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Publication Abstract from PubMed

Gram-negative bacteria use specific heme uptake systems, relying on outer membrane receptors and excreted heme-binding proteins (hemophores) to scavenge and actively transport heme. To unravel the unknown molecular details involved, we present 3 structures of the Serratia marcescens receptor HasR in complex with its hemophore HasA. The transfer of heme over a distance of 9 A from its high-affinity site in HasA into a site of lower affinity in HasR is coupled with the exergonic complex formation of the 2 proteins. Upon docking to the receptor, 1 of the 2 axial heme coordinations of the hemophore is initially broken, but the position and orientation of the heme is preserved. Subsequently, steric displacement of heme by a receptor residue ruptures the other axial coordination, leading to heme transfer into the receptor.

Heme uptake across the outer membrane as revealed by crystal structures of the receptor-hemophore complex.,Krieg S, Huche F, Diederichs K, Izadi-Pruneyre N, Lecroisey A, Wandersman C, Delepelaire P, Welte W Proc Natl Acad Sci U S A. 2009 Jan 27;106(4):1045-50. Epub 2009 Jan 14. PMID:19144921^[3]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.