Potential enzymatic degradation of various toxins of photosynthetic microorganisms evaluated in silico

Harmful microalgal or cyanobacterial blooms result in accumulation of structurally diverse toxins, including cyclic peptides, lactones, and alkaloids, which pose significant risks to aquatic ecosystems and human health. Experimental studies on the enzymatic detoxification of these compounds are limited by their structural complexity and the limited commercial availability of many toxins. In this study, computational molecular docking and molecular dynamics simulations were used to evaluate potential interactions between 31 enzymes and 26 microalgal and cyanobacterial toxins. The affinity, contact surface area, and geometric parameters of the calculated enzyme/toxin models at pH 7.5 and 8.3 were analyzed. Peptide bond-containing toxins and lactone-containing compounds generally exhibited stronger binding and larger contact areas with enzyme active sites than alkaloid toxins. Geometric analysis revealed several enzyme/toxin pairs with catalytically favorable distances and ligand entry angles. Molecular dynamics simulations demonstrated the most stable structural behavior of the Protease A/Cylindrospermopsin complex. Theoretical values of the Michaelis constants for Protease A interacting with the investigated toxins were estimated to range from 44 to 54 μM. Overall, the most appropriate enzyme/toxin interactions were observed for five enzymes: Protease A (with Cylindrospermopsin, Microviridin I), Subtilisin (with Microcystin-LA, Cyanopeptolin 954), Metallo-β-lactamase (with Anatoxin a(S), Azaspiracid), N-acyl homoserine lactonase (with Azaspiracid) and Glutamyl endopeptidase II (with Aeruginosin 298 A). These enzymes were therefore identified as promising candidates for enzymatic detoxification of the toxins produced by corresponding photosynthetic microorganisms. These computational predictions were further supported by in vitro toxicity assays using the bioluminescent bacteria and Nostoc sp. culture broth supernatant treated with a number of selected hydrolytic enzymes. Enzymatic detoxification resulted in up to a 22-fold reduction in toxicity, as determined using bioluminescent bacteria.