Evolution of New Function in the GTP Cyclohydrolase II Proteins of Streptomyces coelicolor

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• 作者：James E. Spoonamore ; Annie L. Dahlgran ; Neil E. Jacobsen ; Vahe Bandarian
• 刊名：Biochemistry
• 出版年：2006
• 出版时间：October 3, 2006
• 年：2006
• 卷：45
• 期：39
• 页码：12144 - 12155
• 全文大小：389K
• 年卷期：v.45,no.39(October 3, 2006)
• ISSN：1520-4995

文摘

The genome sequence of Streptomyces coelicolor contains three open reading frames (sco1441,sco2687, and sco6655) that encode proteins with significant (>40%) amino acid identity to GTPcyclohydrolase II (GCH II), which catalyzes the committed step in the biosynthesis of riboflavin. Thephysiological significance of the redundancy of these proteins in S. coelicolor is not known. However,the gene contexts of the three proteins are different, suggesting that they may serve alternate biologicalniches. Each of the three proteins was overexpressed in Escherichia coli and characterized to determineif their functions are biologically overlapping. As purified, each protein contains 1 molar equiv of zinc/mol of protein and utilizes guanosine 5'-triphosphate (GTP) as substrate. Two of these proteins (SCO1441 and SCO 2687) produce the canonical product of GCH II, 2,5-diamino-6-ribosylamino-4(3H)-pyrimidinone 5'-phosphate (APy). Remarkably, however, one of the three proteins (SCO 6655) convertsGTP to 2-amino-5-formylamino-6-ribosylamino-4(3H)-pyrimidinone 5'-phosphate (FAPy), as shown byUV-visible spectrophotometry, mass spectrometry, and NMR. This activity has been reported for a GTPcyclohydrolase III protein from Methanocaldococcus jannaschii [Graham, D. E., Xu, H., and White, R.H. (2002) Biochemistry 41, 15074-15084], which has no amino acid sequence homology to SCO 6655.Comparison of the sequences of these proteins and mapping onto the structure of the E. coli GCH IIprotein [Ren, J., Kotaka, M., Lockyer, M., Lamb, H. K., Hawkins, A. R., and Stammers, D. K. (2005) J.Biol. Chem. 280, 36912-36919] allowed identification of a switch residue, Met120, which appears to beresponsible for the altered fate of GTP observed with SCO 6655; a Tyr is found in the analogous positionof all proteins that have been shown to catalyze the conversion of GTP to APy. The Met120Tyr variantof SCO 6655 acquires the ability to catalyze the conversion of GTP to APy, suggesting a role for Tyr120in the late phase of the reaction. Our data are consistent with duplication of GCH II in S. coelicolorpromoting evolution of a new function. The physiological role(s) of the gene clusters that house GCH IIhomologues will be discussed.