Substitution of Cadmium for Zinc in Farnesyl:Protein Transferase Alters Its Substrate Specificity

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• 作者：Fang L. Zhang ; Hua-Wen Fu ; Patrick J. Casey ; and W. Robert Bishop
• 刊名：Biochemistry
• 出版年：1996
• 出版时间：June 25, 1996
• 年：1996
• 卷：35
• 期：25
• 页码：8166 - 8171
• 全文大小：405K
• 年卷期：v.35,no.25(June 25, 1996)
• ISSN：1520-4995

文摘

Ras proteins are mutationally activated in a variety of humancancers. Since farnesylation ofRas proteins is required for expression of their oncogenic potential,the enzyme responsible for this reaction,farnesyl:protein transferase (FPT), has become a major target foranticancer drug development. FPT isa zinc metalloenzyme, and the zinc is essential for its catalyticactivity. To begin to elucidate the role ofzinc in catalysis, we initiated metal substitution studies. Of allmetals tested, only cadmium was able tofunctionally substitute for zinc, reconstituting enzymatic activitywith native substrates (H-Ras and farnesyldiphosphate) to about 50% of that of the zinc-containing enzyme.Several important differences wereobserved between cadmium-substituted FPT (Cd-FPT) and zinc-containingFPT (Zn-FPT). Cd-FPT notonly uses H-ras with its native CaaX motif (Ras-CVLS) as a substratebut also can farnesylate H-ras inwhich the CaaX motif is altered to contain a C-terminal leucine residue(Ras-CVLL). Similarly, Cd-FPTcan farnesylate leucine-terminated peptides. Leucine-terminatedproteins and peptides are usually substratesfor the related enzyme geranylgeranyl:protein transferase type I.Farnesylation of Ras-CVLS and Ras-CVLL by Cd-FPT exhibited similar sensitivity to the FPT inhibitor SCH44342 and to the peptide inhibitorCAIM. However, unlike Zn-FPT, Cd-FPT is also potently inhibited bythe leucine-terminated peptideCAIL. These results indicate that the metal ion content of FPTstrongly influences its protein substratespecificity.