Khrustalev Vladislav Victorovich, Barkovsky Eugene Victorovich, Khrustaleva Tatyana Aleksandrovna
Department of General Chemistry, Belarusian State Medical University, Dzerzinskogo, 83, Minsk, Belarus.
Department of General Chemistry, Belarusian State Medical University, Dzerzinskogo, 83, Minsk, Belarus.
J Theor Biol. 2016 Apr 21;395:174-185. doi: 10.1016/j.jtbi.2016.02.006. Epub 2016 Feb 11.
Manganese ion (Mn(2+)) can substitute magnesium ion (Mg(2+)) in active sites of numerous enzymes. Binding sites for these two ions have been studied in two sets of protein 3D structures from the Protein Data Bank with the homology level lower than 25%. The structural motif "beta strand - binder - random coil" is predominant in both Mn(2+) and Mg(2+) coordination spheres, especially in functionally relevant ones. That predominant motif works as an active binder of those divalent cations which can then attract additional ligands, such as different phosphate-containing compounds. In contrast, such Mg(2+) and Mn(2+) binding motif as "GK(T/S)T" being the N-terminal part of alpha helices works as an active binder of phosphates which can then attract divalent cations. There are few differences between Mg(2+) and Mn(2+) coordination spheres responsible of the cation specificity. His residues are underrepresented in certain positions around Asp and Glu residues involved in Mg(2+) coordination, while they are overrepresented in certain positions around Asp and Glu residues coordinating Mn(2+). The random coil region in the "beta strand - random coil - alpha helix" motif for Mg(2+) binding is usually shorter than that in the same motif for Mn(2+) coordination. This feature is associated with the lower number of binding amino acids (and lower levels of usage of such "major" binders as Asp and Glu) for Mg(2+) (which is a hard Lewis acid) in comparison with those for Mn(2+) (an intermediate Lewis acid).
锰离子（Mn(2+)）可在众多酶的活性位点替代镁离子（Mg(2+)）。已从蛋白质数据库中同源性低于25%的两组蛋白质三维结构研究了这两种离子的结合位点。“β链 - 结合剂 - 无规卷曲”结构基序在Mn(2+)和Mg(2+)的配位球中均占主导，尤其是在功能相关的配位球中。该主导结构基序作为这些二价阳离子的活性结合剂，进而能吸引其他配体，如不同的含磷化合物。相比之下，作为α螺旋N端部分的“GK(T/S)T”这种Mg(2+)和Mn(2+)结合基序则作为磷酸盐的活性结合剂，随后能吸引二价阳离子。负责阳离子特异性的Mg(2+)和Mn(2+)配位球之间存在一些差异。在参与Mg(2+)配位的Asp和Glu残基周围的某些位置，His残基含量不足，而在配位Mn(2+)的Asp和Glu残基周围的某些位置，His残基含量过高。Mg(2+)结合的“β链 - 无规卷曲 - α螺旋”基序中的无规卷曲区域通常比Mn(2+)配位的相同基序中的短。与Mn(2+)（一种中等强度的路易斯酸）相比，这一特征与Mg(2+)（一种硬路易斯酸）结合氨基酸数量较少（以及Asp和Glu等“主要”结合剂的使用水平较低）有关。
