Effect of Metal Ion and Water Coordination on the Structure of a Gas-Phase Amino Acid

Abstract

The mode of metal ion and water binding to the amino acid valine is investigated using both theory and experiment. Computations indicate that without water, the structure of valine is nonzwitterionic. Both Li(+) and Na(+) are coordinated to the nitrogen and carbonyl oxygen (NO coordination), whereas K(+) coordinates to both oxygens (OO coordination) of nonzwitterionic valine. The addition of a single water molecule does not significantly affect the relative energies calculated for the cationized valine clusters. Experimentally, the rates of water evaporation from clusters of Val.M(+)(H(2)O)(1), M = Li, Na, and K, are measured using blackbody infrared radiative dissociation. The dissociation rate from the valine complex is compared to water evaporation rates from model complexes of known structure. These results indicate that the metal ion in the lithiated and the sodiated clusters is NO-coordinated to nonzwitterionic valine, while that in the potassiated cluster has OO coordination, in full agreement with theory. The zwitterionic vs nonzwitterionic character of valine in the potassiated cluster cannot be distinguished experimentally. Extensive modeling provides strong support for the validity of inferring structural information from the kinetic data.

Hydration of potassiated amino acids in the gas phase

“…Because metal ions and biomolecules are normally surrounded by water in living systems, these interactions are of significant importance in understanding biological systems. Williams and coworkers [8,[25][26][27][28][29][30][31] studied the modes of metal ion and water binding in hydrated complexes of alkali metal cationized valine, glutamine, lysine, and ␣-methyl-proline using both black-␣ ␣ body infrared radiative dissociation (BIRD) experiments and theory. Armentrout et al investigated the sequential bond energies of water to sodiated glycine [32] and proline [33] by threshold collision-induced dissociation (TCID) experiments, as well as by accurate theoretical calculations.…”

“…They play an important role in several biochemical functions such as enzyme regulation, transfer of metal ions from intracellular to extracellular environments, electrical excitability of nerves, stabilization of DNA structures and so on [1]. Therefore, the interaction between alkali metal cations and various amino acids (AAs) has attracted considerable attention, and many experimental and theoretical studies have been conducted [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. These studies show that K ϩ binds to AAs quite differently than Na ϩ .…”

“…These studies show that K ϩ binds to AAs quite differently than Na ϩ . For example, in the case of aliphatic AAs such as glycine (Gly), alanine (Ala), and valine (Val), the Na ϩ ion is coordinated to nitrogen and carbonyl oxygen (NO coordination) in the lowest energy conformers, while K ϩ prefers to bind to the carbonyl and hydroxyl oxygen atoms of the charge-solvated form (OO coordination) [6,8,10,16]. In proline (Pro), phenylalanine (Phe), and cysteine (Cys), the modes of K ϩ binding are similar to those of the corresponding Na ϩ complexes [3-5, 12, 20].…”

Binding energies of water to lithiated valine: Formation of solution-phase structure in vacuo

“…The effects of water on amino acid structure have been investigated using theory [48 -52], spectroscopy [52][53][54][55], and by blackbody infrared radiative dissociation (BIRD) [45,56,57]. Calculations indicate that two water molecules can make the zwitterion form of glycine a local minimum on the potential energy surface, but this structure is still ϳ12 kcal/mol higher in energy than the nonzwitterion [48].…”

“…The structure of cationized valine with different numbers of water molecules attached has been investigated using a combination of BIRD experiments and theory [56,57]. Kinetic data for the loss of a water molecule from cationized valine, Val⅐M ϩ (H 2 O) n , M ϭ Li, Na, K, and related isomers that model the nonzwitterion and zwitterion forms of valine were measured.…”