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)


This family belongs to the Outer Membrane Pore-forming Protein I (OMPP-I) Superfamily .
 

References:

Manilla-Pérez, E., C. Reers, M. Baumgart, S. Hetzler, R. Reichelt, U. Malkus, R. Kalscheuer, M. Wältermann, and A. Steinbüchel. (2010). Analysis of lipid export in hydrocarbonoclastic bacteria of the genus Alcanivorax: identification of lipid export-negative mutants of Alcanivorax borkumensis SK2 and Alcanivorax jadensis T9. J. Bacteriol. 192: 643-656.
Rehm, B.H., G. Boheim, J. Tommassen, and U.K. Winkler. (1994). Overexpression of algE in Escherichia coli: subcellular localization, purification, and ion channel properties. J. Bacteriol. 176: 5639-5647.
Rehm, B.H.A. (1996). The Azotobacter vinelandii gene algJ encodes an outer-membrane protein presumably involved in export of alginate. Microbiol. 142: 873-880.
Rehman ZU. and Rehm BH. (2013). Dual roles of Pseudomonas aeruginosa AlgE in secretion of the virulence factor alginate and formation of the secretion complex. Appl Environ Microbiol. 79(6):2002-11.
Examples:

TC#NameOrganismal TypeExample
1.B.13.1.1

Alginate export porin, AEP or AlgE (Rehm et al. 1994).  A monomeric 18 stranded beta-barrel that is part of a multicomponent, two membrane, envelope-spanning complex that includes AlgK, AlgX and Alg44 (Rehman and Rehm 2013).

γ-Proteobacteria

AlgE of Pseudomonas aeruginosa

 
1.B.13.1.2

Porin, AlgE (AlgJ)

γ-Proteobacteria

Porin of Azotobacter vinelandii

 
1.B.13.1.3

Putative porin

β-Proteobacteria

Putative porin of Burkholderiales bacterium

 
1.B.13.1.4

Putative porin

Aquificae

Putative porin of Thermovibrio ammonificans

 
1.B.13.1.5

Putative porin

ε-Proteobacteria

Putative porin of Nitratiruptor sp. SB155-2

 
1.B.13.1.6

Putative porin

γ-Proteobacterial

Putative porin of E. coli

 
1.B.13.1.7

Alginate export porin of 460 aas.  May also export neutral lipids such as triacylglycerols, wax esters, and polyhydroxyalkanoates (Manilla-Pérez et al. 2010).

Proteobacteria

AlgE of Alcanivorax borkumensis

 
Examples:

TC#NameOrganismal TypeExample
1.B.13.2.1

Putative porin

Spirochaetes

Putative porin of Turneriella parva

 
1.B.13.2.2

Putative porin of 536 aas

Spirochaetes

Putative porin of Turneriella parva

 
Examples:

TC#NameOrganismal TypeExample
1.B.13.3.1

Putative porin

Verucomicrobia

Putative porin of Pedosphaera parvula

 
1.B.13.3.2

Putative porin of 455 aas

Bacteroidetes

Putative porin of Flavobacterium johnsoniae

 
1.B.13.3.3

Putative porin

Acidobacteria

Putative porin of Solibacter usitatus

 
1.B.13.3.4

Putative porin of 447 aas

Proteobacteria

Putative porin of Brucella abortus

 
1.B.13.3.5

PF13372 domain protein of 609 aas

Spirochaetes

PF13372 domain protein of Leptspira interrogans