Heme-thiolate haloperoxidases: versatile biocatalysts with biotechnological and environmental significance

Abstract

Heme-thiolate haloperoxidases are undoubtedly the most versatile biocatalysts of the hemeprotein family and share catalytic properties with at least three further classes of heme-containing oxidoreductases, namely, classic plant and fungal peroxidases, cytochrome P450 monooxygenases, and catalases. For a long time, only one enzyme of this type--the chloroperoxidase (CPO) of the ascomycete Caldariomyces fumago--has been known. The enzyme is commercially available as a fine chemical and catalyzes the unspecific chlorination, bromination, and iodation (but no fluorination) of a variety of electrophilic organic substrates via hypohalous acid as actual halogenating agent. In the absence of halide, CPO resembles cytochrome P450s and epoxidizes and hydroxylates activated substrates such as organic sulfides and olefins; aromatic rings, however, are not susceptible to CPO-catalyzed oxygen-transfer. Recently, a second fungal haloperoxidase of the heme-thiolate type has been discovered in the agaric mushroom Agrocybe aegerita. The UV-Vis adsorption spectrum of the isolated enzyme shows little similarity to that of CPO but is almost identical to a resting-state P450. The Agrocybe aegerita peroxidase (AaP) has strong brominating as well as weak chlorinating and iodating activities, and catalyzes both benzylic and aromatic hydroxylations (e.g., of toluene and naphthalene). AaP and related fungal peroxidases could become promising biocatalysts in biotechnological applications because they seemingly fill the gap between CPO and P450 enzymes and act as "self-sufficient" peroxygenases. From the environmental point of view, the existence of a halogenating mushroom enzyme is interesting because it could be linked to the multitude of halogenated compounds known from these organisms.

Pyridine as novel substrate for regioselective oxygenation with aromatic peroxygenase from Agrocybe aegerita

“…AaP (AaP; also referred to as haloperoxidase or haloperoxidase-peroxygenase and nowadays named aromatic peroxygenase) [16][17][18][19]22] was purified by several steps of ion exchange chromatography as described previously [21]. The final AaP preparation (isoform AaP II) used in the present study had a specific activity of 75 Units per mg protein (U mg À1 , substrate veratryl alcohol) and an RZ 420/280 value of 1.7; its physico-chemical properties are described elsewhere [16,[21][22][23].…”

“…The final AaP preparation (isoform AaP II) used in the present study had a specific activity of 75 Units per mg protein (U mg À1 , substrate veratryl alcohol) and an RZ 420/280 value of 1.7; its physico-chemical properties are described elsewhere [16,[21][22][23].…”

Chlorination of lignin by ubiquitous fungi has a likely role in global organochlorine production

“…A variety of plant pathogenic ascomycetes that also occur as litter saprophytes have been reported to secrete chloroperoxidases (CPOs) on defined culture media (9,10), and uncharacterized CPO activity has also been detected in soils (11), which generally contain significant fungal biomass (12). Fungal CPOs are hemeor vanadium-containing enzymes that catalyze the H 2 O 2 -dependent oxidation of Cl Ϫ to hypochlorous acid (HOCl) or a similarly reactive chlorine electrophile, and as a result they chlorinate lignin and related aromatic structures in vitro (13-16).…”

Characterization of Recombinant Chloroperoxidase, and F103A and C29H/C79H/C87H Mutants

“…In addition to peroxide dependent halogenations (Thomas and Hager 1968;, CPO is also able to catalyze a broad spectrum of reactions Hofrichter and Ullrich 2006), including the typical peroxidase reactions, catalase reactions , some P450-like oxidation reactions (Hollenberg and Hager 1973), as outlined in scheme 1. In addition, CPO has the potential to catalyze the synthesis of a wide range of chiral or prochiral products.…”