Integrins are important mammalian receptors involved in normal cellular functions as well as pathogenesis of chronic inflammation and cancer. We propose that integrins are exploited by the gastric pathogen and type-1 carcinogen Helicobacter pylori for injection of the bacterial oncoprotein cytotoxin-associated gene A (CagA) into gastric epithelial cells. Virulent H. pylori express a type-IV secretion pilus that injects CagA into the host cell; CagA then becomes tyrosine-phosphorylated by Src family kinases. However, the identity of the host cell receptor involved in this process has remained unknown. Here we show that the H. pylori CagL protein is a specialized adhesin that is targeted to the pilus surface, where it binds to and activates integrin alpha5beta1 receptor on gastric epithelial cells through an arginine-glycine-aspartate motif. This interaction triggers CagA delivery into target cells as well as activation of focal adhesion kinase and Src. Our findings provide insights into the role of integrins in H.-pylori-induced pathogenesis. CagL may be exploited as a new molecular tool for our further understanding of integrin signalling.

Interactions between the extracellular matrix and membrane proteins are of importance for cell adhesion, tissue formation, and transmembrane signaling processes. Among cell adhesion molecules, integrins occupy a highly prominent position. Many integrins, among them a 5 b 1 and a V b 3 , recognize the tripeptide sequence -Arg-Gly-Asp-(RGD) in their ligands. The discovery of the role of the RGD sequence in cell-cell and cell-matrix interactions prompted the development of a broad variety of RGD peptides and peptidomimetics for potential therapeutic applications. Soluble derivatives of these compounds are able to competitively inhibit the interaction between an RGD-containing protein and its integrin counterpart, whereas immobilized RGD peptides support cell attachment, for example, to artificial implants.

Der Einbau des rigiden Bausteins (+)‐β‐Acc (Acc=Aminocyclopropancarbonsäure) in ein cyclisches RGD‐Peptid führt wegen der hierdurch induzierten konformativen Einschränkungen zu hoch affinen Liganden für das Integrin αvβ3. Die Peptide 1 und 2 enthalten die enantiomeren Bausteine (+)‐ (blau) bzw. (−)‐β‐Acc (rot). Das aktivere Peptid 1 inhibiert die αvβ3‐vermittelte Zelladhäsion an Vitronectin mit einem IC50‐Wert von 20 nm.

Novel efficient and robust affinity chromatography material: There are several strategies known for the purification of integrins by affinity chromatography, but the disadvantages of common strategies like insufficient selectivity or compelling conditions for the elution still require alternatives. A new strategy, based on the immobilized C‐terminally modified peptide Ac‐Gly‐Ala‐c‐(CysSS‐Arg‐Arg‐Glu‐Thr‐Ala‐Trp‐Ala‐CysSS)‐Gly‐Ala‐O(CH2CH2O)2CH2CH2‐NH2 allows for the affinity purification of the integrin α5β1. While RGD peptides have been proven in the past to be inappropriate for selective purification of integrins by affinity chromatography, the new peptide can be efficiently used for selective enrichment of the integrin α5β1. It is a specific ligand of the target protein, but does not contain an RGD sequence. The application of well‐characterized affinity chromatography material with a site‐specifically immobilized peptide allows to obtain integrin α5β1 in a single chromatography step without contamination by other integrins. This process combines the advantages of a selective and monospecific protein‐ligand recognition with mild elution conditions and a low sensitivity of the immobilized ligand with respect to column regeneration.