title: The structure of HasB reveals a new class of TonB protein fold.
abstract: TonB is a key protein in active transport of essential nutrients like vitamin B12 and metal sources through the outer membrane transporters of Gram-negative bacteria. This inner membrane protein spans the periplasm, contacts the outer membrane receptor by its periplasmic domain and transduces energy from the cytoplasmic membrane pmf to the receptor allowing nutrient internalization. Whereas generally a single TonB protein allows the acquisition of several nutrients through their cognate receptor, in some species one particular TonB is dedicated to a specific system. Despite a considerable amount of data available, the molecular mechanism of TonB-dependent active transport is still poorly understood. In this work, we present a structural study of a TonB-like protein, HasB dedicated to the HasR receptor. HasR acquires heme either free or via an extracellular heme transporter, the hemophore HasA. Heme is used as an iron source by bacteria. We have solved the structure of the HasB periplasmic domain of Serratia marcescens and describe its interaction with a critical region of HasR. Some important differences are observed between HasB and TonB structures. The HasB fold reveals a new structural class of TonB-like proteins. Furthermore, we have identified the structural features that explain the functional specificity of HasB. These results give a new insight into the molecular mechanism of nutrient active transport through the bacterial outer membrane and present the first detailed structural study of a specific TonB-like protein and its interaction with the receptor.
authors.affiliation: Institut Pasteur, Unité de Résonance Magnétique Nucléaire des Biomolécules, Département de Biologie Structurale et Chimie, Paris, France.
authors.forename: Gisele Cardoso
authors.initials: GC
authors.lastname: de Amorim
authors.forename: Ada
authors.initials: A
authors.lastname: Prochnicka-Chalufour
authors.forename: Philippe
authors.initials: P
authors.lastname: Delepelaire
authors.forename: Julien
authors.initials: J
authors.lastname: Lefèvre
authors.forename: Catherine
authors.initials: C
authors.lastname: Simenel
authors.forename: Cécile
authors.initials: C
authors.lastname: Wandersman
authors.forename: Muriel
authors.initials: M
authors.lastname: Delepierre
authors.forename: Nadia
authors.initials: N
authors.lastname: Izadi-Pruneyre
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D016415:Sequence Alignment
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; C447836:HasB protein, Serratia marcescens; D008565:Membrane Proteins; D010455:Peptides; C057616:tonB protein, Bacteria