Heme uptake across the outer membrane as revealed by crystal structures of the receptor-hemophore complex.
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.
Krieg
Stefanie
S
Fachbereich Biologie, Universität Konstanz, 78457 Konstanz, Germany.
Huché
Frédéric
F
Diederichs
Kay
K
Izadi-Pruneyre
Nadia
N
Lecroisey
Anne
A
Wandersman
Cécile
C
Delepelaire
Philippe
P
Welte
Wolfram
W
D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001692:Biological Transport; D002151:Calorimetry; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D018360:Crystallography, X-Ray; D006418:Heme / Q000737:chemistry / Q000378:metabolism*; D000081062:Heme-Binding Proteins; D006420:Hemeproteins / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000378:metabolism; D012706:Serratia marcescens / Q000737:chemistry*; D013499:Surface Properties
D001059:Apoproteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; C093956:HasA protein, Serratia marcescens; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; D008024:Ligands; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D006418:Heme