Relationship between UDP-glucose 4-epimerase activity and oligoglucose glycoforms in two strains of Neisseria meningitidis

Sodium dodecyl sulfate-polyacrylamide gel analysis of lipooligosaccharide ( LOS) from Neisseria meningitidis has demonstrated considerable microheterog eneity in the variable region of LOS due to the presence of novel glycoform s, As a step toward understanding the basis for the expression of these nov el glycoforms, we have examined the LOS structures and UDP-glucose 4-epimer ase (epimerase) activity levels in two strains (NMB and MA-1) and their res pective galE mutants. Strain NMB was found to have low epimerase activity a nd to contain multiple glycoforms, some of which appear to contain only glu cose sugars. The galE mutant had only the oligoglucose glycoforms, Strain M A-1 had higher epimerase activity at both log and stationary phases (2- and 12.5-fold, respectively) and one glycoform with a putative lactosyl struct ure. Strain MA-1 galE had two glycoforms that contained one or two glucose residues. To understand I:he molecular basis for the different epimerase ac tivities, we examined the predicted amino acid sequences of the respective galE open reading frames and determined the relative amounts of GalE protei n. We found no significant differences between the predicted amino acid seq uence of the GalE protein in NMB and that in MA-1, We observed no significa nt differences in the level of GalE protein between MA-1 and NMB at exponen tial or stationary phase. We also observed an 8.2-fold drop in epimerase ac tivity in NMB between the log and stationary phases that was not due to the GalE protein level or low glucose levels.