General bacterial porins are a family of proteins from the outer membrane 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 solutes 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. Members of this family, similar to all porins, have been shown to form ß-barrels with 16 beta strands.

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