Treponema denticola PurE Is a Bacterial AIR Carboxylase

详细信息    查看全文

• 作者：Sylvain Tranchimand ; Courtney M. Starks ; Irimpan I. Mathews ; Susan C. Hockings ; T. Joseph Kappock
• 刊名：Biochemistry
• 出版年：2011
• 出版时间：May 31, 2011
• 年：2011
• 卷：50
• 期：21
• 页码：4623-4637
• 全文大小：1148K
• 年卷期：v.50,no.21(May 31, 2011)
• ISSN：1520-4995

文摘

De novo purine biosynthesis proceeds by two divergent paths. In bacteria, yeasts, and plants, 5-aminoimidazole ribonucleotide (AIR) is converted to 4-carboxy-AIR (CAIR) by two enzymes: N⁵-carboxy-AIR (N⁵-CAIR) synthetase (PurK) and N⁵-CAIR mutase (class I PurE). In animals, the conversion of AIR to CAIR requires a single enzyme, AIR carboxylase (class II PurE). The CAIR carboxylate derives from bicarbonate or CO₂, respectively. Class I PurE is a promising antimicrobial target. Class I and class II PurEs are mechanistically related but bind different substrates. The spirochete dental pathogen Treponema denticola lacks a purK gene and contains a class II purE gene, the hallmarks of CO₂-dependent CAIR synthesis. We demonstrate that T. denticola PurE (TdPurE) is AIR carboxylase, the first example of a prokaryotic class II PurE. Steady-state and pre-steady-state experiments show that TdPurE binds AIR and CO₂ but not N⁵-CAIR. Crystal structures of TdPurE alone and in complex with AIR show a conformational change in the key active site His40 residue that is not observed for class I PurEs. A contact between the AIR phosphate and a differentially conserved residue (TdPurE Lys41) enforces different AIR conformations in each PurE class. As a consequence, the TdPurE路AIR complex contains a portal that appears to allow the CO₂ substrate to enter the active site. In the human pathogen T. denticola, purine biosynthesis should depend on available CO₂ levels. Because spirochetes lack carbonic anhydrase, the corresponding reduction in bicarbonate demand may confer a selective advantage.