This is a putative aconitase X swivel domain, which has been predicted by comparative genomic analysis. The domain is mainly found in archaeal and proteobacterial proteins. As such, the prediction should be treated with caution [1]. One member of this entry from Aeropyrum pernix which has been annotated as a putative aconitase, has been characterised in vitro and catalyses the dehydration of mevalonate 5-phosphate to form trans-anhydromevalonate 5-phosphate, a previously unknown intermediate [2], being involved in a "modified" mevalonate pathway.

1: Filling a gap in the central metabolism of archaea: prediction of a novel aconitase by comparative-genomic analysis. Makarova KS, Koonin EV; FEMS Microbiol Lett. 2003;227:17-23. PMID:14568143

2: Modified mevalonate pathway of the archaeon Aeropyrum pernix proceeds via trans-anhydromevalonate 5-phosphate. Hayakawa H, Motoyama K, Sobue F, Ito T, Kawaide H, Yoshimura T, Hemmi H; Proc Natl Acad Sci U S A. 2018;115:10034-10039. PMID:30224495