1.B.58 The Nocardial Hetero-oligomeric Cell Wall Channel (NfpA/B) Family

The cell wall outer membrane of Nocardia farcinica contains a cation-selective cell wall channel, which may be responsible for the limited permeability of the cell wall of N. farcinica to negatively charged antibiotics. Based on partial sequencing of the protein responsible for channel formation derived from N. farcinica ATTC 3318, Klackta et al. (2010) were able to identify the corresponding genes (nfa15890 and nfa15900) within the known genome of N. farcinica IFM 10152. The corresponding genes of N. farcinica ATTC 3318 were separately expressed in Escherichia coli and purified to homogeneity. The proteins were designated NfpA and NfpB, for N. farcinica porin A and B. The proteins together (but not alone) could form channels in lipid bilayer membranes.

The generalized reactin catalyzed by the NfpA/NfpB complex is:

small molecules (out) %u21CC small molecules (in).

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



Klackta C., Knorzer P., Riess F. and Benz R. (2011). Hetero-oligomeric cell wall channels (porins) of Nocardia farcinica. Biochim Biophys Acta. 1808(6):1601-10.

Nishida, S., Y. Morinaga, H. Obata, and T. Mizuno. (2011). Identification of the N-terminal region of TjZNT2, a Zrt/Irt-like protein family metal transporter, as a novel functional region involved in metal ion selectivity. FEBS J. 278: 851-858.

Parkin, J. and S. Khalid. (2014). Atomistic molecular-dynamics simulations enable prediction of the arginine permeation pathway through OccD1/OprD from Pseudomonas aeruginosa. Biophys. J. 107: 1853-1861.

Singh, P.R., H. Bajaj, R. Benz, M. Winterhalter, and K.R. Mahendran. (2015). Transport across the outer membrane porin of mycolic acid containing actinomycetales: Nocardia farcinica. Biochim. Biophys. Acta. 1848: 654-661.


TC#NameOrganismal TypeExample

The heteromeric porin, NfpA/NfpB (Kläckta et al., 2010). Sugars, amino acids and antibiotics are transported. The cation selective N. farcinica channel exhibits strong interactions with the positively charged antibiotics; amikacin and kanamycin, and the negatively charged ertapenem (Singh et al. 2015).


NfpA/NfpB of Nocardia farcinica
NfpA (234aas) (Q5YZF6)
NfpB (229aas) (Q5YZF5)


MspA porin homologue (200aas; 1 N-terminal TMS)


MspA porin of Nocardia brasiliensis (H5RPX4)


MspA family member (263aas; 1 N-terminal TMS)


MspA porin of Segniliparus rotundus (D6Z9R0)


MspA porin homologue (212 aas; 1 N-terminal TMS)


MspA porin of Mycobacterium abscessus


Putative porin


Porin of Rhodococcus erythropolis


Putative porin of 222 aas.


MspA homologue of Gordonia soli


Putative porin, MspA of 221 aas.


MspA of Gordonia bronchialis