Crystal structure of CagL from Helicobacter pylori K74 strain

• Culture media alterations help to obtain CagLK74 in soluble form to avoid refolding.
• CagLK74 folds to an elongated six-helix bundle with a long rigid α2 helix.
• The RGD motif found in the rigid α2 is further stabilized by interactions with α1.
• CagLK74 RGD motif may be less flexible than canonical RGDs for integrin binding.

Helicobacter pylori (Hp) CagL is a component of the type IV secretion system (T4SS) and interacts with integrin in host cells through its flexible RGD domain to translocate CagA. Differences in CagL amino acid polymorphisms between Western and East-Asian Hps are correlated with clinical outcome. CagL of East-Asian clinical Hp isolate K74 (CagLK74) contains multiple residue variations upstream of RGD motif and has different integrin binding affinities compared to those of CagL from Western Hp 26695. Here, we report the crystal structure of CagLK74. The structure displayed a six-helix bundle including two short α-helices, and the RGD motif was found in the long rigid α2 helix flanked by the conserved protease-sensitive and RGD-helper sequences, as observed in CagL26695. However, two additional salt bridges were found between the helices compared with the CagL26695 structure, suggesting that the putative flexible region harboring the RGD motif may be more stable in this CagL variant.