X-ray Crystal Structures of the S229A Mutant and Wild-Type MurB in the Presence of the Substrate Enolpyruvyl-UDP-N-Acetylglucosamine at 1.8-Å Resolution

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• 作者：Timothy E. Benson ; Christopher T. Walsh ; and James M. Hogle
• 刊名：Biochemistry
• 出版年：1997
• 出版时间：January 28, 1997
• 年：1997
• 卷：36
• 期：4
• 页码：806 - 811
• 全文大小：402K
• 年卷期：v.36,no.4(January 28, 1997)
• ISSN：1520-4995

文摘

MurB catalyzes the second committed step in the synthesis ofpeptidoglycan, a key componentof the bacterial cell wall. The crystal structures of both a S229Amutant and wild-type MurB in thepresence of the substrateenolpyruvyl-UDP-N-acetylglucosamine were solved and refinedat 1.8 Å resolution.The single point mutation of residue 229 from serine to alanineeliminated a hydroxyl group which haspreviously been proposed to play a critical role as a proton donorduring the second half-reaction ofMurB, namely, reoxidation of FADH₂ and reduction of theenolpyruvyl substrate. The mutation alsoresulted in the loss of the water molecule-hydrogen bonded to theserine hydroxyl in the wild-type structurechanging the hydrogen-bonding network with in the active site.Comparison of the wild-type and S229Amutant structures confirms that the dramatic kinetic defect of anapproximately 10⁷-fold decrease observedfor the Ser 229 Ala mutant in the second half-reaction [Benson, T. E.,Walsh, C. T., & Massey, V. (1997)Biochemistry 36, 796-805] is a direct result of the lossof the serine hydroxyl moiety rather than othernonspecific active-site changes or general structuraldefects.