Crystal Structure of the Active Site Mutant Form of Soluble Fumarate Reductase, Osm1

Kim Kim,Jung Jung,Chun Chun,Ha Ha,Park Park,Kwon Kwon

doi:10.3390/cryst9100504

Abstract

Soluble fumarate reductase is essential for survival under anaerobic conditions. This enzyme can maintain the redox balance in the cell by catalyzing the reduction of fumarate to succinate. Although the overall reaction mechanism of soluble fumarate reductase in yeast, Osm1, has been proposed by a previous structural study, the details of the underlying mechanism are not completely elucidated. The present study provides the structural information regarding the active site mutant form of Osm1 (R326A), thus, revealing that R326A mutation does not affect the substrate binding. Structural alterations of the residues surrounding the active site, and the missing 2nd flavin adenine dinucleotide (FAD) in the previously defined 2nd FAD binding site, were observed as characteristic features of the Osm1 R326A crystal structure. Based on these findings, we provided a clue that can explain the loss of activity of Osm1 R326A.

Highlights

Fumarate reductase is an enzyme that can reduce fumarate to succinate using flavin adenine dinucleotide (FAD) as a cofactor [1,2]
Unlike bacterial soluble fumarate reductase that contains three functional domains, the eukaryotic soluble fumarate reductase in yeast (Osm1) is organized into two distinct domains, the flavin domain, which contains the noncovalently bound FAD as a cofactor, and the clamp domain, which is believed to be involved in controlling substrate access to the active site (Figure 1a)
Previous enzymatic studies revealed that six residues around the active site, namely, H281, E301, R304, R326, H435, and R477, are crucial for the activity of Osm1 [12]

Summary

Introduction

Fumarate reductase is an enzyme that can reduce fumarate to succinate using flavin adenine dinucleotide (FAD) as a cofactor [1,2]. This enzyme is important for maintaining the redox balance in the cell during an oxygen deficient state, and is crucial in cell survival under anaerobic conditions [3]. The clear differences between these two classes indicate that the membrane-bound form of fumarate reductase contains a covalently bound FAD cofactor, with a high redox potential, which catalyzes a reversible reaction. The soluble form contains noncovalently bound FAD, with a low redox potential, which catalyzes an irreversible reaction [4,5].

Methods

Results

Conclusion