A complete nicotinate degradation pathway in the microbial eukaryote Aspergillus nidulans

Abstract

Several strikingly different aerobic and anaerobic pathways of nicotinate breakdown are extant in bacteria. Here, through reverse genetics and analytical techniques we elucidated in Aspergillus nidulans, a complete eukaryotic nicotinate utilization pathway. The pathway extant in this fungus and other ascomycetes, is quite different from bacterial ones. All intermediate metabolites were identified. The cognate proteins, encoded by eleven genes (hxn) mapping in three clusters are co-regulated by a specific transcription factor. Several enzymatic steps have no prokaryotic equivalent and two metabolites, 3-hydroxypiperidine-2,6-dione and 5,6-dihydroxypiperidine-2-one, have not been identified previously in any organism, the latter being a novel chemical compound. Hydrolytic ring opening results in α-hydroxyglutaramate, a compound not detected in analogous prokaryotic pathways. Our earlier phylogenetic analysis of Hxn proteins together with this complete biochemical pathway illustrates convergent evolution of catabolic pathways between fungi and bacteria.

Synthesis and crystallographic characterization of 6-hydroxy-1,2-dihydropyridin-2-one

“…6-Hydroxy-1,2-dihydropyridin-2-one, more commonly known as 2,6-dihydroxypyridine (2,6-DHP), is a derivative of nicotinic acid, a common compound found within personal care products (Behrman & Stanier, 1957;Hicks et al, 2016;Nakamoto et al, 2019). Recent work has focused on the bacterial hydrolysis of nicotinic acid for use in bioremediation efforts (Bokor et al, 2022). Synthesis of 2,6-DHP can be accomplished by reaction between 2,6-dichloropyridine and potassium tert-butoxide to afford 2,6-di-tert-butoxypyridine (1) followed by reaction with formic acid to produce the product 2 as the pyridone tautomer (Scheme 1; Kocienski, 1994).…”