Reaction Coupling through Interdomain Contacts in Imidazole Glycerol Phosphate Synthase

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• 作者：Rebecca S. Myers ; Rommie E. Amaro ; Zaida A. Luthey-Schulten ; and V. Jo Davisson
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：September 13, 2005
• 年：2005
• 卷：44
• 期：36
• 页码：11974 - 11985
• 全文大小：764K
• 年卷期：v.44,no.36(September 13, 2005)
• ISSN：1520-4995

文摘

Imidazole glycerol phosphate (IGP) synthase, a triad glutamine amidotransferase, catalyzesthe fifth step in the histidine biosynthetic pathway, where ammonia from glutamine is incorporated intoN¹-[(5'-phosphoribulosyl)-formimino]-5-aminoimidazole-4-carboxamide ribonucleotide (PRFAR) to yieldIGP and 5'-(5-aminoimidazole-4-carboxamide) ribonucleotide (AICAR). The triad family of glutamineamidotransferases is formed by the coupling of two disparate subdomains, an acceptor domain and aglutamine hydrolysis domain. Each of the enzymes in this family share a common glutaminase domainfor which the glutaminase activity is tightly regulated by an acceptor substrate domain. In IGP synthasethe glutaminase and PRFAR binding sites are separated by 30 Å. Using kinetic analyses of site-specificmutants and molecular dynamic simulations, we have determined that an interdomain salt bridge in IGPsynthase between D359 and K196 (approximately 16 Å from the PRFAR binding site) plays a key rolein mediating communication between the two active sites. This interdomain contact modulates theglutaminase loop containing the histidine and glutamic acid of the catalytic triad to control glutaminehydrolysis. We propose this to be a general principle of catalytic coupling that may be applied to theentire triad glutamine amidotransferase family.