{PDOC00498}
{PS00576; GRAM_NEG_PORIN}
{BEGIN}
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* General diffusion Gram-negative porins signature *
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The  outer membrane  of  Gram-negative bacteria acts as a molecular filter for
hydrophilic compounds.  Proteins, known as porins [1], are responsible for the
'molecular sieve' properties of the outer membrane.  Porins  form large water-
filled channels which allows the  diffusion  of hydrophilic molecules into the
periplasmic space. Some porins form general diffusion channels that allows any
solutes  up to  a certain  size (that size is known as the exclusion limit) to
cross the membrane, while other porins  are  specific for a solute and contain
a binding site for that solute inside the pores  (these are known as selective
porins).  As porins are the major outer membrane proteins,  they also serve as
receptor sites for the binding of phages and bacteriocins.

General diffusion porins generally assemble as  trimer in the membrane and the
transmembrane core of these proteins  is composed  exclusively of beta strands
[2]. It has been shown [3] that a  number  of general porins are  evolutionary
related, these porins are:

 - Enterobacteria phoE.
 - Enterobacteria ompC.
 - Enterobacteria ompF.
 - Enterobacteria nmpC.
 - Bacteriophage PA-2 LC.
 - Neisseria PI.A.
 - Neisseria PI.B.

As a  signature  pattern  we  selected  a  conserved  region,  located  in the
C-terminal part of these proteins, which spans two putative transmembrane beta
strands.

-Consensus pattern: [LIVMFY]-x(2)-G-x(2)-Y-x-F-x-K-x(2)-[SN]-[STAV]-[LIVMFYW]-
                    V
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.
-Last update: July 1999 / Pattern and text revised.

[ 1] Benz R., Bauer K.
     "Permeation of hydrophilic molecules through the outer membrane of
     gram-negative bacteria. Review on bacterial porins."
     Eur. J. Biochem. 176:1-19(1988).
     PubMed=2901351
[ 2] Jap B.K., Walian P.J.
     "Biophysics of the structure and function of porins."
     Q. Rev. Biophys. 23:367-403(1990).
     PubMed=2178269
[ 3] Jeanteur D., Lakey J.H., Pattus F.
     "The bacterial porin superfamily: sequence alignment and structure
     prediction."
     Mol. Microbiol. 5:2153-2164(1991).
     PubMed=1662760

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