Crystal structure and mechanism of a bacterial fluorinating enzyme

Abstract

Fluorine is the thirteenth most abundant element in the earth's crust, but fluoride concentrations in surface water are low and fluorinated metabolites are extremely rare. The fluoride ion is a potent nucleophile in its desolvated state, but is tightly hydrated in water and effectively inert. Low availability and a lack of chemical reactivity have largely excluded fluoride from biochemistry: in particular, fluorine's high redox potential precludes the haloperoxidase-type mechanism used in the metabolic incorporation of chloride and bromide ions. But fluorinated chemicals are growing in industrial importance, with applications in pharmaceuticals, agrochemicals and materials products. Reactive fluorination reagents requiring specialist process technologies are needed in industry and, although biological catalysts for these processes are highly sought after, only one enzyme that can convert fluoride to organic fluorine has been described. Streptomyces cattleya can form carbon-fluorine bonds and must therefore have evolved an enzyme able to overcome the chemical challenges of using aqueous fluoride. Here we report the sequence and three-dimensional structure of the first native fluorination enzyme, 5'-fluoro-5'-deoxyadenosine synthase, from this organism. Both substrate and products have been observed bound to the enzyme, enabling us to propose a nucleophilic substitution mechanism for this biological fluorination reaction.

PRODRG: a tool for high-throughput crystallography of protein–ligand complexes

“…Ekstrom et al, 2002;Evans et al, 2002;Gadola et al, 2002;Hall et al, 2002;Matern et al, 2003;Nicolet et al, 2003;Zavala-Ruiz et al, 2003;Dong et al, 2004).…”

Perfluorocarbons: Life sciences and biomedical uses Dedicated to the memory of Professor Guy Ourisson, a true RENAISSANCE man.

“…Enzymatic processes exist that form and break the CÀ ÀF bonds present in these compounds. 13 On the other hand, no natural perfluorocompounds or moieties have, as yet, been found. Consequently, nature did not bother to develop the enzymatic machinery that would allow for their generation and recycling.…”

The Fluorinase from Streptomyces cattleya Is Also a Chlorinase

“…A stereochemical study that involved (5′S)-[5′-2 H]-SAM has indicated that the C-F bond of 5′-FDA replaces the C-S bond of SAM with an inversion of configuration. [11,12] This observation, as well as a theoretical study [13] and structural analysis [10] all suggest an S N 2 reaction mechanism for the fluorinase. Despite the high bonddissociation energy of the C-F bond (the strongest bond in organic chemistry [14] ), we herein report that the fluorinase operates in the reverse direction and that it utilizes a chloride ion.…”

“…[3][4][5] After depurination, 5′-FDA is metabolized first to 5-fluoro-5-deoxyribose-1-phosphate (5′-FRP) [6] and then to fluorocetaldehyde. [7] Fluoroacetaldehyde is converted separately into fluoroacetate [8] and 4-fluorothreonine [9] (Scheme 1).The fluorination enzyme, which has been the subject of a recent structural study, [10] has been isolated and fully characterized, the gene has been cloned, and the enzyme has been overexpressed. A stereochemical study that involved (5′S)-[5′-2 H]-SAM has indicated that the C-F bond of 5′-FDA replaces the C-S bond of SAM with an inversion of configuration.…”

“…The fluorination enzyme, which has been the subject of a recent structural study, [10] has been isolated and fully characterized, the gene has been cloned, and the enzyme has been overexpressed. A stereochemical study that involved (5′S)-[5′-2 H]-SAM has indicated that the C-F bond of 5′-FDA replaces the C-S bond of SAM with an inversion of configuration.…”