Display Options Spacefill Backbone Wireframe Sticks Strands Show b-strand Show b-turn The Porins The porins are a family of proteins which are found in the outer membrane of Gram-negative bacteria. Their role is to provide a pathway for the diffusion of small hydrophilic compounds into and out of the cell. General properties of porins include a high thermal stability and resistance to protease and detergent degradation, essential for the survival of Gram-negative bacteria in harsh environments such as the intestinal tract (Schirmer, T. and Rosenbusch, J. P., Curr. Opinion Struct. Biol., 1, 539-545 (1991)). Most porin channels show a weak ion selectivity and moderate voltage gating behaviour. Underlying the high stability of these proteins is their unusual structure, consisting of a 16-stranded antiparallel b-barrel (Cowan, S. W. et al, Nature, 358, 727-733 (1992)) with a shear number of 20. Extra stability is derived from the formation of a salt bridge between the N- and C-termini to produce an essentially closed structure, with the tilt of the strands at 35-50 deg. relative to the barrel axis. The exits of the channel are bordered by b-turns, although there is a marked difference between the two ends. The extracellular end or rough end is marked by the presence of extended loop structures, some of which protrude into the channel pore and provide a means of regulating channel selectivity. Short b-turns are found at the intracellular end or smooth end of the porin channel (see the display opposite, for example). The pore itself is irregular in shape due to the extended loops of the rough end, but is predominantly populated with polar residues and is 22 Angstroms in diameter at its widest point.
Spacefill Backbone Wireframe Sticks Strands Show b-strand Show b-turn The Porins The porins are a family of proteins which are found in the outer membrane of Gram-negative bacteria. Their role is to provide a pathway for the diffusion of small hydrophilic compounds into and out of the cell. General properties of porins include a high thermal stability and resistance to protease and detergent degradation, essential for the survival of Gram-negative bacteria in harsh environments such as the intestinal tract (Schirmer, T. and Rosenbusch, J. P., Curr. Opinion Struct. Biol., 1, 539-545 (1991)). Most porin channels show a weak ion selectivity and moderate voltage gating behaviour. Underlying the high stability of these proteins is their unusual structure, consisting of a 16-stranded antiparallel b-barrel (Cowan, S. W. et al, Nature, 358, 727-733 (1992)) with a shear number of 20. Extra stability is derived from the formation of a salt bridge between the N- and C-termini to produce an essentially closed structure, with the tilt of the strands at 35-50 deg. relative to the barrel axis. The exits of the channel are bordered by b-turns, although there is a marked difference between the two ends. The extracellular end or rough end is marked by the presence of extended loop structures, some of which protrude into the channel pore and provide a means of regulating channel selectivity. Short b-turns are found at the intracellular end or smooth end of the porin channel (see the display opposite, for example). The pore itself is irregular in shape due to the extended loops of the rough end, but is predominantly populated with polar residues and is 22 Angstroms in diameter at its widest point.
Show b-strand Show b-turn The Porins The porins are a family of proteins which are found in the outer membrane of Gram-negative bacteria. Their role is to provide a pathway for the diffusion of small hydrophilic compounds into and out of the cell. General properties of porins include a high thermal stability and resistance to protease and detergent degradation, essential for the survival of Gram-negative bacteria in harsh environments such as the intestinal tract (Schirmer, T. and Rosenbusch, J. P., Curr. Opinion Struct. Biol., 1, 539-545 (1991)). Most porin channels show a weak ion selectivity and moderate voltage gating behaviour. Underlying the high stability of these proteins is their unusual structure, consisting of a 16-stranded antiparallel b-barrel (Cowan, S. W. et al, Nature, 358, 727-733 (1992)) with a shear number of 20. Extra stability is derived from the formation of a salt bridge between the N- and C-termini to produce an essentially closed structure, with the tilt of the strands at 35-50 deg. relative to the barrel axis. The exits of the channel are bordered by b-turns, although there is a marked difference between the two ends. The extracellular end or rough end is marked by the presence of extended loop structures, some of which protrude into the channel pore and provide a means of regulating channel selectivity. Short b-turns are found at the intracellular end or smooth end of the porin channel (see the display opposite, for example). The pore itself is irregular in shape due to the extended loops of the rough end, but is predominantly populated with polar residues and is 22 Angstroms in diameter at its widest point.
The Porins The porins are a family of proteins which are found in the outer membrane of Gram-negative bacteria. Their role is to provide a pathway for the diffusion of small hydrophilic compounds into and out of the cell. General properties of porins include a high thermal stability and resistance to protease and detergent degradation, essential for the survival of Gram-negative bacteria in harsh environments such as the intestinal tract (Schirmer, T. and Rosenbusch, J. P., Curr. Opinion Struct. Biol., 1, 539-545 (1991)). Most porin channels show a weak ion selectivity and moderate voltage gating behaviour. Underlying the high stability of these proteins is their unusual structure, consisting of a 16-stranded antiparallel b-barrel (Cowan, S. W. et al, Nature, 358, 727-733 (1992)) with a shear number of 20. Extra stability is derived from the formation of a salt bridge between the N- and C-termini to produce an essentially closed structure, with the tilt of the strands at 35-50 deg. relative to the barrel axis. The exits of the channel are bordered by b-turns, although there is a marked difference between the two ends. The extracellular end or rough end is marked by the presence of extended loop structures, some of which protrude into the channel pore and provide a means of regulating channel selectivity. Short b-turns are found at the intracellular end or smooth end of the porin channel (see the display opposite, for example). The pore itself is irregular in shape due to the extended loops of the rough end, but is predominantly populated with polar residues and is 22 Angstroms in diameter at its widest point.