An arginine ladder in OprP mediates phosphate-specific transfer across the outer membrane.
Moraes, T.F., Bains, M., Hancock, R.E., Strynadka, N.C.(2007) Nat.Struct.Mol.Biol. 14: 85-87
- PubMed: 17187075 
- DOI: 10.1038/nsmb1189
- PubMed Abstract: 
The outer membrane protein OprP mediates the transport of essential phosphate anions into the pathogenic bacterium Pseudomonas aeruginosa. Here we report the crystallographic structure of trimeric OprP at 1.9-A resolution, revealing an unprecedented ...