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).