title: Structure of the secretion domain of HxuA from Haemophilus influenzae.
abstract: Haemophilus influenzae HxuA is a cell-surface protein with haem-haemopexin binding activity which is key to haem acquisition from haemopexin and thus is one of the potential sources of haem for this microorganism. HxuA is secreted by its specific transporter HxuB. HxuA/HxuB belongs to the so-called two-partner secretion systems (TPSs) that are characterized by a conserved N-terminal domain in the secreted protein which is essential for secretion. Here, the 1.5 Å resolution structure of the secretion domain of HxuA, HxuA301, is reported. The structure reveals that HxuA301 folds into a β-helix domain with two extra-helical motifs, a four-stranded β-sheet and an N-terminal cap. Comparisons with other structures of TpsA secretion domains are reported. They reveal that despite limited sequence identity, strong structural similarities are found between the β-helix motifs, consistent with the idea that the TPS domain plays a role not only in the interaction with the specific TpsB partners but also as the scaffold initiating progressive folding of the TpsA proteins at the bacterial surface.
authors: Institut de Recherche Interdisciplinaire, IRI USR 3078 CNRS-Université Lille Nord de France, Parc CNRS de la Haute Borne, 50 Avenue de Halley, 59658 Villeneuve d'Ascq, France.
authors: Stéphanie
authors: S
authors: Baelen
authors: Frédérique
authors: F
authors: Dewitte
authors: Bernard
authors: B
authors: Clantin
authors: Vincent
authors: V
authors: Villeret
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D058947:Bacterial Secretion Systems / Q000235:genetics; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D006193:Haemophilus influenzae / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006466:Hemopexin / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D040681:Structural Homology, Protein
chemical_list: D001425:Bacterial Outer Membrane Proteins; D058947:Bacterial Secretion Systems; D002352:Carrier Proteins; D011994:Recombinant Proteins; D006418:Heme; D006466:Hemopexin
keywords: HxuA; TPS; secretion system; β-helix