Enantioselective Collision-Activated Dissociation of Gas-Phase Tryptophan Induced by Chiral Recognition of Protonated L-Alanine Peptides.

Abstract

Listen

Translate article

Enantioselective dissociation in the gas phase is important for enantiomeric enrichment and chiral transmission processes in molecular clouds regarding the origin of homochirality in biomolecules. Enantioselective collision-activated dissociation (CAD) of tryptophan (Trp) and the chiral recognition ability of L-alanine peptides (L-Ala n ; n=2-4) were examined using a linear ion trap mass spectrometer. CAD spectra of gas-phase heterochiral H+(D-Trp)(L-Ala n ) and homochiral H+(L-Trp)(L-Ala n ) noncovalent complexes were obtained as a function of the peptide size n. The H2O-elimination product was observed in CAD spectra of both heterochiral and homochiral complexes for n=2 and 4, and in homochiral H+(L-Trp)(L-Ala3), indicating that the proton is attached to the L-alanine peptide, and H2O loss occurs from H+(L-Ala n ) in the noncovalent complexes. H2O loss did not occur in heterochiral H+(D-Trp)(L-Ala3), where NH3 loss and (H2O+CO) loss were the primary dissociation pathways. In heterochiral H+(D-Trp)(L-Ala3), the protonation site is the amino group of D-Trp, and NH3 loss and (H2O+CO) loss occur from H+(D-Trp). L-Ala peptides recognize D-Trp through protonation of the amino group for peptide size n=3. NH3 loss and (H2O+CO) loss from H+(D-Trp) proceeds via enantioselective CAD in gas-phase heterochiral H+(D-Trp)(L-Ala3) at room temperature, whereas L-Trp dissociation was not observed in homochiral H+(L-Trp)(L-Ala3). These results suggest that enantioselective dissociation induced by chiral recognition of L-Ala peptides through protonation could play an important role in enantiomeric enrichment and chiral transmission processes of amino acids.