Porin

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

• Mycobacterium tuberculosis ArfA Rv0899 for OmpA type
  
• Osmoporin OmpC (E. coli)
  
• OmpF
  
• Molecular Playground/OmpG
  
• Molecular Playground/OmpG2
  
• Osmoporin OmpK36 (K. pneumoniae)
  

Structure

One representative porin structure is the crystal structure osmoporin OmpC from Escherichia coli (2j1n). OmpC has three beta-barrels associated to form a ^[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 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 with pseudoatoms. In an alternative visualization, channels are shown as , 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. The channels appear narrower in this animation than in the interactive scene because the animation shows the solvent accessible surface while the interactive view shows the molecular surface.

3D structures of Porin

Porin 3D structures