The Mycobacterium bovis BCG cyclic AMP receptor-like protein is a functional DNA binding protein in vitro and in vivo, but its activity differs from that of its M-tuberculosis ortholog, RV3676

Mycobacterium tuberculosis Rv3676 encodes a cyclic AMP (cAMP) receptor-like protein (CRPMt) that has been implicated in global gene regulation and may play an important role during tuberculosis infection. The CPPMt ortholog in Mycobacterium bovis BCG, CRPBCG, is dysfunctional in an Escherichia coli CRP competition assay and has been proposed as a potential source of M. bovis BCG's attenuation. We compared CRPBCG and CRPMt in vitro and in vivo, in M. bovis BCG and M. tuberculosis, to evaluate CRPBCG'S potential function in a mycobacterial system. Both proteins formed dimers; in mycobacterial lysates, bound to the same target DNA sequences, and were similarly affected by the presence of cAMP in DNA binding assays. However, CRPMt and CRPBCG differed in their relative affinities for specific DNA target sequences and in their susceptibilities to protease digestion. Surprisingly, CRPBCG DNA binding activity was stronger than that of CRPMt both in vitro and in vivo, as measured by electrophoretic mobility shift and chromatin immunoprecipitation assays. Nutrient starvation-associated regulation of several CRPMt regulon members also differed between M. bovis BCG and M. tuberculosis. We conclude that CRPBCG is a functional cAMP-responsive DNA binding protein with an in vivo DNA binding profile in M. bovis BCG similar to that of CRPMt in M. tuberculosis. However, biologically significant functional differences may exist between CRPBCG and CRPMt with respect to gene regulation, and this issue warrants further study.