Binda Claudia, Li Min, Hubalek Frantisek, Restelli Nadia, Edmondson Dale E, Mattevi Andrea
Department of Genetics and Microbiology, University of Pavia, Via Abbiategrasso, 27100 Pavia, Italy.
Proc Natl Acad Sci U S A. 2003 Aug 19;100(17):9750-5. doi: 10.1073/pnas.1633804100. Epub 2003 Aug 11.
Monoamine oxidase B (MAO-B) is an outer mitochondrial membrane-bound enzyme that catalyzes the oxidative deamination of arylalkylamine neurotransmitters and has been a target for a number of clinically used drug inhibitors. The 1.7-A structure of the reversible isatin-MAO-B complex has been determined; it forms a basis for the interpretation of the enzyme's structure when bound to either reversible or irreversible inhibitors. 1,4-Diphenyl-2-butene is found to be a reversible MAO-B inhibitor, which occupies both the entrance and substrate cavity space in the enzyme. Comparison of these two structures identifies Ile-199 as a "gate" between the two cavities. Rotation of the side chain allows for either separation or fusion of the two cavities. Inhibition of the enzyme with N-(2-aminoethyl)-p-chlorobenzamide results in the formation of a covalent N(5) flavin adduct with the phenyl ring of the inhibitor occupying a position in the catalytic site overlapping that of isatin. Inhibition of MAO-B with the clinically used trans-2-phenylcyclopropylamine results in the formation of a covalent C(4a) flavin adduct with an opened cyclopropyl ring and the phenyl ring in a parallel orientation to the flavin. The peptide bond between the flavin-substituted Cys-397 and Tyr-398 is in a cis conformation, which allows the proper orientation of the phenolic ring of Tyr-398 in the active site. The flavin ring exists in a twisted nonplanar conformation, which is observed in the oxidized form as well as in both the N(5) and the C(4a) adducts. An immobile water molecule is H-bonded to Lys-296 and to the N(5) of the flavin as observed in other flavin-dependent amine oxidases. The active site cavities are highly apolar; however, hydrophilic areas exist near the flavin and direct the amine moiety of the substrate for binding and catalysis. Small conformational changes are observed on comparison of the different inhibitor-enzyme complexes. Future MAO-B drug design will need to consider "induced fit" contributions as an element in ligand-enzyme interactions.
单胺氧化酶B（MAO - B）是一种线粒体外膜结合酶，可催化芳基烷基胺神经递质的氧化脱氨反应，并且一直是许多临床使用的药物抑制剂的作用靶点。已确定了可逆性异吲哚酮 - MAO - B复合物的1.7埃结构；它为解释该酶与可逆或不可逆抑制剂结合时的结构奠定了基础。发现1,4 - 二苯基 - 2 - 丁烯是一种可逆性MAO - B抑制剂，它占据了该酶的入口和底物腔空间。这两种结构的比较确定异亮氨酸 - 199是两个腔之间的“门”。侧链的旋转允许两个腔分离或融合。用N -（2 - 氨基乙基）-对氯苯甲酰胺抑制该酶会导致形成一种共价N（5）黄素加合物，抑制剂的苯环占据催化位点中与异吲哚酮重叠的位置。用临床使用的反式 - 2 - 苯基环丙胺抑制MAO - B会导致形成一种共价C（4a）黄素加合物，其中环丙基环打开，苯环与黄素呈平行取向。黄素取代的半胱氨酸 - 397和酪氨酸 - 398之间的肽键呈顺式构象，这使得酪氨酸 - 398的酚环在活性位点具有正确的取向。黄素环以扭曲的非平面构象存在，在氧化形式以及N（5）和C（4a）加合物中均观察到这种构象。如在其他黄素依赖性胺氧化酶中所观察到的，一个固定的水分子通过氢键与赖氨酸 - 296和黄素的N（5）相连。活性位点腔是高度非极性的；然而，在黄素附近存在亲水区域，可引导底物的胺部分进行结合和催化。在比较不同的抑制剂 - 酶复合物时观察到了小的构象变化。未来MAO - B药物设计将需要考虑“诱导契合”作用，将其作为配体 - 酶相互作用中的一个要素。
