Functional Diversity of Heat-labile Toxins (LT) Produced by Enterotoxigenic Escherichia coli: DIFFERENTIAL ENZYMATIC AND IMMUNOLOGICAL ACTIVITIES OF LT1 (hLT) AND LT4 (pLT)

• Published in: The Journal of biological chemistry Vol. 286; no. 7; pp. 5222 - 5233
• Main Authors: Rodrigues, Juliana F, Mathias-Santos, Camila, Sbrogio-Almeida, Maria Elisabete, Amorim, Jaime H, Cabrera-Crespo, Joaquim, Balan, Andrea, Ferreira, Luís C.S
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 18.02.2011
• Subjects: Active sites; Adjuvants; Adjuvants, Immunologic - genetics; Adjuvants, Immunologic - metabolism; ADP-ribosylation; Amino Acid Substitution; Animals; Arginine; Bacterial Toxins - genetics; Bacterial Toxins - immunology; Bacterial Toxins - metabolism; CD8 antigen; CD8-Positive T-Lymphocytes - immunology; CD8-Positive T-Lymphocytes - metabolism; Cell activation; Cell Line, Tumor; Cyclic AMP; Cyclic AMP - genetics; Cyclic AMP - immunology; Cyclic AMP - metabolism; Cytotoxicity; Diarrhea; Enterotoxigenic Escherichia coli - immunology; Enterotoxigenic Escherichia coli - metabolism; Enterotoxigenic Escherichia coli - pathogenicity; Enterotoxins - genetics; Enterotoxins - immunology; Enterotoxins - metabolism; Escherichia coli; Escherichia coli Proteins - genetics; Escherichia coli Proteins - immunology; Escherichia coli Proteins - metabolism; Female; Humans; Lymphocytes T; Lysine; Mice; Microbiology; Mucosa; Mutation, Missense; Pathogenicity; Polymorphism, Genetic; Species Specificity; Swine; Th1 Cells - immunology; Th1 Cells - metabolism; Toxicity; Toxins; Vaccines
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M110.173682

Heat-labile toxins (LTs) have ADP-ribosylation activity and induce the secretory diarrhea caused by enterotoxigenic Escherichia coli (ETEC) strains in different mammalian hosts. LTs also act as adjuvants following delivery via mucosal, parenteral, or transcutaneous routes. Previously we have shown that LT produced by human-derived ETEC strains encompass a group of 16 polymorphic variants, including the reference toxin (LT1 or hLT) produced by the H10407 strain and one variant that is found mainly among bacterial strains isolated from pigs (LT4 or pLT). Herein, we show that LT4 (with six polymorphic sites in the A (K4R, K213E, and N238D) and B (S4T, A46E, and E102K) subunits) displays differential in vitro toxicity and in vivo adjuvant activities compared with LT1. One in vitro generated LT mutant (LTK4R), in which the lysine at position 4 of the A subunit was replaced by arginine, showed most of the LT4 features with an ~10-fold reduction of the cytotonic effects, ADP-ribosylation activity, and accumulation of intracellular cAMP in Y1 cells. Molecular dynamic studies of the A subunit showed that the K4R replacement reduces the N-terminal region flexibility and decreases the catalytic site crevice. Noticeably, LT4 showed a stronger Th1-biased adjuvant activity with regard to LT1, particularly concerning activation of cytotoxic CD8⁺ T lymphocytes when delivered via the intranasal route. Our results further emphasize the relevance of LT polymorphism among human-derived ETEC strains that may impact both the pathogenicity of the bacterial strain and the use of these toxins as potential vaccine adjuvants.