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1.B.52 The Oms28 Porin (Oms28P) Family

Skare et al. (1996) described porin activity with single-channel conductances of 0.6 nS in 1 M KCI. Oms28 is a 257-amino-acid precursor protein with a putative 24-amino-acid leader peptidase I signal sequence. Processed Oms28 yielded a mature protein with a predicted molecular mass of 25,363 Da. When overproduced in Escherichia coli, the Oms28 porin fractionated in the outer membrane. Sodium dodecyl sulfate-polyacrylamide gel-purified recombinant Oms28 from E. coli retained functional activity as demonstrated by an average single-channel conductance of 1.1 nS in the planar lipid bilayer assay, confirming that Oms28 is a B. burgdorferi porin (Skare et al., 1996).  The porin function of Oms28 (Bba74) has been questioned (Mulay et al. 2007).  Regulation of its synthesis has been studied (Mulay et al. 2009).  Much of the Oms28 sequence shows similarity with C-terminal regions of methylated chemotaxis proteins of bacteria. 

The generalized reaction proposed to be catalyzed by Oms28 is:

small molecules (out) small moleules (in)

References associated with 1.B.52 family:

Mulay, V., M.J. Caimano, D. Liveris, D.C. Desrosiers, J.D. Radolf, and I. Schwartz. (2007). Borrelia burgdorferi BBA74, a periplasmic protein associated with the outer membrane, lacks porin-like properties. J. Bacteriol. 189: 2063-2068. 17189354
Mulay, V.B., M.J. Caimano, R. Iyer, S. Dunham-Ems, D. Liveris, M.M. Petzke, I. Schwartz, and J.D. Radolf. (2009). Borrelia burgdorferi bba74 is expressed exclusively during tick feeding and is regulated by both arthropod- and mammalian host-specific signals. J. Bacteriol. 191: 2783-2794. 19218390
Skare, J.T., C.I. Champion, T.A. Mirzabekov, E.S. Shang, D.R. Blanco, H. Erdjument-Bromage, P. Tempst, B.L. Kagan, J.N. Miller, and M.A. Lovett. (1996). Porin activity of the native and recombinant outer membrane protein Oms28 of Borrelia burgdorferi. J. Bacteriol. 178: 4909-4918. 8759855