# Molecular basis of hyper-thermostability in the thermophilic archaeal aldolase MfnB

## TL;DR

This study investigates how a specific enzyme from a heat-loving archaea becomes stable at high temperatures, revealing structural adaptations that help it withstand heat.

## Contribution

The paper identifies structural features in the MfnB enzyme from Methanocaldococcus jannaschii that contribute to its hyper-thermostability.

## Key findings

- The MfnB enzyme from Methanocaldococcus jannaschii shows greater thermal stability compared to its mesophilic counterpart.
- Molecular dynamics simulations reveal more side chain interactions in the hyperthermophile enzyme, contributing to its heat resistance.
- Thermal unfolding and kinetic studies confirm the thermoadaptation of the M. jannaschii MfnB enzyme.

## Abstract

Methanogenic archaea are chemolithotrophic prokaryotes that can reduce carbon dioxide with hydrogen gas to form methane. These microorganisms make a significant contribution to the global carbon cycle, with methanogenic archaea from anoxic environments estimated to contribute > 500 million tons of global methane annually. Archaeal methanogenesis is dependent on the methanofurans; aminomethylfuran containing coenzymes that act as the primary C1 acceptor molecule during carbon dioxide fixation. Although the biosynthetic pathway to the methanofurans has been elucidated, structural adaptations which confer thermotolerance to Mfn enzymes from extremophilic archaea are yet to be investigated. Here we focus on the methanofuran biosynthetic enzyme MfnB, which catalyses the condensation of two molecules of glyceralde-3-phosphate to form 4‑(hydroxymethyl)-2-furancarboxaldehyde-phosphate. In this study, MfnB enzymes from the hyperthermophile Methanocaldococcus jannaschii and the mesophile Methanococcus maripaludis have been recombinantly overexpressed and purified to homogeneity. Thermal unfolding studies, together with steady-state kinetic assays, demonstrate thermoadaptation in the M. jannaschii enzyme. Molecular dynamics simulations have been used to provide a structural explanation for the observed properties. These reveal a greater number of side chain interactions in the M. jannaschii enzyme, which may confer protection from heating effects by enforcing spatial residue constraints.

The online version contains supplementary material available at 10.1007/s00792-024-01359-x.