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1.B.2 The Chlamydial Porin (CP) Family

The chlamydial major outer membrane porin, MomP, OmpA, Omp1L2, or Omp1, functions to permit the diffusion of solutes through the intrareticular body membrane. It has ~402 amino acyl residues and is believed to be disulfide-bonded to two other outer membrane constituents, OmcA, a lipid-anchored 9 kDa protein with ~ 14 cys residues, and OmcB, a 60 kDa protein with ~37 cys (Findlay et al. 2005). A homologue, PorB, which transports neutral solutes poorly, has been shown to transport dicarboxylates such as 2-ketoglutarate (Kubo and Stephens, 2001).

MOMP trimers are stable under reducing conditions, although disulfide bonds appear to be present between the monomers of a trimer and between trimers (Sun et al., 2007). Cross-linking of the Chlamydial outer membrane complex (COMC) demonstrated that the MOMP is probably disulfide-linked and in a close spatial relationship with the 60- and 12-kDa cysteine-rich proteins, OmcB and OmcA, respectively. The trimers consist mainly of β-pleated sheet structures. Using a liposomal swelling assay, the MOMP was found to have porin activity, approximately 2 nm in diameter (Sun et al., 2007). 

References associated with 1.B.2 family:

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Findlay, H.E., H. McClafferty, and R.H. Ashley. (2005). Surface expression, single-channel analysis and membrane topology of recombinant Chlamydia trachomatis Major Outer Membrane Protein. BMC Microbiol 5: 5. 15673471
Jeanteur, D., J.H. Lakey, and F. Pattus. (1991). The bacterial porin superfamily: sequence alignment and structure prediction. Mol. Microbiol. 5: 2153-2164. 1662760
Jeanteur, D., J.H. Lakey, and F. Pattus. (1994). The porin superfamily: diversity and common features. In: Bacterial Cell Wall. Edited by Ghuysen, J.M., Hakenbeck, R. Elsevier, Amsterdam, pp. 363-380.
Kubo, A. and R.S. Stephens. (2000). Characterization and functional analysis of PorB, a Chlamydia porin and neutralizing target. Mol. Microbiol. 38: 772-780. 11115112
Kubo, A. and R.S. Stephens. (2001). Substrate-specific diffusion of select dicarboxylates through Chlamydia trachomatis PorB. Microbiology 147: 3135-3140. 11700364
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Pickett, M.A., M.E. Ward, and I.N. Clarke. (1988b). High-level expression and epitope localization of the major outer membrane protein of Chlamydia trachomatis serovar L1. Mol. Microbiol. 2: 681-685. 2460720
Pickett, M.A., S.J. Everson, and I.N. Clarke. (1988a). Chlamydia psittaci ewe abortion agent: complete nucleotide sequence of the major outer membrane protein gene. FEMS Microbiol. Lett. 55: 229-234.
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Sadhasivam, A., H. Nagarajan, and V. Umashankar. (2019). Structure-based drug target prioritisation and rational drug design for targeting eye infections. J Biomol Struct Dyn 1-13. [Epub: Ahead of Print] 31380730
Schulz, G.E. (1996). Porins: general to specific, native to engineered passive pores. Curr. Opin. Struc. Biol. 6: 485-490. 8794162
Sun, G., S. Pal, A.K. Sarcon, S. Kim, E. Sugawara, H. Nikaido, M.J. Cocco, E.M. Peterson, and L.M. de la Maza. (2007). Structural and Functional Analyses of the Major Outer Membrane Protein of Chlamydia trachomatis. J. Bacteriol. 189:6222-6235. 17601785