PubMed Health⌕ Search

Biomedical subjects

W C Copeland

Publications and source records attributed to W C Copeland.

39 records · Page 3Linked to original sources
PubMed1986

Cloning and nucleotide sequence of wild type and a mutant histidine decarboxylase from Lactobacillus 30a.

Prohistidine decarboxylase from Lactobacillus 30a is a protein that autoactivates to histidine decarboxylase by cleaving its peptide chain between serines 81 and 82 and converting Ser-82 to a pyruvoyl moiety. The pyruvoyl group serves as the prosthetic group for the decarboxylation reaction. We have cloned and determined the nucleotide sequence of the gene for this enzyme from a wild type strain and from a mutant with altered autoactivation properties. The nucleotide sequence modifies the previously determined amino acid sequence of the protein. A tripeptide missed in the chemical sequence is inserted, and three other amino acids show conservative changes. The activation mutant shows a single change of Gly-58 to an Asp. Sequence analysis up- and downstream from the gene suggests that histidine decarboxylase is part of a polycistronic message, and that the transcriptional promotor region is strongly homologous to those of other Gram-positive organisms.

Amino Acid Sequence↗
PubMedDate not supplied

Expression and characterization of Lactobacillus 30a histidine decarboxylase in Escherichia coli.

The genes coding for histidine decarboxylase from a wild-type strain and an autoactivation mutant strain of Lactobacillus 30a have been cloned and expressed in Escherichia coli. The mutant protein, G58D, has a single Asp for Gly substitution at position 58. The cloned genes were placed under control of the beta-galactosidase promoter and the products are natural length, not fusion proteins. The enzyme kinetics of the proteins isolated from E. coli are comparable to those isolated from Lactobacillus 30a. At pH 4.8 the Km of wild-type enzyme is 0.4 mM and the kcat = 2800 min-1; the corresponding values for G58D are 0.5 mM and 2750 min-1. The wild-type and G58D have autoactivation half-times of 21 and 9 h respectively under pseudophysiological conditions of 150 mM K+ and pH 7.0. At pH 7.6 and 0.8 M K+ the half-times are 4.9 and 2.9 h. The relatively slow rate of autoactivation for purified protein and the differences in cellular and non-cellular activation rates, coupled with the fact that wild-type protein is readily activated in wild-type Lactobacillus 30a but poorly activated in E. coli, suggest that wild-type Lactobacillus 30a contains a factor, possibly an enzyme, that enhances the activation rate.

Carboxy-Lyases↗