NORMAL GENOMIC

• Lins L, Brasseur R
• Tilted peptides: a structural motif involved in protein membrane insertion?
• J Pept Sci. 2008; 14: 416-22
• Display abstract

• Tilted peptides are short hydrophobic protein fragments characterized by an asymmetric distribution of their hydrophobic residues when helical. They are able to interact with a hydrophobic/hydrophilic interface (such as a lipid membrane) and to destabilize the organized system into which they insert. They were detected in viral fusion proteins and in proteins involved in different biological processes involving membrane insertion or translocation of the protein in which they are found. In this paper, we have analysed different protein domains related to membrane insertion with regard to their tilted properties. They are the N-terminal signal peptide of the filamentous haemagglutinin (FHA), a Bordetella pertussis protein secreted in high amount and the hydrophobic domain from proteins forming pores (i.e. ColIa, Bax and Bcl-2). From the predictions and the experimental approaches, we suggest that tilted peptides found in those proteins could have a more general role in the mechanism of insertion/translocation of proteins into/across membranes. For the signal sequences, they could help the protein machinery involved in protein secretion to be more active. In the case of toroidal pore formation, they could disturb the lipids, facilitating the insertion of the other more hydrophilic helices.

• Muller A, Leon-Kempis Mdel R, Dodson E, Wilson KS, Wilkinson AJ, Kelly DJ
• A bacterial virulence factor with a dual role as an adhesin and a solute-binding protein: the crystal structure at 1.5 A resolution of the PEB1a protein from the food-borne human pathogen Campylobacter jejuni.
• J Mol Biol. 2007; 372: 160-71
• Display abstract

• The PEB1a protein is an antigenic factor exposed on the surface of the food-borne human pathogen Campylobacter jejuni, which has a major role in adherence and host colonisation. PEB1a is also the periplasmic binding protein component of an aspartate/glutamate ABC transporter essential for optimal microaerobic growth on these dicarboxylic amino acids. Here, we report the crystal structure of PEB1a at 1.5 A resolution. The protein has a typical two-domain alpha/beta structure, characteristic of periplasmic extracytoplasmic solute receptors and a chain topology related to the type II subfamily. An aspartate ligand, clearly defined by electron density in the interdomain cleft, forms extensive polar interactions with the protein, the majority of which are made with the larger domain. Arg89 and Asp174 form ion-pairing interactions with the main chain alpha-carboxyl and alpha-amino-groups, respectively, of the ligand, while Arg67, Thr82, Lys19 and Tyr156 co-ordinate the ligand side-chain carboxyl group. Lys19 and Arg67 line a positively charged groove, which favours binding of Asp over the neutral Asn. The ligand-binding cleft is of sufficient depth to accommodate a glutamate. This is the first structure of an ABC-type aspartate-binding protein, and explains the high affinity of the protein for aspartate and glutamate, and its much weaker binding of asparagine and glutamine. Stopped-flow fluorescence spectroscopy indicates a simple bimolecular mechanism of ligand binding, with high association rate constants. Sequence alignments and phylogenetic analyses revealed PEB1a homologues in some Gram-positive bacteria. The alignments suggest a more distant homology with GltI from Escherichia coli, a known glutamate and aspartate-binding protein, but Lys19 and Tyr156 are not conserved in GltI. Our results provide a structural basis for understanding both the solute transport and adhesin/virulence functions of PEB1a.