Understanding Functional Divergence in Proteins by Studying Intragenomic Homologues

详细信息    查看全文

• 作者：James E. Spoonamore ; Vahe Bandarian
• 刊名：Biochemistry
• 出版年：2008
• 出版时间：February 26, 2008
• 年：2008
• 卷：47
• 期：8
• 页码：2592 - 2600
• 全文大小：364K
• 年卷期：v.47,no.8(February 26, 2008)
• ISSN：1520-4995

文摘

Studies of intragenomic homologues in bacterial genomes can provide valuable insights intofunctional divergence. Three GTP cyclohydrolase II homologues in the Streptomyces coelicolor genomehave been shown to catalyze two related but distinct reactions [Spoonamore, J. E., Dahlgran, A. L., Jacobsen,N. E., and Bandarian, V. (2006) Biochemistry 45, 12144-12155]. Two of the homologues, SCO 1441and 2687, convert GTP to 2,5-diamino-6-ribosylamino-4(3H)-pyrimidinone 5'-phosphate (APy); one ofthe homologues (SCO 6655) produces 2-amino-5-formylamino-6-ribosylamino-4(3H)-pyrimidinone 5'-phosphate (FAPy). We show herein that the differences in the fate of GTP in SCO 6655 relative to SCO1441 and 2687 results from a single amino acid substitution in the active site of the protein: a Tyr residuein the active sites of SCO 1441 and SCO 2687 is replaced with a Met in SCO 6655. Site-directed interchangeof this residue in the three S. coelicolor intragenomic homologues is necessary and sufficient forinterconversion of catalytic function which, except for SCO 1441, occurs with little loss of catalyticefficiency. Furthermore, we show that of 14 additional site-directed variants at this position of SCO 6655,His confers catalytic efficiency within 1 order of magnitude of that of the wild type and supports conversionof GTP to both FAPy and APy. The results demonstrate a clear set of mutational events that permit GCHII to produce either FAPy or APy. These results highlight a mechanism whereby functional divergencecan be achieved in enzymes that catalyze multistep transformations.