Biomedical subjects

T Quang

Publications and source records attributed to T Quang.

At least 19 recordsLinked to original sources

PubMed1998

Conformational changes in the cytoplasmic domain of the Escherichia coli aspartate receptor upon adaptive methylation.

By using targeted disulfide cross-linking, we have characterized structural changes that the Escherichia coli aspartate receptor undergoes upon modification of the four specific residues that are reversibly methylated during sensory adaptation. Cysteine residues were introduced at specific positions either in the cytoplasmic domain or in the periplasmic domain, and the rates of disulfide cross-linking were used to probe for conformational changes upon covalent modification. Conversion of the methylation sites from glutamates to glutamines greatly reduced the rate of disulfide formation between residues 265 and 265' and residues 250 and 250' in the cytoplasmic domain but not between residues 36 and 36' in the periplasmic domain. (Primes are used to indicate the second of the two identical subunits in the homologous dimer.) The covalent modification of the cytoplasmic domain induces conformational changes that are detectable in the cytoplasmic domain but none that are detectable in the periplasmic domain.

Amides↗

PubMed1997

Methylation of the Escherichia coli chemotaxis receptors: intra- and interdimer mechanisms.

The mechanism(s) of methylation of the Escherichia coli chemotaxis receptors was analyzed by experiments involving the construction of a series of aspartate receptor variants. Truncation of five or more residues from the C-terminal end of the aspartate receptor, which prevents the methyltransferase from binding to the receptor, resulted in very low rates of methylation, indicating that the methyltransferase is activated by binding to the receptor. Coexpression of a receptor variant that is unmethylatable but able to C-terminally bind the methyltransferase resulted in much higher methylation rates for all of the truncated receptors. By preventing the possibility of subunit exchange between receptor variants, we showed that the truncated receptors were methylated via an interdimer mechanism. The interdimer methylation rates of the truncated receptors were found to be 3-fold lower than the methylation rate of the unaltered receptor, suggesting that intradimer methylation as well as interdimer methylation accounts for the methylation of the unaltered receptor. In addition, the presence of the cytoplasmic signaling proteins, which have been shown to cause receptor clustering, did not influence the rates of methylation.

Amino Acid Sequence↗

PubMed1996