Function
Porin or Outer Membrane Proteins (Omps) act as channels which allow passive diffusion of sugars, ions and amino acids. They are beta barrel proteins which traverse the cell membrane. In E. coli they are named according to their genes: C, F, G, etc. (OmpC, OmpF, OmpG).
Voltage-Dependent Anion Channel (VDAC) are ion channel Omps found in outer mitochondrial membrane[1]. In Pseudomonas aeruginosa the porin gene products are named OprD, OprE, OprK, OprP, etc. and OpdC, OpdH, etc.
Maltoporin (LamB) facilitates the diffusion of maltodextrin across the membrane[2].
Chitoporin (Chitp) facilitates the diffusion of chitooligosaccharides across the outer membrane of some bacteria[3].
See more details in
Structure
One representative porin structure is the crystal structure osmoporin OmpC from Escherichia coli (2j1n). OmpC has three beta-barrels associated to form a tight trimer [4]. Porin is a transmembrane protein, as can be seen from the around the protein, this makes it possible to submerge in the lipid bilayer (hydrophobic amino acids are sandybrown, hydrophilic ones are cyan). As you can see the channel in the protein is made of mainly hydrophilic chains thus making it possible for the sugar to pass through (these scenes were created by Nádori Gergely).
The channels have wide openings on either side with a tighter bottleneck in the middle, as illustrated in the interactive view visualizing channels with pseudoatoms. In an alternative visualization, channels are shown as surfaces, slabbed on both sides of the bottleneck for better visibility.
Finally, the animation below shows a view perpendicular to the membrane, slicing through different layers of the porin structure with the solvent accessible surface shown in tan.
3D structures of Porin
Porin 3D structures
- ↑ Shoshan-Barmatz V, Israelson A, Brdiczka D, Sheu SS. The voltage-dependent anion channel (VDAC): function in intracellular signalling, cell life and cell death. Curr Pharm Des. 2006;12(18):2249-70. PMID:16787253
- ↑ Van Gelder P, Dumas F, Bartoldus I, Saint N, Prilipov A, Winterhalter M, Wang Y, Philippsen A, Rosenbusch JP, Schirmer T. Sugar transport through maltoporin of Escherichia coli: role of the greasy slide. J Bacteriol. 2002 Jun;184(11):2994-9. PMID:12003940
- ↑ Suginta W, Chumjan W, Mahendran KR, Schulte A, Winterhalter M. Chitoporin from Vibrio harveyi, a channel with exceptional sugar specificity. J Biol Chem. 2013 Apr 19;288(16):11038-46. PMID:23447539 doi:10.1074/jbc.M113.454108
- ↑ Basle A, Rummel G, Storici P, Rosenbusch JP, Schirmer T. Crystal structure of osmoporin OmpC from E. coli at 2.0 A. J Mol Biol. 2006 Oct 6;362(5):933-42. Epub 2006 Aug 3. PMID:16949612 doi:10.1016/j.jmb.2006.08.002
