Reconstitution of Vanadium Haloperoxidase's Catalytic Activity by Boric Acid-Towards a Potential Biocatalytic Role of Boron

Boron's unusual properties inspired major advances in chemistry. In Nature, the existence and importance of boron has been fairly explored (e.g. bacterial signaling, plant development) but its role as biological catalyst was never reported. Here, we show that boric acid [B(OH)3] can restore chloroperoxidase activity of Curvularia inaequalis recombinant apo-haloperoxidase's (HPO) in the presence of hydrogen peroxide and chloride ions. Molecular modeling and semi-empirical PM7 calculations support a thermodynamically highly favored (bio)catalytic mechanism similarly to vanadium haloperoxidases (V-HPO) in which [B(OH)3] is assumedly located in apo-HPO's active site and a monoperoxyborate [B(OH)3(OOH)-] intermediate is formed and stabilized by interaction with specific active site amino acids leading ultimately to the formation of HOCl. Thus, B(OH)3-HPO provides the first evidence towards the future exploitation of boron`s role in biological systems.