Fluorinated amino acids: compatibility with native protein structures and effects on protein–protein interactions

Abstract

Fluorinated analogues of the canonical α-L-amino acids have gained widespread attention as building blocks that may endow peptides and proteins with advantageous biophysical, chemical and biological properties. This critical review covers the literature dealing with investigations of peptides and proteins containing fluorinated analogues of the canonical amino acids published over the course of the past decade including the late nineties. It focuses on side-chain fluorinated amino acids, the carbon backbone of which is identical to their natural analogues. Each class of amino acids--aliphatic, aromatic, charged and polar as well as proline--is presented in a separate section. General effects of fluorine on essential properties such as hydrophobicity, acidity/basicity and conformation of the specific side chains and the impact of these altered properties on stability, folding kinetics and activity of peptides and proteins are discussed (245 references).

Comparison of the structures and stabilities of coiled‐coil proteins containing hexafluoroleucine and t‐butylalanine provides insight into the stabilizing effects of highly fluorinated amino acid side‐chains

“…These values are very similar to those previously calculated for a 4 H, and a 4 F 3 a,which have packing efficiencies of $90% (29). Thus the additional stability imparted by hFLeu does not result from more efficient core packing in a 4 F 3 d and a 4 F 3 (6)(7)(8)(9)(10)(11)(12)(13), that is, fewer void spaces in the core. Instead, it appears better attributed to the increase in the hydrophobic buried surface area due to hFLeu.…”

“…Crystallization of a 4 F 3 d, a 4 F 3 (6-13) and a 4 tbA 6 To investigate how the changes in thermodynamic stability are related to changes in structure we crystallized three of these proteins, a 4 F 3 d, a 4 F 3 (6)(7)(8)(9)(10)(11)(12)(13) and a 4 tbA 6 and determined their structures by Xray crystallography. We were unable to obtain welldiffracting crystals of a 4 F 3 (17)(18)(19)(20)(21)(22)(23)(24), precluding this protein from structural comparison.…”

“…As a nonfluorinated comparison we have determined the structure of a 4 tbA 6 , which contains b-t-butylalanine (tBAla) at all ''a'' and ''d'' positions. This side-chain has a surface area intermediate between that of Leu and hFLeu, so that introducing 24 tBAla residues into the core of a 4 tbA 6 should result in a buried hydrophobic surface area nearly identical to that of either a 4 F 3 d ora 4 F 3 (6)(7)(8)(9)(10)(11)(12)(13). Therefore, any differences in structure and stability are expected to arise primarily from the difference in the shapes of the side-chains.…”

“…a 4 F 3 (6)(7)(8)(9)(10)(11)(12)(13) contains the same number of hFLeu residues as a 4 F 3 a and a 4 F 3 d, but the packing is now altered so that hFleu is introduced at one ''a'' position (10) adjacent to two ''d'' positions (6 and 13); this allows interaction between hFLeu residues on adjacent ''a'' and ''d'' positions to be evaluated. As a nonfluorinated comparison we have determined the structure of a 4 tbA 6 , which contains b-t-butylalanine (tBAla) at all ''a'' and ''d'' positions.…”

“…[8][9][10][11] The substitution of fluorine for hydrogen is generally considered sterically nonperturbing and many ''lightly'' fluorinated amino acids can be processed by endogenous tRNA synthetases. [12][13][14] However, our laboratory and others have focused on introducing highly fluorinated analogs of residues such as valine, leucine, isoleucine, and phenylalanine into proteins as a means of enhancing stability.…”