Crystal structure of the human mitochondrial amidoxime-reducing component 1 M187K variant.

Abstract

The human mitochondrial amidoxime-reducing component 1 (mARC1) is a molybdenum-dependent enzyme whose protein-coding variants confer protection against common metabolic liver diseases. Whereas the frequent A165T variant acts largely through accelerated cellular degradation, the basis of protection by the rarer M187K variant remains obscure, as it has been reported that there are no differences between the wild-type and M187K-variant protein in terms of cellular protein levels and localization. Here, the crystal structure of the human mARC1 M187K variant, crystallized as a T4 lysozyme fusion after iterative micro-seeding, was determined at 1.63 Å resolution. The variant structure is essentially superimposable with the previously reported wild-type and A165T structures, with pairwise root-mean-square deviations of 0.3-0.4 Å, and the pentacoordinated molybdenum cofactor is fully intact. Differential scanning fluorimetry across a broad pH range revealed only a modest, pH-dependent decrease in thermal stability associated with the exchange, most pronounced at alkaline pH. These data suggest that the disease-protective effect of M187K is unlikely to originate from gross structural rearrangement or active-site perturbation.

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