Pseudomonas aeruginosa contains a novel type V porphobilinogen synthase with no required catalytic metal ions.
Pseudomonas aeruginosa contains a novel type V porphobilinogen synthase with no required catalytic metal ions.
复制标题
铜绿假单胞菌含有一种新型 V 型胆色素原合酶，无需催化金属离子。
DOI：
10.1021/bi9906470
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发表时间：
1999
期刊：
影响因子：
2.9
通讯作者：
Jaffe,EK
中科院分区：
文献类型：
--
作者：
Frankenberg,N;Jahn,D;Jaffe,EK
胆色素原合酶 (PBGS) 是催化四吡咯生物合成第一个常见步骤的金属酶。 PBGS 酶先前已根据在称为 A、B 和 C 的三个不同金属结合位点处利用的 Zn2+ 和/或 Mg2+ 的数量分为四种类型 (I−IV)。在这项研究中，发现铜绿假单胞菌 PBGS 在存在或不存在底物/产物的情况下，通过原子吸收光谱法测定，每个八聚体仅结合 4 个 Mg2+。这是迄今为止发现的 PBGS 结合金属离子的最低数量，而其他酶则结合 8−16 个二价离子。这四种 Mg2+ 以取决于 pH 和 K+ 的方式变构地刺激金属离子独立的催化活性。 PBGS 的变构 Mg2+ 位于金属结合位点 C，位于活性位点之外。没有发现金属与潜在的高亲和力活性位点金属结合位点 A 和/或 B.P 结合的证据。使用Mn2+作为Mg2+的EPR探针研究铜绿假单胞菌PBGS，并使用[3,5-13C]胆色素原作为NMR探针研究活性位点。磁共振数据排除了 Mg2+ 在底物结合和产物形成中的直接参与。综合数据表明 P. aeruginosaPBGS 代表一种新型 V 型酶。 V型PBGS具有以不依赖于金属离子的方式合成胆色素原的卓越能力。每个八聚体仅 4 个总金属离子化学计量表明半位点反应性。
Porphobilinogen synthases (PBGS) are metalloenzymes that catalyze the first common step in tetrapyrrole biosynthesis. The PBGS enzymes have previously been categorized into four types (I−IV) by the number of Zn2+and/or Mg2+utilized at three different metal binding sites termed A, B, and C. In this studyPseudomonas aeruginosaPBGS is found to bind only four Mg2+per octamer as determined by atomic absorption spectroscopy, in the presence or absence of substrate/product. This is the lowest number of bound metal ions yet found for PBGS where other enzymes bind 8−16 divalent ions. These four Mg2+allosterically stimulate a metal ion independent catalytic activity, in a fashion dependent upon both pH and K+. The allosteric Mg2+of PBGS is located in metal binding site C, which is outside the active site. No evidence is found for metal binding to the potential high-affinity active site metal binding sites A and/or B.P. aeruginosaPBGS was investigated using Mn2+as an EPR probe for Mg2+, and the active site was investigated using [3,5-13C]porphobilinogen as an NMR probe. The magnetic resonance data exclude the direct involvement of Mg2+in substrate binding and product formation. The combined data suggest thatP. aeruginosaPBGS represents a new type V enzyme. Type V PBGS has the remarkable ability to synthesize porphobilinogen in a metal ion independent fashion. The total metal ion stoichiometry of only 4 per octamer suggests half-sites reactivity.