Lectins are carbohydrate-interacting proteins involved in numerous processes in living organisms, including cell development, cell-cell communication, recognition of a pathogen by a host and vice versa. Frequently, single organism produces several different lectins and, especially in complex environments, single lectin might be involved in several processes. Photorhabdus is a genus of gram-negative bioluminescent bacteria living in a symbiosis with Heterorhabditis nematodes forming a highly entomopathogenic complex that is used in agriculture as a nature-based insecticide. Some members of Photorhabdus genus act as human pathogens as well. It is not surprising, that Photorhabdus bacteria encode several lectins in their genome [1-3].
There are several well-known specificities for lectins. Commonly studied are lectins recognizing l-fucose or sialic acid, saccharides that are found on mammalian tissues. However, in bacteria, fungi and invertebrates, many other potentially targeted saccharides exist. One such group of rarely studied saccharides are O-methylated glycans that are modified by methyl group on one or more of their hydroxyls [4]. They were recently described as pathogen-associated molecular patterns, i.e. molecules that serve for pathogen recognition. They were found in bacteria, fungi, plants, worms and molluscs but not in arthropods or mammals.
We analysed several homologous lectins from P. asymbiotica and P. laumondii revealing their ability to recognize O-methylated sugars. We examined the binding using glycan array, ITC and SPR techniques and investigated their effect on lectin-based stimulation of insect immune system. Since each of studied lectins harbours several binding sites of non-equal specificity, we also solved X-ray structure with a few O-methylated glycans. The combination of approaches allows us to investigate these interactions in further details. It may shed a light onto the complex interaction between Photorhabdus and its symbionts/hosts and possibly find applications in biotechnologies, clinical research and drug development.
This work was supported by the Czech Science Foundation (project 18-18964S) and by the MEYS of the Czech Republic under the project CEITEC 2020 (LQ1601). CIISB research infrastructure project LM2018127 funded by MEYS CR is also gratefully acknowledged for the financial support of the measurements at the CF Biomolecular Interactions and Crystallization, Nanobiotechnology CF, CF CELLIM and CF Proteomics at CEITEC (Brno, Czech Republic). We wish to thank the Helmholtz-Zentrum Berlin (Berlin-Adlershof, Germany) and DESY (Hamburg, Germany) for synchrotron radiation beam time and to thank to Nikolay Kondakov and Leonid Kononov for preparation of synthetic saccharides.