General bacterial porin family

1pho :27-351 1iivA:27-378 1osmA:27-3631opfD:28-362 1mpf :28-362 2omf :28-3621gfm :28-362 1hxuA:28-362 1gfp :28-3621gfq :28-362 1hxxA:28-362 1bt9A:28-362General bacterial porins are a family of proteins from the outer membranes of Gram-negative bacteria. The porins act as molecular filters for hydrophilic compounds. They are responsible for the 'molecular sieve' properties of the outer membrane. Porins form large water-filled channels which allow the diffusion of hydrophilic molecules into the periplasmic space. Some porins form general diffusion channels that allow any solute up to a certain size (that size is known as the exclusion limit) to cross the membrane, while other porins are specific for one particular 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 bacterial porins are a family of proteins from the outer membranes of Gram-negative bacteria. The porins act as molecular filters for hydrophilic compounds. They are responsible for the 'molecular sieve' properties of the outer membrane. Porins form large water-filled channels which allow the diffusion of hydrophilic molecules into the periplasmic space. Some porins form general diffusion channels that allow any solute up to a certain size (that size is known as the exclusion limit) to cross the membrane, while other porins are specific for one particular 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 usually assemble as a trimer in the membrane, and the transmembrane core of these proteins is composed exclusively of beta strands. It has been shown that a number of porins are evolutionarily related, and these porins are: Porins are composed of β-strands, which are, in general, linked together by beta turns on the periplasmic side of the outer membrane and long loops on the external side of the membrane. The β strand lie in an antiparallel fashion and form a cylindrical tube, called a β-barrel. The amino acid composition of the porin β-strands are unique in that polar and non-polar residues alternate along them. This means that the non-polar residues face outwards so as to interact with the non-polar lipid membrane, whereas the polar residues face inwards into the center of the β-barrel to form the aqueous channel. The phospholipids that comprise the outer membrane give it the same semi-permeable characteristics as the cytoplasmic membrane