期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 282, 期 16, 页码 11941-11949出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M611328200
关键词
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资金
- NIGMS NIH HHS [GM52470] Funding Source: Medline
Triphosphate tunnel metalloenzymes ( TTMs) are a newly recognized superfamily of phosphotransferases defined by a unique active site residing within an eight-stranded beta barrel. The prototypical members are the eukaryal metal-dependent RNA triphosphatases, which catalyze the initial step in mRNA capping. Little is known about the activities and substrate specificities of the scores of TTM homologs present in bacterial and archaeal proteomes, nearly all of which are annotated as adenylate cyclases. Here we have conducted a biochemical and structure-function analysis of a TTM protein ( CthTTM) from the bacterium Clostridium thermocellum. CthTTM is a metal-dependent tripolyphosphatase and nucleoside triphosphatase; it is not an adenylate cyclase. We have identified 11 conserved amino acids in the tunnel that are critical for tripolyphosphatase and ATPase activity. The most salient findings are that ( i) CthTTM is 150-fold more active in cleaving tripolyphosphate than ATP and ( ii) the substrate specificity of CthTTM can be transformed by a single mutation ( K8A) that abolishes tripolyphosphatase activity while strongly stimulating ATP hydrolysis. Our results underscore the plasticity of CthTTM substrate choice and suggest how novel specificities within the TTM superfamily might evolve through changes in the residues that line the tunnel walls.
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