Crystal Structure of an Active Site Mutant Form of IRG1 from Bacillus subtilis

Abstract

Immune-responsive gene1 (IRG1), an enzyme that is overexpressed during immune reactions, catalyzes the production of itaconate from cis-aconitate. Itaconate is a multifunctional immuno-metabolite that displays antibacterial and antiviral activities. The recent resolution of its structure has enabled the mechanism underlying IRG1 function to be speculated on. However, the precise mechanism underlying the enzymatic reaction of IRG1 remains vague owing to the absence of information regarding the structure of the IRG1/substrate or the product complex. In this study, we determined the high-resolution structure of the active site mutant form of IRG1 from Bacillus subtilis (bsIRG1_H102A). Structural analysis detected unidentified electron densities around the active site. Structural comparison with the wildtype revealed that H102 was critical for the precise location of the side chain of residues around active site of IRG1. Finally, the activity of bsIRG1 was extremely low compared with that of mammalian IRG1. The current structural study will expectedly help understand the working mechanism of IRG1.