Lectin PLL3, a Novel Monomeric Member of the Seven-Bladed β-Propeller Lectin Family

Abstract

The Photorhabdus species is a Gram-negative bacteria of the family Morganellaceae that is known for its mutualistic relationship with Heterorhabditis nematodes and pathogenicity toward insects. This study is focused on the characterization of the recombinant lectin PLL3 with an origin in P. laumondii subsp. laumondii. PLL3 belongs to the PLL family of lectins with a seven-bladed β-propeller fold. The binding properties of PLL3 were tested by hemagglutination assay, glycan array, isothermal titration calorimetry, and surface plasmon resonance, and its structure was determined by X-ray crystallography. Obtained data revealed that PLL3 binds similar carbohydrates to those that the other PLL family members bind, with some differences in the binding properties. PLL3 exhibited the highest affinity toward l-fucose and its derivatives but was also able to interact with O-methylated glycans and other ligands. Unlike the other members of this family, PLL3 was discovered to be a monomer, which might correspond to a weaker avidity effect compared to homologous lectins. Based on the similarity to the related lectins and their proposed biological function, PLL3 might accompany them during the interaction of P. laumondii with both the nematode partner and the insect host.Molecules 2019, 24, 4540 2 of 20 create together a nematobacterial complex, which is highly pathogenic for a wide range of insects, especially for their larval stages [2,4]. Infective juveniles (IJs), a specialized larval stadium of the Heterorhabditis nematode, attack the insect larva and release the Photorhabdus from its intestine into the insect haemocoel. Bacteria then multiply and produce various virulence factors (e.g., adhesins, toxins, proteases, and lipases) to overcome the host immune response. The insect host is killed within 48 h due to global septicaemia [2,5,6]. In addition, Photorhabdus produces special nutrients that are necessary for the nematode growth [2,5,7]. Heterorhabditis feeds on the insect tissues as well as on the Photorhabdus cells and undergoes several cycles of sexual reproduction. Once the nutrients are depleted, a new generation of IJs is created, which is associated with the Photorhabdus and leaves the cadaver to search for its next pray [2,4,5,8].The study of the relationship between Photorhabdus, nematodes, and insect can provide important information about prokaryotic involvement in two different symbioses such as mutualism and pathogenicity [2,4]. The interactions between the individual members of this complicated system are not fully understood; however, it is likely that part of them will include proteins on the cell surface. One group of such proteins are lectins, which are carbohydrate-binding proteins that have been demonstrated to play a crucial role in many physiological and pathophysiological processes [9,10]. Lectins are proteins without catalytic activity that are able to bind mono-and oligosaccharides reversibly and with high specificity [9][10][11]. Lectins are abundantly expressed in viruses, bacteria, and fungi ...

Visualization of hydrogen atoms in a perdeuterated lectin-fucose complex reveals key details of protein-carbohydrate interactions

“…This species can also adopt an alternative lifestyle in the soil, with positive influence on plant rhizosphere (Regaiolo et al, 2020). P. laumondii produces several lectins; three of them, PLL (Kumar et al, 2016), PLL2 (Fujdiarová et al, 2020), and PLL3 (Faltinek et al, 2019) having similar in sequences, have been recently characterized and are proposed to play important roles in the complex Photorhabdus life cycle. All three lectins bind L-fucose and their monomeric structure folds as a seven-bladed b propeller characteristic of this family of lectins.…”