Reaching for Mechanistic Consensus Across Life Kingdoms: Structure and Insights into Catalysis of the myo-Inositol-1-phosphate Synthase (mIPS) from Archaeoglobus fulgidus

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• 作者：Kimberly A. Stieglitz ; Hongying Yang ; Mary F. Roberts ; and Boguslaw Stec
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：January 11, 2005
• 年：2005
• 卷：44
• 期：1
• 页码：213 - 224
• 全文大小：790K
• 年卷期：v.44,no.1(January 11, 2005)
• ISSN：1520-4995

文摘

myo-Inositol-1-phosphate synthase (mIPS) catalyzes the first step in the synthesis of L-myo-inositol-1-phosphate. We have solved and refined the structure of the mIPS from the hyperthermophilicsulfate reducer Archaeoglobus fulgidus at 1.9 Å resolution. The enzyme crystallized from poly(ethyleneglycol) in the P1 space group with one tetramer in the asymmetric unit and provided a view of the entirebiologically active oligomer. Despite significant changes in sequence length and amino acid composition,the general architecture of the archaeal enzyme is similar to that of the eukaryotic mIPS from Saccharomycescerevisiae and bacterial mIPS from Mycobacterium tuberculosis. The enhanced thermostability of thearchaeal enzyme as compared to that from yeast is consistent with deletion of a number of surface loopsthat results in a significantly smaller protein. In the structure of the A. fulgidus mIPS, the active sites ofall four subunits were fully ordered and contained NAD⁺ and inorganic phosphate. The structure alsocontained a single metal ion (identified as K⁺) in two of the four subunits. The analysis of the electrostaticpotential maps of the protein suggested the presence of a second metal-ion-binding site in close proximityto the first metal ion and NAD⁺. The modeling of the substrate and known inhibitors suggests a criticalrole for the second metal ion in catalysis and provides insights into the common elements of the catalyticcycle in enzymes from different life kingdoms.