Structures of the dedicated futalosine hydrolase and its paralog MTAN from Thermus thermophilus provide insights into enzyme evolution

Abstract:

Menaquinone can be synthesized in bacteria via two different pathways:  the classical pathway that involves products of the men genes [1,2], and the more recently discovered futalosine pathway encoded by mqn genes [3].  The eponymous intermediate futalosine is hydrolyzed to hypoxanthine and dehypoxanthine futalosine (DHFL) by the futalosine hydrolase MqnB, although in some organisms, DHFL is produced directly from the futalosine precursor 6-amino-6-deoxyfutalosine (AFL) by the promiscuous 5’-methylthio adenosine nucleosidase (MTAN) [4,5]. Here we present crystal structures of the Thermus thermophilus enzymes TtMTAN and TtMqnB both in the presence and absence of substrates/analogs and their nucleotide products. We show that although both enzymes undergo significant structural rearrangements upon ligand binding, these occur via very different routes, and demonstrate that nucleoside hydrolysis in the two enzymes proceeds via fundamentally different mechanisms.

 [1] R. Meganathan, O. Kwon, Biosynthesis of Menaquinone (Vitamin K 2 ) and Ubiquinone (Coenzyme Q). EcoSal Plus 3 (2009).

2. M. Kurosu, E. Begari, Vitamin K2 in Electron Transport System: Are Enzymes Involved in Vitamin K2 Biosynthesis Promising Drug Targets? Molecules 15, 1531–1553 (2010).
3. T. Hiratsuka, et al., An Alternative Menaquinone Biosynthetic Pathway Operating in Microorganisms. Science 321, 1670–1673 (2008).
4. S. Wang, et al., A Picomolar Transition State Analogue Inhibitor of MTAN as a Specific Antibiotic for Helicobacter pylori. Biochemistry 51, 6892–6894 (2012).
5. X. Li, D. Apel, E. C. Gaynor, M. E. Tanner, 5′-Methylthioadenosine Nucleosidase Is Implicated in Playing a Key Role in a Modified Futalosine Pathway for Menaquinone Biosynthesis in Campylobacter jejuni. Journal of Biological Chemistry 286, 19392–19398 (2011).