High Bacterial Agglutination Activity in a Single-CRD C-Type Lectin from Spodoptera exigua (Lepidoptera: Noctuidae)

Abstract

Lectins are carbohydrate-interacting proteins that play a pivotal role in multiple physiological and developmental aspects of all organisms. They can specifically interact with different bacterial and viral pathogens through carbohydrate-recognition domains (CRD). In addition, lectins are also of biotechnological interest because of their potential use as biosensors for capturing and identifying bacterial species. In this work, three C-type lectins from the Lepidoptera Spodoptera exigua were produced as recombinant proteins and their bacterial agglutination properties were characterized. The lowest protein concentration producing bacterial agglutination against a panel of different Gram+ and Gram- as well as their carbohydrate binding specificities was determined for the three lectins. One of these lectins, BLL2, was able to agglutinate cells from a broad range of bacterial species at an extremely low concentration, becoming a very interesting protein to be used as a biosensor or for other biotechnological applications involving bacterial capture.

Keywords: C-type lectin; CRD; E. coli; agglutination; bacterial detection.

Figure 1

Amino acidic sequences of the bracovirus-like lectins (BLL). (A) Phylogenetic relationship of the different BLLs detected in the transcriptome of Spodoptera exigua. Phylogenetic distance was calculated by the Maximum-likelihood method. Reliability of an inferred tree was determined using the bootstrap test (1000 replicates). For a clearer view of the branches, bootstrap values are reported over 100; (B) Amino acidic alignment of the three BLLs studied, indicating the presence of the predicted signal peptide (SP), the carbohydrate recognition domain (CRD), the ligand binding surface (LBS), and the conserved cysteine residues (♦).

Figure 2

Bacterial agglutination in the presence of the BLLs. Representative images of the agglutination of three types of bacteria ((A) E. coli dt-tomato; (B) B. thuringiensis GFP; (C) P. aeruginosa) in the presence of serial dilutions of the three BLLs. Controls of agglutination in the absence of Ca²⁺ (w/o Ca²⁺) are also shown.

Figure 3

Carbohydrates’ inhibition of bacterial agglutination in the presence of the BLLs. Representative images of the agglutination of two types of bacteria ((A) E. coli dt-tomato; (B) B. thuringiensis GFP) in the presence of different concentrations of carbohydrates. In the absence of inhibition by the carbohydrate, the maximum concentrations tested are shown.