# The effects of naturally occurring mutations on functionality of oxylipin metabolizing dehydrogenase reductase nine

## TL;DR

This study shows that two mutations in the DHRS9 enzyme, linked to epilepsy, reduce its function, with different effects on protein stability and activity.

## Contribution

The study experimentally characterizes the functional impact of two naturally occurring DHRS9 mutations and reveals structural insights into the enzyme's substrate binding.

## Key findings

- The S202L mutation in DHRS9 causes loss of function due to impaired protein folding or stability.
- The D286H mutation increases the enzyme's Km for NAD+ by 12-fold, reducing catalytic efficiency.
- The 3D structure of DHRS9 reveals a large substrate binding cavity, explaining its ability to process diverse oxylipins.

## Abstract

Recent evidence suggests that dehydrogenase reductase 9 (DHRS9) can oxidize and alter the biological activity of a diverse group of oxylipin substrates, underscoring the importance of DHRS9 in regulating various biological processes, including inflammation, cell proliferation, and tissue repair. Importantly, mutations in the DHRS9 gene resulting in amino acid substitutions S202L and D286H have been linked to an early-onset case of epilepsy; whether these mutations affect the function of DHRS9 has not been investigated. The results of this study demonstrate that both mutations cause a significant loss of DHRS9 functionality. However, in the case of the S202L variant, the loss of catalytic activity likely stems from the impaired protein folding and/or protein stability. On the other hand, the D286H DHRS9 mutant protein is relatively more stable than the S202L variant, but its Km value for NAD+ (2.85 mM) is nearly 12-fold higher than that of the wild-type enzyme. The three-dimensional structure of DHRS9, solved in this study, provides insights into the functions of the S202 and D286 residues. In addition, it reveals a strikingly large substrate binding cavity, consistent with the fact that the enzyme can process oxygenated hydrocarbons with abundant rotational freedom and differing lengths (18–22 C). Considering that expression levels of DHRS9 in human tissues are highly sensitive to inflammatory conditions and the existence of naturally occurring mutations in DHRS9, the structural and functional characterization of DHRS9 reported in this study is critical for a better understanding of the role of DHRS9 in inflammatory processes.