Martin David P, Blachly Patrick G, Marts Amy R, Woodruff Tessa M, de Oliveira César A F, McCammon J Andrew, Tierney David L, Cohen Seth M
Department of Chemistry and Biochemistry, §Pharmacology, and ∥Howard Hughes Medical Institute, University of California, San Diego , La Jolla, California 92093, United States.
J Am Chem Soc. 2014 Apr 9;136(14):5400-6. doi: 10.1021/ja500616m. Epub 2014 Mar 27.
The binding of three closely related chelators: 5-hydroxy-2-methyl-4H-pyran-4-thione (allothiomaltol, ATM), 3-hydroxy-2-methyl-4H-pyran-4-thione (thiomaltol, TM), and 3-hydroxy-4H-pyran-4-thione (thiopyromeconic acid, TPMA) to the active site of human carbonic anhydrase II (hCAII) has been investigated. Two of these ligands display a monodentate mode of coordination to the active site Zn(2+) ion in hCAII that is not recapitulated in model complexes of the enzyme active site. This unprecedented binding mode in the hCAII-thiomaltol complex has been characterized by both X-ray crystallography and X-ray spectroscopy. In addition, the steric restrictions of the active site force the ligands into a 'flattened' mode of coordination compared with inorganic model complexes. This change in geometry has been shown by density functional computations to significantly decrease the strength of the metal-ligand binding. Collectively, these data demonstrate that the mode of binding by small metal-binding groups can be significantly influenced by the protein active site. Diminishing the strength of the metal-ligand bond results in unconventional modes of metal coordination not found in typical coordination compounds or even carefully engineered active site models, and understanding these effects is critical to the rational design of inhibitors that target clinically relevant metalloproteins.
5-羟基-2-甲基-4H-吡喃-4-硫酮（别硫麦芽酚，ATM）、3-羟基-2-甲基-4H-吡喃-4-硫酮（硫麦芽酚，TM）和3-羟基-4H-吡喃-4-硫酮（硫焦袂康酸，TPMA）与人碳酸酐酶II（hCAII）活性位点的结合情况。其中两种配体对hCAII活性位点的Zn(2+)离子呈现单齿配位模式，这在该酶活性位点的模型配合物中并未出现。hCAII - 硫麦芽酚复合物中这种前所未有的结合模式已通过X射线晶体学和X射线光谱学进行了表征。此外，与无机模型配合物相比，活性位点的空间限制迫使配体进入“扁平”配位模式。密度泛函计算表明，这种几何结构的变化显著降低了金属 - 配体结合的强度。总体而言，这些数据表明，小金属结合基团的结合模式会受到蛋白质活性位点的显著影响。金属 - 配体键强度的减弱导致了在典型配位化合物甚至精心设计的活性位点模型中都未发现的非常规金属配位模式，而理解这些效应对于合理设计靶向临床相关金属蛋白的抑制剂至关重要。
