-binding cleft affected Ssz1 function in vivo, suggesting that neither nucleotide binding nor hydrolysis is required. We propose that Ssz1's predominant function in the cell is to facilitate Zuo1's ability to function as a J-protein partner of Ssb on the ribosome, serving as an example of an Hsp70 family member that has evolved to carry out functions distinct from that of a chaperone.
J蛋白是Hsp70的必需伴侣，构成了一类普遍存在的分子伴侣机制。酵母Ssb的核糖体相关Hsp70在新生多肽离开核糖体时与之结合。我们在此报告，核糖体相关J蛋白Zuo1是Ssb的伴侣。然而，只有在与另一种Hsp70即Ssz1形成复合物时，Zuo1才能有效地刺激Ssb的ATP酶活性。Ssz1结合ATP，但ATP结合裂隙中的11种不同氨基酸取代均未影响Ssz1在体内的功能，这表明核苷酸结合和水解均非必需。我们提出，Ssz1在细胞中的主要功能是促进Zuo1作为核糖体上Ssb的J蛋白伴侣发挥功能，这是一个Hsp70家族成员进化后执行不同于伴侣功能的例子。
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