Evaluation of temperature gradient capillary electrophoresis for detection of the Factor V Leiden mutation: coincident identification of a novel polymorphism in Factor V.

AIM: The Factor V Leiden mutation (G1691A) is a clinically important polymorphism that results in an increased risk of thrombosis. The goal of this study was to compare a temperature gradient capillary electrophoresis (TGCE) platform for the detection of Factor V gene mutations to a conventional restriction fragment length polymorphism (RFLP) assay. METHODS: Three hundred and four samples were analyzed by both TGCE and a common clinical Mnl I/RFLP assay. Concordance of results between the two assays was observed for 302/304 (99.3%) of the samples. RESULTS: All of the Leiden mutants (23/23, 100%) were identified by TGCE. Of the two discrepant results, one was caused by low peak heights in the TGCE output data and was easily rectified by the addition of a minimum peak height threshold. The second discrepancy resulted from the presence of a G-->A transition 95 bp downstream of the Leiden mutation site. This polymorphism represents a previously unreported alteration of the Factor V gene. CONCLUSIONS: The TGCE assay is less labor-intensive and has a higher throughput capacity than the Mnl I/RFLP assay. TGCE is a less specific assay than the Mnl I/RFLP assay that allows for the detection of novel polymorphisms, but also creates the need for all positive TGCE results to be confirmed by an alternate method such as sequencing. Our results demonstrate that TGCE is a highly sensitive method for mutation detection and has utility for mutation discovery analysis.

Biochemical characterization of a beta-galactosidase with a low temperature optimum obtained from an Antarctic arthrobacter isolate.

A psychrophilic gram-positive isolate was obtained from Antarctic Dry Valley soil. It utilized lactose, had a rod-coccus cycle, and contained lysine as the diamino acid in its cell wall. Consistent with these physiological traits, the 16S ribosomal DNA sequence showed that it was phylogenetically related to other Arthrobacter species. A gene (bgaS) encoding a family 2 beta-galactosidase was cloned from this organism into an Escherichia coli host. Preliminary results showed that the enzyme was cold active (optimal activity at 18 degrees C and 50% activity remaining at 0 degrees C) and heat labile (inactivated within 10 min at 37 degrees C). To enable rapid purification, vectors were constructed adding histidine residues to the BgaS enzyme and its E. coli LacZ counterpart, which was purified for comparison. The His tag additions reduced the specific activities of both beta-galactosidases but did not alter the other characteristics of the enzymes. Kinetic studies using o-nitrophenyl-beta-D-galactopyranoside showed that BgaS with and without a His tag had greater catalytic activity at and below 20 degrees C than the comparable LacZ beta-galactosidases. The BgaS heat lability was investigated by ultracentrifugation, where the active enzyme was a homotetramer at 4 degrees C but dissociated into inactive monomers at 25 degrees C. Comparisons of family 2 beta-galactosidase amino acid compositions and modeling studies with the LacZ structure did not mimic suggested trends for conferring enzyme flexibility at low temperatures, consistent with the changes affecting thermal adaptation being localized and subtle. Mutation studies of the BgaS enzyme should aid our understanding of such specific, localized changes affecting enzyme thermal properties.