Biomedical subjects

Maciej Lis

Publications and source records attributed to Maciej Lis.

3 recordsLinked to original sources

PubMed2005

A modified, dual reporter TOXCAT system for monitoring homodimerization of transmembrane segments of proteins.

The TOXCAT assay system developed by Russ and Engelman [TOXCAT: a measure of transmembrane helix association in a biological membrane, Proc. Natl. Acad. Sci. USA 96 (1999) 863-868] provides an in vivo means of selecting for and evaluating the strength of interaction between identical transmembrane alpha-helices. In the course of utilizing TOXCAT to study the architecture of a sodium channel hNa(V)1.5, an apparently strong dimerization of two of its putative transmembrane segments was revealed. Following random mutagenesis of these regions, several amino acids critical for the observed dimerizations were identified. In order to develop a more efficient means of isolating mutations which specifically disrupt dimerization of these transmembrane segments without affecting their membrane-targeting properties, we developed a modification to the original TOXCAT design in which the C-terminal maltose binding protein moiety is replaced by the beta-lactamase. We show that this assay system is capable of simultaneously monitoring the integrity of the chimeric protein, its membrane insertion activity, and the ability of the transmembrane segment under study to dimerize.

Amino Acid Sequence↗

PubMed2003

Characterization of a suppressor mutation complementing an acid-sensitive mutation in Streptococcus mutans.

We isolated a spontaneous suppressor mutant complementing the acid-sensitive phenotype of Streptococcus mutans strain Tn-1, a mutant previously generated in this laboratory, defective in the activity of the dgk-encoded putative undecaprenol kinase. A relatively simple genetic method was developed to identify the suppressor mutation, based on selection for transformants containing two closely linked markers: a selectable allele of the unknown suppressor gene and an antibiotic resistance gene introduced on a suicide plasmid at random sites into the chromosome via homologous recombination. While we have not actually identified the original suppressor mutation, another mutated gene restoring acid resistance has been isolated, which suggests a possible mechanism of suppression.

Acids↗

PubMed2003

The stress-responsive dgk gene from Streptococcus mutans encodes a putative undecaprenol kinase activity.

We analyzed a previously constructed stress-sensitive Streptococcus mutans mutant Tn-1 strain resulting from disruption by transposon Tn916 of a gene encoding a protein exhibiting amino acid sequence similarity to the Escherichia coli diacylglycerol kinase. It was confirmed that the mutation led to significantly reduced lipid kinase activity, while expression of the intact gene on a plasmid restored both kinase activity and the wild-type phenotype. Further analysis revealed that the product of the dgk gene in S. mutans predominantly recognizes a lipid substrate other than diacylglycerol, most likely undecaprenol, as demonstrated by its efficient phosphorylation and the resistance of the product of the reaction to saponification. The physiological role of the product of the dgk gene as a putative undecaprenol kinase was further supported by a significantly higher sensitivity of the mutant to bacitracin compared with that of the parental strain.

Bacterial Proteins↗