Purification and reconstitution of the methyl-accepting chemotaxis proteins from Bacillus subtilis

The methyl-accepting chemotaxis proteins (MCPs) from Bacillus subtilis, designated as H1, H2, and H3, have been purified to near homogeneity. These purified MCPs were reconstituted into proteoliposome vesicles using a detergent dilution procedure. The ability of the reconstituted MCPs to be methylated in vitro strongly suggests that they are in a functionally active conformation. The MCPs of B. subtilis are considerably larger than those of Escherichia coli, with molecular weights of the purified proteins being 76, 86, and 97 kDa for H3, H2, and H1, respectively. Two-dimensional electrophoresis demonstrates that the isoelectric point of H1 and H2 is 5.1, while H3 is slightly more basic, having an isoelectric point of 5.3. Immunoblot analysis using the cross reacting E. coli anti-Trg antibody reveals that maximal MCP expression occurs approx. 4 h after the onset of stationary phase, and remains relatively stable thereafter. However, the ability of the MCPs to be methylated in vivo is significantly reduced.