Diversification of Quiescin sulfhydryl oxidase in a preserved framework for redox relay

Abstract

BackgroundThe enzyme family Quiescin Sulfhydryl Oxidase (QSOX) is defined by the presence of an amino-terminal thioredoxin-fold (Trx) domain and a carboxy-terminal Erv family sulfhydryl oxidase domain. QSOX enzymes, which generate disulfide bonds and transfer them to substrate proteins, are present in a wide variety of eukaryotic species including metazoans and plants, but are absent from fungi. Plant and animal QSOXs differ in their active-site amino acid sequences and content of non-catalytic domains. The question arises, therefore, whether the Trx-Erv fusion has the same mechanistic significance in all QSOX enzymes, and whether shared features distinguish the functional domains of QSOX from other instances in which these domains occur independently. Through a study of QSOX phylogeny and an analysis of QSOX sequence diversity in light of recently determined three-dimensional structures, we sought insight into the origin and evolution of this multi-domain redox alliance.ResultsAn updated collection of QSOX enzymes was used to confirm and refine the differences in domain composition and active-site sequence motif patterns of QSOXs belonging to various eukaryotic phyla. Beyond the expected phylogenetic distinction of animal and plant QSOX enzymes, trees based on individual redox-active QSOX domains show a particular distinction of the Trx domain early in plant evolution. A comparison of QSOX domains with Trx and Erv domains from outside the QSOX family revealed several sequence and structural features that clearly differentiate QSOXs from other enzymes containing either of these domains. Notably, these features, present in QSOXs of various phyla, localize to the interface between the Trx and Erv domains observed in structures of QSOX that model interdomain redox communication.ConclusionsThe infrastructure for interdomain electron relay, previously identified for animal and parasite QSOXs, is found broadly across the QSOX family, including the plant enzymes. We conclude that the conserved three-dimensional framework of the QSOX catalytic domains accommodates lineage-specific differences and paralog diversification in the amino acid residues surrounding the redox-active cysteines. Our findings indicate that QSOX enzymes are characterized not just by the presence of the two defining domain folds but also by features that promote coordinated activity.

Going through the Barrier

“…It should be noted that there is an additional CXXC motif toward the C terminus of the ERV domain. Although this C V XXC VI motif is conserved in all QSOX sequences examined to date (1,19), single or double mutations at this locus have an insignificant impact on the turnover of protein substrates in vitro using either human QSOX1 or TbQSOX (28,32). Furthermore, the recent crystal structures of open and closed forms of TbQSOX (Fig.…”

“…TbQSOX proves especially tractable to express in Escherichia coli (28), and its three-domain structure represents the minimal architecture for this family of multidomain sulfhydryl oxidases (16,19,28,29). Fig.…”

Characterization of a Sulfhydryl Oxidase From Plasmodium berghei as a Target for Blocking Parasite Transmission

“…Analogously, QSOX enzymes have been found in secreted fluids including milk, semen, egg white and blood serum (Hoober et al, 1996 ; Benayoun et al, 2001 ; Zanata et al, 2005 ; Jaje et al, 2007 ). The extracellular QSOXs in different biological systems suggest they may play diverse roles (Limor-Waisberg et al, 2013 ). For instance, it was found that extracellular catalysis of disulfide bond formation by human QSOX1 is needed for laminin incorporation into the extracellular matrix, which is a prerequisite for tumor adhesion and metastasis (Ilani et al, 2013 ).…”

“…Quiescin sulfhydryl oxidase (QSOX) family enzymes, found in eukaryotes except fungi, specifically catalyze the direct and facile introduction of disulfide bonds into unfolded, reduced proteins with the reduction of a molecular oxygen, generating hydrogen peroxide: 2RSH+O 2 → RS-SR+H 2 O 2 (Haque et al, 2012 ; Limor-Waisberg et al, 2013 ). Two moieties of the enzyme carry out the tandem actions of substrate oxidation and electron transfer: thioredoxin-fold (Trx) domain and a sulfhydral oxidase module related to the Erv/ALR enzyme family.…”

“…A helix-rich region between the Trx and Erv/ALR domains adopts a structural fold similar to the Erv domain, and is thus known as the pseudo-Erv domain (ψErv) (Alon et al, 2010 ). Interestingly, metazoan QSOX enzymes have a second Trx-fold domain (Trx-2) between the active Trx domain and the ψErv domain, whereas this Trx-2 domain is absent in plant and protist QSOXs (Kodali and Thorpe, 2010 ; Haque et al, 2012 ; Limor-Waisberg et al, 2013 ). While the functional significance of QSOXs has been increasingly appreciated, recent studies have revealed that elevated human QSOX is strongly correlated with certain diseases including pancreatic cancer (Katchman et al, 2011 ), heart failure (Mebazaa et al, 2012 ), breast cancer (Soloviev et al, 2013 ; Poillet et al, 2014 ), and prostate tumorigenesis (Song et al, 2009 ).…”