RESEARCH ARTICLE


Biochemical Characterization of Two Clinically-Relevant Human Fumarase Variants Defective for Oligomerization



Artemisa Bulku1, #, Todd M. Weaver2, Melanie B. Berkmen1, *
1 Department of Chemistry and Biochemistry, Suffolk University, 8 Ashburton Place, Boston, MA, USA
2 Department of Chemistry and Biochemistry, University of Wisconsin-La Crosse, La Crosse, WI, USA


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© 2018 Bulku et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Department of Chemistry and Biochemistry, Suffolk University, 8 Ashburton Place, Boston, USA; Tel: +1-617-973-5321; Fax: +1-617-573-8668; Email: mberkmen@suffolk.edu

# Novartis Institutes for BioMedical Research, Inc., Cambridge, MA, USA


Abstract

Background:

Fumarase, a significant enzyme of energy metabolism, catalyzes the reversible hydration of fumarate to L-malate. Mutations in the FH gene, encoding human fumarase, are associated with fumarate hydratase deficiency (FHD) and hereditary leiomyomatosis and renal cell cancer (HLRCC). Fumarase assembles into a homotetramer, with four active sites. Interestingly, residues from three of the four subunits within the homotetramer comprise each active site. Hence, any mutation affecting oligomerization is predicted to disrupt enzyme activity.

Methods:

We constructed two variants of hexahistidine-tagged human recombinant fumarase, A308T and H318Y, associated with FHD and HLRCC, respectively. Both Ala308 and His318 lie within the fumarase intersubunit interface. We purified unmodified human fumarase and the two variants, and analyzed their enzymatic activities and oligomerization states in vitro.

Results:

Both variants showed severely diminished fumarase activity. Steady-state kinetic analysis demonstrated that the variants were largely defective due to decreased turnover rate, while displaying Km values for L-malate similar to unmodified human recombinant fumarase. Blue native polyacrylamide gel electrophoresis and gel filtration experiments revealed that each variant had an altered oligomerization state, largely forming homodimers rather than homotetramers.

Conclusion:

We conclude that A308T and H318Y render human fumarase enzymatically inactive via defective oligomerization. Therefore, some forms of FHD and HLRCC can be linked to improperly folded quaternary structure.

Keywords: Fumarase, Fumarate hydratase, Fumarate hydratase deficiency, Fumaric aciduria, Hereditary leiomyomatosis, Renal cell cancer.