1.B.163.  The Cell Wall (Outer Membrane) Porin-2 (PorA2) Family

This family (DUF3068; pfam11271) includes members of about 375 aas with two very hydrophobic TMSs at the N- and C-termini.  The PorA of Corynebacterium amycolatum forms water-filled channels that favor the permeation of cations (Dörner et al. 2009, Soltan Mohammadi et al. 2013). The cell-wall channel is wide and water-filled and has a narrow selectivity for cations (Dörner et al. 2009).



Dörner, U., B. Schiffler, M.A. Lanéelle, M. Daffé, and R. Benz. (2009). Identification of a cell-wall channel in the corynemycolic acid-free Gram-positive bacterium Corynebacterium amycolatum. Int Microbiol 12: 29-38.

Gupta, K.R., C.M. Gwin, K.C. Rahlwes, K.J. Biegas, C. Wang, J.H. Park, J. Liu, B.M. Swarts, Y.S. Morita, and E.H. Rego. (2022). An essential periplasmic protein coordinates lipid trafficking and is required for asymmetric polar growth in mycobacteria. Elife 11:. [Epub: Ahead of Print]

Piselli, C., L. Benier, C. Koy, M.O. Glocker, and R. Benz. (2022). Cell wall channels of Rhodococcus species: identification and characterization of the cell wall channels of Rhodococcus corynebacteroides and Rhodococcus ruber. Eur Biophys. J. [Epub: Ahead of Print]

Soltan Mohammadi, N., S. Mafakheri, N. Abdali, I. Bárcena-Uribarri, A. Tauch, and R. Benz. (2013). Identification and characterization of the channel-forming protein in the cell wall of Corynebacterium amycolatum. Biochim. Biophys. Acta. 1828: 2574-2582.


TC#NameOrganismal TypeExample

Mycolic acid outer membrane porin, PorA(2) of 374 aas and 2 hydrophobic peaks at its N- and C-termini.  The protein forms pores that are slightly cation-selective.

PorA of Corynebacterium amycolatum


DUF3068 PorA porin of 364 aas and two TMSs, N- and C-terminal.

PorA of Corynebacterium diphtheriae


DUF3068 domain-containing protein, PorA, of 331 aas and 2 N- and C-terminal TMSs.

PorA(2) of Streptomyces inusitatus


PorA of 340 aas and 2 TMSs.

PorA of Actinoallomurus bryophytorum


DUF3068 domain-containing protein, PorA(2) of 359 aas with 2 TMSs.

PorA(2) of Nocardiopsis potens


Porin PorA family protein of 363 aas and 2 TMSs. 

PorA of Catenulispora pinistramenti


DUF3068 domain-containing protein of 321 aas and 2 TM

DUF3068 domain protein of Nonomuraea glycinis


PorA of 391 aas and 2 TMSs, N- and C-terminal (Piselli et al. 2022).

PorA of Rhodococcus ruber


PgfA (MSMEG_0317), a periplasmic protein, interacts with trehalose monomycolate (TMM) and MmpL3 (TC# 2.A.6.5.6).   It is a key determinant of polar growth and cell envelope composition in mycobacteria, and the LamA-mediated recruitment of this protein to one side of the cell is a required step in the establishment of cellular asymmetry (Gupta et al. 2022).

PgfA of Mycolicibacterium smegmatis (Mycobacterium smegmatis; mycobacterium phlei)