Porins of Brucella species.

The outer membrane of Brucella species contains two major proteins, denoted as group 2 and group 3 proteins (Verstreate et al., Infect. Immun. 35:979-989, 1982). We reconstituted proteoliposomes from the purified proteins and egg phosphatidylcholine and showed that group 2 proteins, but not a group 3 protein, had the porin activity. The influx rates of sugars of various sizes into the proteoliposomes indicated that the porin channels had apparent diameters in a range comparable to that of Escherichia coli OmpF porin and that the channels were predominantly open. Among different Brucella species, there were small but detectable differences in the channel diameter, and it was possible to explain the differential sensitivity of several Brucella species to diagnostic dyes on the basis of these observed differences.