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Updated: Jun 15, 2026

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QSOX contains a pseudo-dimer of functional and degenerate sulfhydryl oxidase domains
Assaf Alon1, Erin J Heckler, Colin Thorpe
1Department of Structural Biology, Weizmann Institute of Science, Rehovot, Israel.
Abstract:
Quiescin sulfhydryl oxidase (QSOX) catalyzes formation of disulfide bonds between cysteine residues in substrate proteins. Human QSOX1 is a multi-domain, monomeric enzyme containing a module related to the single-domain sulfhydryl oxidases of the Erv family. A partial QSOX1 crystal structure reveals a single-chain pseudo-dimer mimicking the quaternary structure of Erv enzymes. However, one pseudo-dimer "subunit" has lost its cofactor and catalytic activity. In QSOX evolution, a further concatenation to a member of the protein disulfide isomerase family resulted in an enzyme capable of both disulfide formation and efficient transfer to substrate proteins.
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