A single amino acid substitution in the active site of Escherichia coli aspartate transcarbamoylase prevents the allosteric transition.

ABSTRACT: Modeling of the tetrahedral intermediate within the active site of Escherichia coli aspartate transcarbamoylase revealed a specific interaction with the side-chain of Gln137, an interaction not previously observed in the structure of the X-ray enzyme in the presence of N-phosphonacetyl-L-aspartate (PALA). Previous site-specific mutagenesis experiments showed that when Gln137 was replaced by alanine, the resulting mutant enzyme (Q137A) exhibited approximately 50-fold less activity than the wild-type enzyme, exhibited no homotropic cooperativity, and the binding of both carbamoyl phosphate and aspartate were extremely compromised. To elucidate the structural alterations in the mutant enzyme that might lead to such pronounced changes in kinetic and binding properties, the Q137A enzyme was stu

SUBMITTER: Stieglitz KA 

PROVIDER: S-EPMC1479453 | biostudies-literature | 2005 Jun

REPOSITORIES: biostudies-literature