Comparative analysis of structural and dynamic properties of the loaded and unloaded hemophore HasA: functional implications.
A heme-acquisition system present in several Gram-negative bacteria requires the secretion of hemophores. These extracellular carrier proteins capture heme and deliver it to specific outer membrane receptors. The Serratia marcescens HasA hemophore is a monodomain protein that binds heme with a very high affinity. Its alpha/beta structure, as that of its binding pocket, has no common features with other iron- or heme-binding proteins. Heme is held by two loops L1 and L2 and coordinated to iron by an unusual ligand pair, H32/Y75. Two independent regions of the hemophore beta-sheet are involved in HasA-HasR receptor interaction. Here, we report the 3-D NMR structure of apoHasA and the backbone dynamics of both loaded and unloaded hemophore. While the overall structure of HasA is very similar in the apo and holo forms, the hemophore presents a transition from an open to a closed form upon ligand binding, through a large movement, of up to 30 A, of loop L1 bearing H32. Comparison of loaded and unloaded HasA dynamics on different time scales reveals striking flexibility changes in the binding pocket. We propose a mechanism by which these structural and dynamic features provide the dual function of heme binding and release to the HasR receptor.
Wolff
Nicolas
N
Unité de RMN des Biomolécules, CNRS URA 2185, Département de Biologie Structurale et de Chimie, Institut Pasteur, 75724 Paris Cedex 15, France. wolff@pasteur.fr
Izadi-Pruneyre
Nadia
N
Couprie
Joël
J
Habeck
Michael
M
Linge
Jens
J
Rieping
Wolfgang
W
Wandersman
Cécile
C
Nilges
Michael
M
Delepierre
Muriel
M
Lecroisey
Anne
A
D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; D008024:Ligands; D008027:Light; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012542:Scattering, Radiation; D012706:Serratia marcescens / Q000737:chemistry*
D001426:Bacterial Proteins; D002352:Carrier Proteins; C093956:HasA protein, Serratia marcescens; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; D008024:Ligands; D008565:Membrane Proteins; D006418:Heme