Craescu C T, Schaad O, Garel M C, Rosa R, Edelstein S
Institut National de la Santé et de la Recherche Médicale U91, Hôpital Henri Mondor, Créteil, France.
Biochimie. 1992 Jun;74(6):519-26. doi: 10.1016/0300-9084(92)90149-9.
Using the crystallographic structure of yeast monophosphoglycerate mutase (MPGM) as a framework we constructed a three-dimensional model of the homologous human erythrocyte bisphosphoglycerate mutase (BPGM). The modeling procedure consisted of substituting 117 amino acid residues and positioning 19 C-terminal residues (unresolved in the X-ray structure) by empirical methods, followed by energy minimization. Among several differences in the active site region the most significant appears to be the replacement of Ser11 in MPGM by Gly in BPGM. The C-terminal segment, which contains mainly basic amino acids, lines the cavity of the active site. The seven amino acid residues, which have been shown to be essential for the three catalytic functions of the human BPGM, interact with the amino acids in the protein core, near the active site. In addition, a cluster of several positively charged residues, particularly arginines, has been identified at the entrance of the active site; this cluster may serve as a secondary binding site for polyanionic substrates or cofactors, as required by a two-binding-site model of the catalytic activities. This model is in agreement with recent studies of an inactive BPGM variant substituent at an Arg position situated in this positively charged cluster. The position of Cys20 in the model constructed suggests that this residue is responsible for inactivation of the enzyme by sulfhydryl reagents. Subunit interfaces have also been constructed for BPGM by analogy with MPGM and suggest that, in addition to the known dimerization of BPGM, tetramerization may occur under certain conditions.
以酵母单磷酸甘油酸变位酶（MPGM）的晶体结构为框架，我们构建了同源的人红细胞双磷酸甘油酸变位酶（BPGM）的三维模型。建模过程包括通过经验方法替换117个氨基酸残基并定位19个C末端残基（X射线结构中未解析），然后进行能量最小化。在活性位点区域的几个差异中，最显著的似乎是BPGM中Gly取代了MPGM中的Ser11。主要包含碱性氨基酸的C末端片段排列在活性位点的腔内。已证明对人BPGM的三种催化功能至关重要的七个氨基酸残基与活性位点附近蛋白质核心中的氨基酸相互作用。此外，在活性位点入口处已鉴定出几个带正电荷的残基簇，特别是精氨酸；根据催化活性的双结合位点模型，该簇可能作为多阴离子底物或辅因子的二级结合位点。该模型与最近对位于该带正电荷簇中的Arg位置的无活性BPGM变体取代基的研究一致。构建的模型中Cys20的位置表明该残基负责巯基试剂使酶失活。还通过类比MPGM构建了BPGM的亚基界面，表明除了已知的BPGM二聚化外，在某些条件下可能会发生四聚化。
