The heme transfer from the soluble HasA hemophore to its membrane-bound receptor HasR is driven by protein-protein interaction from a high to a lower affinity binding site.
HasA is an extracellular heme binding protein, and HasR is an outer membrane receptor protein from Serratia marcescens. They are the initial partners of a heme internalization system allowing S. marcescens to scavenge heme at very low concentrations due to the very high affinity of HasA for heme (Ka = 5,3 x 10(10) m(-1)). Heme is then transferred to HasR, which has a lower affinity for heme. The mechanism of the heme transfer between HasA and HasR is largely unknown. HasR has been overexpressed and purified in holo and apo forms. It binds one heme molecule with a Ka of 5 x 10(6) m(-1) and shows the characteristic absorbance spectrum of a low spin heme iron. Both holoHasA and apoHasA bind tightly to apoHasR in a 1:1 stoichiometry. In this study we show that heme transfer occurs in vitro in the purified HasA.HasR complex, demonstrating that heme transfer is energy- and TonB complex-independent and driven by a protein-protein interaction. We also show that heme binding to HasR involves two conserved histidine residues.
Izadi-Pruneyre
Nadia
N
Unité des Membranes Bactériennes, CNRS URA 2172 Département de Microbiologie, Institut Pasteur, 75724 Paris Cedex 15 France.
Huché
Frédéric
F
Lukat-Rodgers
Gudrun S
GS
Lecroisey
Anne
A
Gilli
Robert
R
Rodgers
Kenton R
KR
Wandersman
Cécile
C
Delepelaire
Philippe
P
D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000502:physiology; D001665:Binding Sites; D002151:Calorimetry; D002352:Carrier Proteins / Q000737:chemistry / Q000502:physiology*; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry / Q000502:physiology*; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000378:metabolism; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman; D013816:Thermodynamics; D014466:Ultraviolet Rays
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; C093956:HasA protein, Serratia marcescens; D008565:Membrane Proteins; D011956:Receptors, Cell Surface