View source for Porin

[[Image:Porin wobble.gif|right]][[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). While porins all share a common fold, the detailed makeup and the shape of the inside of the barrel (the channel) determines which molecules pass through the porin and which are retained. 

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== Function ==
The function on a porin depends on the size and lining of the channel. 
*'''OprB''' is a carbohydate-selective porin<ref>PMID:7768797</ref>.
*'''OprF''' protects ''Pseudomonas aeruginosa'' against macrophage clearance<ref>PMID:33432030</ref>.
*'''PorB''' protects ''Neisseria meningitidis'' against antibiotics<ref>PMID:24145542</ref>.
*'''Maltoporin''' (LamB) facilitates the diffusion of maltodextrin across the membrane<ref>PMID:12003940</ref>.

*'''Chitoporin''' (Chitp) facilitates the diffusion of chitooligosaccharides across the outer membrane of some bacteria<ref>PMID:23447539</ref>.

*'''Voltage-Dependent Anion Channel (VDAC)''' are ion channel Omps found in outer mitochondrial membrane<ref>PMID:16787253</ref>.  In ''Pseudomonas aeruginosa'' the porin gene products are named OprD, OprE, OprK, OprP, etc. and OpdC, OpdH, etc.

For discussion of specific porins, see<br />
*[[Mycobacterium tuberculosis ArfA Rv0899]] for OmpA type<br />
*[[Osmoporin OmpC (E. coli)]]<br />
*[[OmpF]]<br /> 
*[[Molecular Playground/OmpG]]<br />
*[[Molecular Playground/OmpG2]]<br />
*[[Osmoporin OmpK36 (K. pneumoniae)]]<br />  

== Structure ==
<StructureSection load='' size='450' side='right' scene='41/411405/Membrane/1' caption='E. coli OmpC is a trimeric transmembrane protein with a porin fold (PDB code [[2j1n]])'>
One representative porin structure is the crystal structure osmoporin OmpC from ''Escherichia coli'' ([[2j1n]]). OmpC has three beta-barrels associated to form a <scene name='Porin/Cv/2'>tight trimer</scene> <ref>PMID:16949612</ref>. 

Porin is a <scene name='41/411405/Membrane/1'>transmembrane protein</scene>, as can be seen from the <jmol><jmolLink><script>script "/scripts/1a0s/Hidrophobic/1.spt"; ppdiaCaptionCmd = "changeCaption('Hydrophobic residues (shown in tan) are prevalent where the protein comes in contact with the hydrophobic layer of the double-layer membrane, while other parts of the surface are hydrophilic (hydrophilic residues, ordered water molecules and calcium ions shown in skyblue). Shown here is the sucrose-specific porin (PDB-ID 1a0s) in its trimeric quaternary structure.','white','black');";javascript @ppdiaCaptionCmd;</script><text>hydrophobic ring</text></jmolLink></jmol> 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 <scene name='1a0s/Hidrophobic1/1'>see</scene> 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 <scene name='99/995028/Pacupp/2'>visualizing channels</scene> with pseudoatoms. In an alternative visualization, channels are shown as <scene name='41/411405/Channels/3'>surfaces</scene>, 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.

[[Image:Porin tunnels sliced.gif]]
</StructureSection>
== 3D structures of Porin ==
[[Porin 3D structures]]

==Acknowledgement==

The scene showing channels as pseudoatoms is from a page ([[User:Eric_Martz/Sandbox_19]]) made by Eric Martz. Eric also helped creating the surface rendition of the channels (technical details here: [[Image:Tunnels.jvxl]]).


==References==
<references />

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