Burkholderia (formerly Pseudomonas) cepacia porin is an oligomer composed of two component proteins

Abstract

The 81 kDa protein (designated OpcPO) which forms a diffusion pore in the outer membrane of Burkholderia (formerly Pseudomonas) cepacia has a unique characteristic in that when the purified protein is heated it yields a major 36 kDa protein (designated OpcP1) and a minor 27 kDa protein (designated OpcP2). Moreover, incubation of OpcPO in citrate buffer at pH 3.0 produced an unusual dissociation into 72 kDa and 27 kDa proteins. For the characterization of OpcPO and its derivatives, OpcP1 and OpcP2 from purified OpcPO were isolated by preparative SDS-PAGE. Reconstitution of OpcPO using purified preparations of OpcP1 and OpcP2 indicated that these derivatives were not proteolytic fragments of OpcPO. Moreover, immunoblot assays with murine polyclonal antisera specific for OpcP1 and OpcP2 yielded the following results: (i) OpcP1 and OpcP2 are immunologically distinguishable proteins; (ii) the unusual dissociation of OpcPO in citrate buffer at pH 3.0 resulted in the release of OpcP2 from OpcPO, and the resulting 72 kDa protein was probably an oligomer of OpcP1; (iii) purified OpcP1 itself produced two additional 53 kDa and 72 kDa proteins spontaneously following elution from the bottom of the SDS-PAGE gel. From these findings, it was concluded that OpcPO is formed by the non-covalent association of OpcP2 with an oligomer of OpcP1 that has the ability to self-assemble.