1.B.56 The Spirochaete Outer Membrane Porin (S-OMP) Family
Relapsing fever is a worldwide, endemic disease caused by several spirochetal species belonging to the genus Borrelia. During the recurring fever peaks, Borreliae proliferate quickly compared to the slow dissemination of Lyme disease Borrelia and therefore require efficient nutrient uptake from the blood of their hosts. Thein et al. (2008) described the first relapsing fever porin, which is present in the outer membranes of B. duttonii, B. hermsii, B. recurrentis, and B. turicatae. The pore-forming protein was designated Oms38, for outer membrane-spanning protein of 38 kDa. Oms38 was inserted with black lipid bilayers demonstrating that Oms38 forms small, water-filled channels of 80 pS in 1 M KCl that did not exhibit voltage-dependent closure. The Oms38 channel is slightl selective for anions and shows a ratio of permeability for cations over anions of 0.41 in KCl. Analysis of the deduced amino acid sequences demonstrated that Oms38 contains an N-terminal signal sequence which is processed under in vivo conditions. Oms38 is highly conserved within the four studied relapsing fever species, sharing an overall amino acid identity of 58% and with a strong indication for the presence of amphiphatic β-sheets. Homologues are found in Treponema species and Fibrobacter succinogens.
The generalized transport reaction catalyzed by Oms38 is:
molecules (in)→molecules (out) with slight anion selectivity.