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).
Outer membrane porin, PomS of 317 aas (Aistleitner et al. 2013).
PomS of Protochlamydia amoebophila
Outer membrane porin, PomT of 345 aas (Aistleitner et al. 2013).
PomT of Protochlamydia amoebophila
Putative porin of 366 aas
PP of Accumulibacter phosphatis
Putative porin of 300 aas
PP of Pedobacter saltans
Uncharacterized protein of 308 aas
UP of Chitinophaga pinensis
Uncharacterized protein of 325 aas
UP of Protochlamydia amoebophila
Uncharacterized protein of 343 aas. This sequence is homologous to the C-terminal 300 aas of 1.B.72.2.2, 2.3 and 2.4.
UP of Candidatus Nitrospira defluvii
Uncharacterized protein of 487 aas. This protein has an N-terminal 200 aas that are proline rich, and a C-terminal region homologous to 1.B.72.2.1, 2.3 and 2.4. Shows a region of 90 aas that is 31% identical to 1.B.72.1.3.
UP of Rhodovulum sp. PH10
Uncharacterized protein of 577 aas. This protein has an N-terminal 250 aas that are homologous to 1.B.4.2.1 and other members of the BRP family, but a C-terminal 300 aas that are homologous to the other members of subfamily 2 of the PomS/T family (1.B.72).
UP of Hyphomicrobium nitrativorans
Uncharacterized protein of 1086 aas. Only the C-terminal 300 aas show sequence similiarity with other members of subfamily 1.B.72.2. Residues 235 - 291 show 35% identity (e-5)with YgbF of E. coli (2.C.1.2.1).
UP of Bradyrhizobium oligotrophicum
Uncharacterized protein of 315 aas.
UP of Pelagibacterium halotolerans