Cis–Trans Isomerizations of Proline Residues Are Key to Bradykinin Conformations

Abstract

A recent ion mobility – mass spectrometry (IM–MS) study of the nonapeptide bradykinin (BK, amino acid sequence Arg1–Pro2–Pro3–Gly4–Phe5–Ser6–Pro7–Phe8–Arg9) found evidence for 10 populations of conformations that depend upon the solution composition [J. Am. Chem. Soc. 2011, 133, 13810]. Here, the role of the three proline residues (Pro2, Pro3, and Pro7) in establishing these conformations is investigated using a series of seven analogue peptides in which combinations of alanine residues are substituted for prolines. IM–MS distributions of the analogue peptides, when compared to the distribution for bradykinin, indicate the multiple structures are associated with different combinations of cis and trans forms of the three proline residues. These data are used to assign the structures to different peptide populations that are observed under various solution conditions. The assignments also show the connectivity between structures when collisional activation is used to convert one state into another.

Direct Measurement of the Isomerization Barrier of the Isolated Retinal Chromophore

“…Therise of the curve starting at V act = 110 Vp robably corresponds to isomerization into structure X. Interestingly the structure X* is not accessible when starting from structure A. Notably,t he threshold for fragmentation is only slightly larger than that of isomerizing into structure X*. This observation agrees with the proposed gas-phase fragmentation mechanisms [14,15] which involves the formation of ac ompact intermediary structures prior to fragmentation.…”

“…[14][15][16][17] Thes ystem consists of two successive one-meter-long drift tubes followed by at ime-of-flight mass spectrometer.I ons produced by nanospray are accumulated before the entrance of the first drift tube and then pulsed into the drift tube at ar ate of 10 Hz. Within the drift tube,h elium buffer gas is maintained at ap ressure of 3T orr,a nd ac onstant electric field of E = 9.7 Vcm À1 is applied.…”

Photodissociation of Conformer-Selected Ubiquitin Ions Reveals Site-Specific Cis/Trans Isomerization of Proline Peptide Bonds

“…A detailed analysis of different variants of the nonapeptide bradykinin for example revealed that cis/trans isomerization of prolyl-peptide bonds is responsible for the formation of multiple distinct coexisting gasphase conformations. 34 Analysis of a wide number of prolinecontaining peptides furthermore showed that this effect is rather general and not limited to bradykinin. 39 Furthermore, we have recently demonstrated how cis/trans isomerization is influenced by interactions with mono-valent ciations.…”

Structural Resolution of 4-Substituted Proline Diastereomers with Ion Mobility Spectrometry via Alkali Metal Ion Cationization

“…1-2 Also, changes in chirality of single amino acids in the primary sequence of peptides and large proteins can have a significant impact on higher-order structure. [3][4][5][6][7][8] Typically, chiral separations are achieved via liquid or gas chromatography, but optimizations and analysis using these separations can often be long and tedious. [9][10][11] In an effort to eliminate these slow and tedious steps, there has been significant interest in the development of methods that enable chiral discrimination in mass spectrometry (MS).…”