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<StructureSection load='' size='450' side='right' scene='Porin/Cv/1' caption='E. coli OmpC is a trimeric transmembrane protein with a porin fold (PDB code [[2j1n]])'>
[[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 ==
== 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).  
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>.


'''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.
*'''Maltoporin''' (LamB) facilitates the diffusion of maltodextrin across the membrane<ref>PMID:12003940</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>.


'''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.


See more details in<br />
For discussion of specific porins, see<br />
*[[Mycobacterium tuberculosis ArfA Rv0899]] for OmpA type<br />
*[[Mycobacterium tuberculosis ArfA Rv0899]] for OmpA type<br />
*[[Osmoporin OmpC (E. coli)]]<br />
*[[Osmoporin OmpC (E. coli)]]<br />
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== Structure ==
== 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>.  
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>.  


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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.  
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.  




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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.
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 2j1n channels.gif]]
[[Image:Porin tunnels sliced.gif]]


== 3D structures of Porin ==
== 3D structures of Porin ==

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Alexander Berchansky, Michal Harel, Jaime Prilusky, Joel L. Sussman, Karsten Theis
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