1.B.7 The Rhodobacter PorCa Porin (RPP) Family

The Rhodobacter PorCa Protein, the only well characterized member of the RPP family, was the first porin to yield its three-dimensional structure by X-ray crystallography. It has a 16-stranded β-barrel structure similar to that of the members of the GBP (TC #1.B.1) family. Paupit et al. (1991) presented crystal structures of phosphoporin (PhoE; TC# 1.B.1.1.2), maltoporin (1.B.3.1.1; LamB) and Matrixporin (OmpF), all of E. coli, and found these have 3-d folds similar to that of the Rhodobacter porin, PorCa. It was not determined if this similarity is due to divergent evolution from a common ancestor or covergent evolution from dissimilar precursors. However, we have been able to demonstrate homology between members of families 1.B.1 and 1.B.7 using statistical means (M. Saier, unpublished results).

This family belongs to the Outer Membrane Pore-forming Protein (OMPP) Superfamily I.



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TC#NameOrganismal TypeExample

PorCa (B10) porin.  The 3-d structure is known (PDB ID 2POR).

Bacteria PorCa porin of Rhodobacter capsulatus

Paracoccus ion non-selective porin with 16 putative beta-strands, PorG (Saxena et al. 1997).


Porin of Paracoccus denitrificans


PorI (OpmA) porin.  Forms channels that allow the passive diffusion of small hydrophilic solutes up to an exclusion limit of about 600 Da.  The 3-d structure is known (PDB ID 1PRN).


PorI porin of Rhodobacter (Rhodopseudomonas) blastica


OmaA major-porin (Burdman et al., 2000).

Gram-negative bacteria

OmaA of Azospirillum brasilense (Q9F9L3)


Porin 41 (Por41) (Kleeberg, V., Neumann, U., Schultz, G.E. and Weckesser, J., unpublished)

Gram-negative bacteria

Por41 of Rhodospirillum rubrum (Q9K556)

1.B.7.1.6Outer membrane porin


SPO3430 of Silicibacter pomeroyi

Putative porin of 332 aas


Putative porin of Rhodopseudomonas sphaeroides


Porin of 385 aas (Moumène et al. 2015).


Porin of Ehrlichia ruminantium


TC#NameOrganismal TypeExample