TCDB is operated by the Saier Lab Bioinformatics Group

1.B.27 The Helicobacter Outer Membrane Porin (Hop) Family

The Hop family consists of 31 outer membrane proteins in Helicobacter pylori. Five such proteins, HopA-HopE have been shown to function as porins both in bacterial outer membranes and in reconstituted planar bilayer membranes. The HopE protein appears to form a β-barrel with 16 transmembrane amphipathic β-strands. It is the smallest of the characterized Hop family members, but it forms the largest channels with a single channel conductance of 1.5 nS in 1M KCl (Bina et al. 2000). 

Helicobacter pylori attaches to gastric tissue through members of a paralogous family of 'Helicobacter outer membrane proteins' (Hops), including adhesins BabA, SabA, HopQ, LabA and HopZ. Hops share a conserved 25 kDa C-terminal region that is thought to form an autotransporter-like transmembrane domain. Hops contain a non-continuous transmembrane domain, composed of seven predicted beta-strands at the C-terminus and one at the N-terminus (Coppens et al. 2018). Folding and outer membrane localization of the C-terminal beta-domain depends on a predicted transmembrane beta-strand within the first 16 N-terminal residues. The N-terminus resides in the periplasm, and the crystal and small angle X-ray scattering structures for the SabA extracellular domain reveal a conserved coiled-coil stem domain that connects to transmembrane beta-strands 1 and 2. Thus, Hop adhesins represent a novel outer membrane protein topology encompassing an OmpA-like 8-stranded beta-barrel that is interrupted by a 15 - 108 kDa domain inserted inside the first extracellular loop. The insertion of large, folded domains in extracellular loops is unprecedented in bacterial outer membrane proteins (Coppens et al. 2018).  It is possible that these proteins are autotransporters.

The generalized transport reaction catalyzed by Hop family porins is:

solute (out) solute (periplasm)

References associated with 1.B.27 family:

Bina, J., M. Bains, and R.E. Hancock. (2000). Functional expression in Escherichia coli and membrane topology of porin HopE, a member of a large family of conserved proteins in Helicobacter pylori. J. Bacteriol. 182: 2370-2375. 10762234
Coppens, F., G. Castaldo, A. Debraekeleer, S. Subedi, K. Moonens, A. Lo, and H. Remaut. (2018). Hop-family Helicobacter outer membrane adhesins form a novel class of Type 5-like secretion proteins with an interrupted β-barrel domain. Mol. Microbiol. 110: 33-46. 29995350
de Jonge, R., R.G. Pot, R.J. Loffeld, A.H. van Vliet, E.J. Kuipers, and J.G. Kusters. (2004). The functional status of the Helicobacter pylori sabB adhesin gene as a putative marker for disease outcome. Helicobacter 9: 158-164. 15068418
Kennemann, L., B. Brenneke, S. Andres, L. Engstrand, T.F. Meyer, T. Aebischer, C. Josenhans, and S. Suerbaum. (2012). In vivo sequence variation in HopZ, a phase-variable outer membrane protein of Helicobacter pylori. Infect. Immun. 80: 4364-4373. 23027539
Lienlaf, M., J.P. Morales, M.I. Díaz, R. Díaz, E. Bruce, F. Siegel, G. León, P.R. Harris, and A. Venegas. (2010). Helicobacter pylori HopE and HopV porins present scarce expression among clinical isolates. World J Gastroenterol 16: 320-329. 20082477
Paraskevopoulou, V., V.G. Artiaga, R. Rowlinson, G.S. Winkler, P. Gellert, S. Stolnik, R. Overman, and F.H. Falcone. (2019). Introduction of a C-terminal hexa-lysine tag increases thermal stability of the LacDiNac binding adhesin (LabA) exodomain from Helicobacter pylori. Protein Expr Purif 163: 105446. 31271862
Peck, B., M. Ortkamp, K.D. Diehl, E. Hundt, and B. Knapp. (1999). Conservation, localization and expression of HopZ, a protein involved in adhesion of Helicobacter pylori. Nucleic Acids Res 27: 3325-3333. 10454640
Tomb, J.F., O. White, A.R. Kerlavage, R.A. Clayton, G.G. Sutton, R.D. Fleischmann, K.A. Ketchum, H.P. Klenk, S. Gill, B.A. Dougherty, K. Nelson, J. Quackenbush, L. Zhou, E.F. Kirkness, S. Peterson, B. Loftus, D. Richardson, R. Dodson, H.G. Khalak, A. Glodek, K. McKenney, L.M. Fitzegerald, N. Lee, M.D. Adams, E.K. Hickey, D.E. Berg, J.D. Gocayne, T.R. Utterback, J.D. Peterson, J.M. Kelley, M.D. Cotton, J.M. Weidman, C. Fujii, C. Bowman, L. Watthey, E. Wallin, W.S. Hayes, M. Borodovsky, P.D. Karp, H.O. Smith, C.M. Fraser, and J.C. Venter. (1997). The complete genome sequence of the gastric pathogen Helicobacter pylori. Nature 388: 539-547. 9252185