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The function and evolution of the yeast prion protein Ure2

张在荣  Sarah Perrett  
【摘要】:正Ure2 is the protein determinant of the yeast prion [URE3].It is composed of two regions,the N-terrninal prion domain and the C-terminal glutathione transferase (GST)-like domain,which shows similarity to the GST enzyme family in both sequence and structure.Ure2 protects Saccharomyces cerevisiae cells from heavy metal ion and oxidant toxicity and possesses a low level of glutathione-dependent peroxidase (GPx) activity,which is often an adjunct activity of GST enzymes, but Ure2 shows no detectable GST activity toward the standard substrate 1-chloro-2,4-dinitrobenzene (CDNB).The structural basis for the substrate specificity of Ure2 enzymatic activity and its relationship to the GST structural family is an interesting problem which is fundamental to understanding the in vivo roles of Ure2.We observed detectable GST activity toward CDNB for certain Ure2 mutants,including A122C,N124A,and N124V.The mutant A122C shows a different steady-state reaction mechanism from that of 124-site mutants,implying a potential capacity of Ure2 to show classical CaST activity and demonstrating the"mechanistic promiscuity"of Ure2.These findings help elucidate the evolutionary relationship of Ure2 with other GST family members and contribute to our understanding of catalytic promiscuity and divergent evolution.

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