Sulfhydryl oxidases: sources, properties, production and applications

Abstract

The formation of disulfide bonds in proteins and small molecules can greatly affect their functionality. Sulfhydryl oxidases (SOXs) are enzymes capable of oxidising the free sulfhydryl groups in proteins and thiol-containing small molecules by using molecular oxygen as an electron acceptor. SOXs have been isolated from the intracellular compartments of many organisms, but also secreted SOXs are known. These latter enzymes are generally active on small compounds and their physiological role is unknown, whereas the intracellular enzymes prefer proteins as substrates and are involved in protein folding. An increasing number of scientific publications and patent applications on SOXs have been published in recent years. The present mini-review provides an up-to-date summary of SOXs from various families, their production and their actual or suggested applications. The sequence features and domain organisation of the characterised SOXs are reviewed, and special attention is paid to the physicochemical features of the enzymes. A review of patents and patent applications regarding this class of enzymes is also provided.

Enzyme-catalyzed protein crosslinking

“…In this article, we focus on oxidoreductases that have been experimentally shown to catalyze redox reactions directly at functional amino acid side chains of target proteins. Hence, we do not include glucose oxidases (Wong et al 2008) and sulfhydryl oxidases (Faccio et al 2011) that are proposed to induce intermolecular crosslinking of food proteins mainly by producing reactive hydrogen peroxide from small-molecule sugars and thiols, respectively.…”

Exploring the Smallest Active Fragment of HsQSOX1b and Finding a Highly Efficient Oxidative Engine

“…QSOXs belong to a group of enzymes called sulfhydryl oxidases, which includes the flavin adenine dinucleotide (FAD) prosthetic group, and oxidize small molecular thiol-containing substrate, i.g. dithiothreitol (DTT) and glutathione (GSH) [1], [11]. Among these enzymes, only QSOXs are capable of the facile and direct insertion of disulfide bonds into reduced client proteins, which is termed protein thiol oxidase activity.…”

Enzymatic modification of dairy product texture

“…The substrate specificity of SOXs is not strict and ranges from small thiol compounds such as DTT to protein-bound cysteine residues (Faccio et al, 2011). Molecular oxygen is reduced either to hydrogen peroxide or water, depending on the structure and the origin of the SOX.…”

“…Molecular oxygen is reduced either to hydrogen peroxide or water, depending on the structure and the origin of the SOX. Fungal SOXs have shown positive effects on dough characteristics when used together with glucose oxidase or hemicellulases (see review by Faccio et al, 2011) or in presence of ascorbic acid (Faccio et al, 2012a). SOXs naturally exist in bovine milk.…”