Department of Life Science, Graduate School of Science, University of Hyogo, 3-2-1 Koto, Kamigori-cho, Ako-gun, Hyogo, 678-1297, Japan.
Institute of Organic Chemistry and, Center of Molecular Biosciences, University of Innsbruck, 6020, Innsbruck, Austria.
Chemistry. 2022 Nov 21;28(65):e202202196. doi: 10.1002/chem.202202196. Epub 2022 Sep 19.
The X-ray structures of coenzyme B (AdoCbl)-dependent eliminating isomerases complexed with adenosylmethylcobalamin (AdoMeCbl) have been determined. As judged from geometries, the Co-C bond in diol dehydratase (DD) is not activated even in the presence of substrate. In ethanolamine ammonia-lyase (EAL), the bond is elongated in the absence of substrate; in the presence of substrate, the complex likely exists in both pre- and post-homolysis states. The impacts of incorporating an extra CH group are different in the two enzymes: the DD active site is flexible, and AdoMeCbl binding causes large conformational changes that make DD unable to adopt the catalytic state, whereas the EAL active site is rigid, and AdoMeCbl binding does not induce significant conformational changes. Such flexibility and rigidity of the active sites might reflect the tightness of adenine binding. The structures provide good insights into the basis of the very low activity of AdoMeCbl in these enzymes.
已确定辅酶 B（AdoCbl）依赖性消除异构酶与腺苷甲硫氨酸钴胺素（AdoMeCbl）复合物的 X 射线结构。从几何形状判断，二醇脱水酶（DD）中的 Co-C 键即使在存在底物的情况下也未被激活。在乙醇胺氨裂解酶（EAL）中，不存在底物时键被拉长；存在底物时，该复合物可能存在于预均裂和后均裂两种状态。在这两种酶中，引入额外 CH 基团的影响不同：DD 活性位点灵活，AdoMeCbl 结合会导致构象发生巨大变化，使 DD 无法采用催化状态，而 EAL 活性位点刚性，AdoMeCbl 结合不会引起显著的构象变化。这些活性位点的灵活性和刚性可能反映了腺嘌呤结合的紧密程度。这些结构为阐明这些酶中 AdoMeCbl 极低活性的基础提供了很好的见解。
