磷酸甘露糖异构酶的结构和功能见解：锌和催化残基的作用。,Acta Crystallographica Section D

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磷酸甘露糖异构酶的结构和功能见解：锌和催化残基的作用。
Acta Crystallographica Section D ( IF 2.6 ) Pub Date : 2019-05-07 , DOI: 10.1107/s2059798319004169
Mamata Bangera ₁ , Giri Gowda K ₁ , S R Sagurthi ₁ , M R N Murthy ₁

Affiliation

磷酸甘露糖异构酶（PMI）是一种看家酶，广泛存在于从细菌，真菌到哺乳动物的各种生物中，并且对于细胞壁合成，生存力和信号传导至关重要。PMI是一种锌依赖性酶，可催化甘露糖6磷酸（M6P）和果糖6磷酸（F6P）之间的可逆异构化，可能是通过形成顺式烯二醇中间体。假设该反应涉及M6P的开环，质子从C2原子转移到C1原子以及在底物的O1和O2原子之间转移，然后闭环产生产物F6P。已经进行了一些尝试来解释锌离子和各种残基在PMI催化功能中的作用。但是，关于催化碱和酶催化反应的机理尚无共识。在本研究中，基于鼠伤寒沙门氏菌的PMI结构，针对靠近结合金属离子的残基的定点诱变和突变体活性研究表明，锌离子对于底物结合至关重要。这些研究还表明，Lys86是最有可能在异构化反应中提取质子的催化碱基。通过比较野生型和突变型PMI的晶体结构，也可以发现高度保守的残基Lys132和Arg274的合理作用。来自原核生物的PMI与人类酶具有低序列同一性，介于30％至40％之间。由于PMI对于许多病原生物的毒性至关重要，因此识别具有催化作用的残留物将有助于将其用作潜在的抗菌药物靶标。

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Structural and functional insights into phosphomannose isomerase: the role of zinc and catalytic residues.

Phosphomannose isomerase (PMI) is a housekeeping enzyme that is found in organisms ranging from bacteria to fungi to mammals and is important for cell‐wall synthesis, viability and signalling. PMI is a zinc‐dependent enzyme that catalyses the reversible isomerization between mannose 6‐phosphate (M6P) and fructose 6‐phosphate (F6P), presumably via the formation of a cis‐enediol intermediate. The reaction is hypothesized to involve ring opening of M6P, the transfer of a proton from the C2 atom to the C1 atom and between the O1 and O2 atoms of the substrate, followed by ring closure resulting in the product F6P. Several attempts have been made to decipher the role of zinc ions and various residues in the catalytic function of PMI. However, there is no consensus on the catalytic base and the mechanism of the reaction catalyzed by the enzyme. In the present study, based on the structure of PMI from Salmonella typhimurium, site‐directed mutagenesis targeting residues close to the bound metal ion and activity studies on the mutants, zinc ions were shown to be crucial for substrate binding. These studies also suggest Lys86 as the most probable catalytic base abstracting the proton in the isomerization reaction. Plausible roles for the highly conserved residues Lys132 and Arg274 could also be discerned based on comparison of the crystal structures of wild‐type and mutant PMIs. PMIs from prokaryotes possess a low sequence identity to the human enzyme, ranging between 30% and 40%. Since PMI is important for the virulence of many pathogenic organisms, the identification of catalytically important residues will facilitate its use as a potential antimicrobial drug target.

更新日期：2019-05-07

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