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).
This family belongs to the Outer Membrane Pore-forming Protein I (OMPP-I) Superfamily .
References:
Aistleitner, K., C. Heinz, A. Hörmann, E. Heinz, J. Montanaro, F. Schulz, E. Maier, P. Pichler, R. Benz, and M. Horn. (2013). Identification and characterization of a novel porin family highlights a major difference in the outer membrane of chlamydial symbionts and pathogens. PLoS One 8: e55010.
Examples:
TC#	Name	Organismal Type	Example
1.B.72.1.1	*Outer membrane porin, PomS of 317 aas (Aistleitner et al.* 2013).**	Chlamydiae	PomS of Protochlamydia amoebophila

1.B.72.1.2	*Outer membrane porin, PomT of 345 aas (Aistleitner et al.* 2013).**	Chlamydiae	PomT of Protochlamydia amoebophila

1.B.72.1.3	Putative porin of 366 aas	Proteobacteria	PP of Accumulibacter phosphatis

1.B.72.1.4	Putative porin of 300 aas	Bacteroidetes	PP of Pedobacter saltans

1.B.72.1.5	Uncharacterized protein of 308 aas	Bacteroidetes	UP of Chitinophaga pinensis

1.B.72.1.6	Uncharacterized protein of 325 aas	Chlamydiae	UP of Protochlamydia amoebophila

Examples:
TC#	Name	Organismal Type	Example
1.B.72.2.1	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.	Nitrospirae	UP of Candidatus Nitrospira defluvii

1.B.72.2.2	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.	Proteobacteria	*UP of Rhodovulum* sp. PH10**

1.B.72.2.3	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).	Proteobacteria	UP of Hyphomicrobium nitrativorans

1.B.72.2.4	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).	Proteobacteria	UP of Bradyrhizobium oligotrophicum

1.B.72.2.5	Uncharacterized protein of 315 aas.	Proteobacteria	UP of Pelagibacterium halotolerans

Examples:
TC#	Name	Organismal Type	Example
Examples:
TC#	Name	Organismal Type	Example