This gene codes for the cyclic (3 (1-2) glucan synthetase (cgs), an integral inner membrane protein of 2831 amino acids with 51% identity to S. meliloti NdvB. In S. meliloti, ndvB is required for effective invasion of the nodules and in A. tumefaciens chvB is involved in tumor induction. B. abortus cgs mutants have reduced virulence in mice and defective intracellular multiplication in HeLa cells.
B. abortus cgs expressed under its own promoter complemented S. meliloti ndvB and A. tumefaciens chvB mutants. Studies on the interaction between B. abortus cgs mutants with mammalian cells, revealed that cyclic p (1-2) glucan is not required for cell invasion. However, the ability to prevent fusion between early endosomes with lysosomes is severely reduced. A small number of cyclic p (1-2) glucan minus mutant cells reach the endoplasmic reticulum to establish their intracellular multiplication niche, explaining their reduced virulence. The addition of purified p (1-2) glucan during cell infection partly restored the wild-type phenotype.
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