Molecular structure of membrane vesicles from Escherichia coli

Abstract

The molecular architecture of membrane vesicles prepared from Escherichia coli ML 308-225 has been studied by using crossed immunoelectrophoresis, and a reference pattern of 52 discrete immunoprecipitates has been established. Progressive immunoadsorption experiments conducted with untreated control vesicles and with physically disrupted vesicles demonstrate that the membrane-associated immunogens fall into two categories: (i) those immunogens typified by ATPase (ATP phosphohydrolase, EC 3.6.1.3) and NADH dehydrogenase [NADH: (acceptor) oxidoreductase, EC 1.6.99.3] whose expression is minimal unless the vesicles are disrupted; and (ii) immunogens such as Braun's lipoprotein that are expressed to similar extents in untreated and in disrupted vesicles. A mathematical relationship between the peak area subtended by an immunoprecipitate in the crossed immuno-electrophoresis system and the quantity of vesicles used in the adsorption process has been derived. This relationship allows quantitation of the degree to which specific membrane immunogens partition between exposed and unexposed surfaces of the vesicle membrane. The results demonstrate conclusively that >95% of the membrane in the vesicle preparations is in the form of sealed sacculi with the same polarity as the intact cell. Moreover, the findings provide a strong indication that dislocation of immunogens from the inner to the outer surface of the membrane during vesicle preparation does not occur to an extent exceeding 11%.