This domain is found in 1-Cys type selenoprotein methionine sulfoxide reductase A (MsrA) from the bacteria Clostridium oremlandii, a repair enzyme for proteins that have been inactivated by oxidation that is found both in prokaryotes and eukaryotes. MsrA catalyses the reduction of methionine sulfoxide in proteins to methionine. This enzyme is organised into a catalytic domain (Pfam:PF01625) and a helical domain (this entry) absent in most of the known MsrA structures. It consists of five helices, interacts with the catalytic domain and is essential for the active site formation [1,2].

1: Structural analysis of 1-Cys type selenoprotein methionine sulfoxide reductase A. Lee EH, Kwak GH, Kim MJ, Kim HY, Hwang KY; Arch Biochem Biophys. 2014;545:1-8. PMID:24412203

2: Evidence for the dimerization-mediated catalysis of methionine sulfoxide reductase A from Clostridium oremlandii. Lee EH, Lee K, Kwak GH, Park YS, Lee KJ, Hwang KY, Kim HY; PLoS One. 2015;10:e0131523. PMID:26107511