An arginine ladder in OprP mediates phosphate-specific transfer across the outer membrane

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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-Å resolution, revealing an unprecedented 9-residue arginine 'ladder' that spans from the extracellular surface down through a constriction zone where phosphate is coordinated. Lysine residues coat the inner periplasmic surface, creating an 'electropositive sink' that pulls the phosphates through the eyelet and into the cell.

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Figure 1: Overall structure of OprP.
Figure 2: Mechanism of phosphate transport.

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We thank C. Egli and N. Martin for valuable discussion and the staff at the Advanced Light Source beamline 8.2.2 for data collection time and assistance. T.F.M. is supported by a Michael Smith Foundation for Health Research (MSFHR) postdoctoral fellowship. N.C.J.S. thanks the Howard Hughes International Scholar program and the Canadian Institutes of Health Research (CIHR) for funding and the Canadian Foundation for Innovation and the MSFHR for infrastructure support. R.E.W.H. thanks the CIHR for funding, the Canadian Cystic Fibrosis Foundation and the US Cystic Fibrosis Foundation. N.C.J.S. is a MSFHR Senior Scholar, CIHR Investigator and Howard Hughes Medical Institute International Scholar. R.E.W.H. is a CIHR Investigator.

Author information

M.B. purified and crystallized proteins; T.F.M. performed crystal optimization and X-ray structure determination; T.F.M., R.E.W.H. and N.C.J.S. were involved in the structural analysis and discussion.

Correspondence to Natalie C J Strynadka.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Fig. 1

Secondary structural elements of OprP. (PDF 222 kb)

Supplementary Table 1

Data collection, phasing and refinement statistics. (PDF 79 kb)

Supplementary Methods (PDF 118 kb)

Supplementary Discussion (PDF 79 kb)

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