Grant G A, Xu X L, Hu Z
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, 63110, USA.
Arch Biochem Biophys. 2000 Mar 1;375(1):171-4. doi: 10.1006/abbi.1999.1652.
Escherichia coli d-3-phosphoglycerate dehydrogenase (PGDH) is a homotetrameric enzyme whose activity is allosterically regulated by l-serine, the end-product of its metabolic pathway. Previous studies have shown that PGDH displays two modes of cooperative interaction. One is between the l-serine binding sites and the other is between the l-serine binding sites and the active sites. Tryptophan 139 participates in an intersubunit contact near the active site catalytic residues. Site-specific mutagenesis of tryptophan 139 to glycine results in the dissociation of the tetramer to a pair of dimers and in the loss of cooperativity in serine binding and between serine binding and inhibition. The results suggest that the magnitude of inhibition of activity at a particular active site is primarily dependent on serine binding to that subunit but that activity can be modulated in a cooperative manner by interaction with adjacent subunits. The disruption of the nucleotide domain interface in PGDH by mutating Trp-139 suggests the potential for a critical role of this interface in the cooperative allosteric processes in the native tetrameric enzyme.
大肠杆菌d-3-磷酸甘油酸脱氢酶（PGDH）是一种同四聚体酶，其活性受到其代谢途径终产物L-丝氨酸的变构调节。先前的研究表明，PGDH表现出两种协同相互作用模式。一种是在L-丝氨酸结合位点之间，另一种是在L-丝氨酸结合位点与活性位点之间。色氨酸139参与活性位点催化残基附近的亚基间接触。将色氨酸139定点突变为甘氨酸会导致四聚体解离为一对二聚体，并导致丝氨酸结合以及丝氨酸结合与抑制之间的协同性丧失。结果表明，特定活性位点处活性的抑制程度主要取决于丝氨酸与该亚基的结合，但活性可以通过与相邻亚基的相互作用以协同方式进行调节。通过突变Trp-139破坏PGDH中的核苷酸结构域界面，表明该界面在天然四聚体酶的协同变构过程中可能起关键作用。
