1.B.13 The Alginate Export Porin (AEP) Family
Only two proteins of the AEP family have been sequenced, AlgE of Pseudomonas aeruginosa and AlgJ of Azotobacter vinelandii. Both proteins are believed to export the acidic polysaccharide, alginate, across the outer membrane of these Gram-negative bacteria. These proteins possess 490 and 484 amino acyl residues, are 50% identical, and are predicted to span the outer membrane 18 times as β-strands, thereby forming a β-barrel. The P. aeruginosa protein has been shown to form an anion-selective channel after incorporation into an artificial planar lipid bilayer. It may function in the export of polymannuronic acid, a precursor of alginate.
The generalized transport reaction normally catalyzed by proteins of the AEP family is:
Alginate (periplasm) → Alginate (out)