Isolation of flagellated membrane vesicles from Caulobacter crescentus cells: evidence for functional differentiation of polar membrane domains.

An immunoaffinity chromatography procedure is described for the separation of membrane vesicles from Caulobacter crescentus cells into flagellated (polar) vesicles and nonflagellated (nonpolar) vesicles. Analysis by two-dimensional gel electrophoresis shows that a number of proteins are associated primarily with either the polar or the nonpolar fraction, and this result suggests that the envelope of these cells is organized into at least two relatively stable domains. Radioimmunoassay also shows that the membrane pool of flagellin, which is known to behave as a precursor in the assembly of the flagellar filament, may be localized exclusively in the polar membrane domain. Thus, the results provide biochemical evidence for the structural and functional differentiation of the C. crescentus cell envelope. These findings are consistent with a model we proposed previously to explain the targeting of surface structures to the new cell pole of C. crescentus. The immunoadsorption approach described here should be useful in the further investigation of this problem, as well as in the fractionation of membrane domains with characteristic surface antigens in other systems.