Small, but powerful and attractive: 19F in biomolecular NMR

Abstract

Nuclear magnetic resonance (NMR) spectroscopy is a versatile tool for probing structure, dynamics, folding, and interactions at atomic resolution. While naturally occurring magnetically active isotopes, such as ¹H, ¹³C, or ¹⁵N, are most commonly used in biomolecular NMR, with ¹⁵N and ¹³C isotopic labeling routinely employed at the present time, ¹⁹F is a very attractive and sensitive alternative nucleus, which offers rich information on biomolecules in solution and in the solid state. This perspective summarizes the unique benefits of solution and solid-state ¹⁹F NMR spectroscopy for the study of biological systems. Particular focus is on the most recent studies and on future unique and important potential applications of fluorine NMR methodology.

Keywords: NMR; drug discovery; fluorine.

Figure 1.

Superposition of 1D ¹⁹F spectra of 4F-Trp (gray), 5F- (magenta), 6F-Trp (green) and 7F-Trp (blue), and 4F-, 5F-, 6F-, and 7F-Trp121 labeled CypA. Chemical shift differences between the free amino acid and the amino acid when incorporated into the CypA protein are indicated by the dashed arrows. Also depicted are the chemical structure of the Trp amino acid with numbering in the indole ring (top) and a ribbon representation of the CypA structure with an expansion of the active site (right), illustrating the superposition of the differently fluorinated Trp121 side chains. The color coding of the fluorine positions in the structures is identical to that in the spectra.

Figure 2.

The three major methods to prepare ¹⁹F-modified proteins. (Left) covalent conjugation of ¹⁹F-containing moieties to the protein. (Middle) Biosynthetic amino acid type-specific incorporation of ¹⁹F-modified amino acids. (Right) Site-specific incorporation of ¹⁹F-modified amino acids using recombinantly expressed orthogonal amber tRNA/tRNA synthetase pairs.

Figure 3.

Superposition of 1D ¹⁹F spectra of 3F-Tyr labeled α-synuclein in buffer (black dotted line), in cell extract (grey line) and in A2780 cells (black line). Assignments are indicated by residue name and number. A schematic ribbon representation of a single α-synuclein chain with the four Tyr residues shown in stick representation is depicted above the spectra.