1.B.92. The Proteobacterial Outer Membrane Porin, NilB (NilB), Family The γ-proteobacterium Xenorhabdus nematophila is a mutualistic symbiont that colonizes the intestine of the nematode Steinernema carpocapsae. NilB (nematode intestine localization) is essential for X. nematophila colonization of nematodes and is predicted to encode an integral outer membrane beta-barrel protein. When expressed with two other factors encoded by nilA and nilC, it confers upon non-cognate Xenorhabdus spp. the ability to colonize S. carpocapsae nematodes. Bhasin et al. 2012 presented evidence that NilB is a surface-exposed outer membrane β-barrel protein whose expression is repressed by NilR when grown in nutrient rich medium. Bioinformatic analyses reveal that NilB is the only functionally characterized member of a family of proteins distinguished by N-terminal region tetratricopeptide repeats (TPR) and a conserved C-terminal domain of unknown function (DUF560). Members of this family occur in diverse bacteria, and are prevalent in the genomes of mucosal pathogens. Insertion and deletion mutational analyses support a beta-barrel structural model with an N-terminal globular domain, fourteen transmembrane strands, and seven extracellular surface loops. The globular domain and surface loop 6 play a role in nematode colonization. NilB is necessary at early stages of colonization (Bhasin et al. 2012).
This family belongs to the Outer Membrane Pore-forming Protein I (OMPP-I) Superfamily .
References:
Bhasin, A., J.M. Chaston, and H. Goodrich-Blair. (2012). Mutational analyses reveal overall topology and functional regions of NilB, a bacterial outer membrane protein required for host association in a model of animal-microbe mutualism. J. Bacteriol. 194: 1763-1776.
Examples:
TC#	Name	Organismal Type	Example
1.B.92.1.1	*NilB; 14 β-TMS outer membrane porin of 466 aas (Bhasin et al., 2012).*	Gram-negative bacteria	*NilB of Xenorhabdus nematophila* (Q8RLV4)**

1.B.92.1.2	OmpU	Gram-negative bacteria	*OmpU of Neisseria meningitidis* (Q5F674)**

1.B.92.1.3	Outer membrane protein, OMP	Gram-negative bacteria	*OMP of Mannheimia haemolytica* (E2PBK0)**

1.B.92.1.4	Outer membrane protein, OMP	Gram-negative bacteria	*OMP of Taylorella equigenitalia* (E8UCW3)**

1.B.92.1.5	Putative porin of 415 aas	Proteobacteria	Putative porin of Bibersteinia trehalosi

1.B.92.1.6	Uncharacterized DUF560 domain-containing protein of442 aas.		UP of Aestuariibacter salexigens

1.B.92.1.7	Uncharacterized protein of 456 aas and 1 N-terminal TMS.		UP of Arsenophonus nasoniae

Examples:
TC#	Name	Organismal Type	Example
1.B.92.2.1	Uncharacterized DUF560 domain-containing proteinof384 aa		UP of Amylibacter cionae

1.B.92.2.2	Uncharacterized DUF560 domain-containing protein of 436 aas and 1 N-terminal TMS.		UP of Martelella mediterranea

1.B.92.2.3	Putative porin of 471 aas and 1 N-terminal TMS.		*Porin of Candidatus Synechococcus spongiarum* 142**

1.B.92.2.4	Surface lipoprotein assembly modifier of 444 aas with 1 N-terminal TMS and possibly 2 additional TMSs.		LAM of Emcibacter nanhaiensis