Structure of the secretion domain of HxuA from Haemophilus influenzae
Résumé
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.
Mots clés
Amino Acid Sequence
Gene Expression
Bacterial Outer Membrane Proteins
Protein Structure
Secondary
Bacterial Secretion Systems
X-ray Crystallography
Escherichia coli
Models
Molecular
Molecular Sequence Data
Hemopexin
secretion system
Recombinant Proteins
Haemophilus influenzae
Sequence Alignment
TPS
Heme
Protein Binding
β-helix
Protein Interaction Domains and Motifs
Structural Homology
Protein
HxuA
Carrier Proteins