Isolation and characterization of an extracellular haem‐binding protein from Pseudomonas aeruginosa that shares function and sequence similarities with the Serratia marcescens HasA haemophore

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Abstract
The major mechanism by which bacteria acquire free or haemoglobin‐bound haem involves direct binding to specific outer membrane receptors. Serratia marcescens also secretes a haem‐binding protein, HasA, which functions as a haemophore that catches haem and shuttles it to a cell surface specific outer membrane receptor, HasR. We report the isolation and characterization of hasAp, a gene from Pseudomonas aeruginosa. HasAp is an iron‐regulated extracellular haem‐binding protein that shares about 50% identity with HasA. HasAp is required for P. aeruginosa utilization of haemoglobin iron. It can replace HasA for HasR‐dependent haemoblobin acquisition in a system reconstituted in Escherichia coli. HasAp, like HasA, lacks a signal peptide and is secreted by an ABC transporter. These findings show that haemophore‐dependent haem acquisition is not unique to S. marcescens.