1.B.72 The Protochlamydial Outer Membrane Porin (PomS/T) Family

The amoeba symbiont, Protochlamydia amoebophila, lacks a homologue of the most abundant outer membrane protein porin of the Chlamydiaceae, the major outer membrane protein MOMP, highlighting a major difference between environmental chlamydiae and their pathogenic counterparts. Aistleitner et al. 2013 identified a novel family of outer membrane proteins encoded in the genome of P. amoebophila by in silico analysis. Two of these Protochlamydial outer membrane proteins, PomS (pc1489) and PomT (pc1077), are highly abundant in outer membrane preparations of this organism. They are toxic when expressed in Escherichia coli. Immunofluorescence analysis using antibodies against heterologously expressed PomT and PomS purified directly from elementary bodies demonstrated that both proteins are in the outer membrane of P. amoebophila. The pomS gene is transcribed, and the encoded protein is present in the outer membrane throughout the complete developmental cycle, suggesting an essential role. Lipid bilayer measurements demonstrated that PomS functions as a porin with anion-selectivity and a pore size similar to that of Chlamydiaceae MOMP. Thus, PomS, possibly in concert with PomT and other members of this porin family n P. amoebophila, is the functional equivalent of MOMP (Aistleitner et al. 2013).