Relationship between the angular characteristics of a hydrogen bond and the energetics of proton transfer occurring within

Conformations of protonated gas-phase bradykinin ions: evidence for intramolecular hydrogen bonding

The post-source decay of bradykinin, Lys1-bradykinin, des-Arg1-bradykinin, des-Arg9-bradykinin and [D-Phe7]-bradykinin [M + H]+ ions was examined in order to assertain the influence of secondary structure on peptide ion dissociation. Fragment ions corresponding to the elimination of H2O and HN=C=NH are observed in the product ion mass spectra of Lys1-bradykinin and des-Arg1-bradykinin but not in the spectra of bradykinin or des-Arg9-bradykinin. Cleavage reactions at the Phe-Ser and/or Ser-Pro bonds are observed for all peptide [M + H]+ ions with the exception of des-Arg9-bradykinin. The product ions arising from the processes described above are rationalized in terms of the intramolecular solvation of the protonated guanidino groups of the arginines. The strongest intramolecular interaction appears to be a proton bridge between the guanidino groups of the N- and C-terminal arginines in bradykinin. In addition, increased abundances of fragment ions in the vicinity of Ser-Pro may be attributed to intramolecular solvation of the protonated C-terminal guanidino group by the Ser-Pro portion of the molecule. This self-solvation of the ionizing proton leads to a gas-phase peptide conformation that is supported by solution-phase NMR studies at elevated temperatures and in non-polar solvents but which is different from the conformation in polar solvents.

Internal water molecules and H-bonding in biological macromolecules: a review of structural features with functional implications

Conserved structural patterns of internal water molecules and/or H-bond chains were observed and are here correlated in this review, which then describes two functional properties: equilibration of hydrostatic pressure and proton transport. Available evidence in support of these hypotheses is presented, together with suggested experiments to test them. High-resolution crystal structures of a variety of proteins were studied with interactive computer graphics. Conserved H-bonding linkages may be used as a paradigm for a rationalization of proton transport in membranes. The concept of the "proton wire," which links buried active-site amino acids with the surface of the protein raises the more general question of the functional role of the various molecular components.