1. Conformation-specific IR spectroscopy of cold Ac-Phe-(Ala)5-Lys-H+ Ac-Phe-(Ala)10-Lys-H+ Ac-Lys-Phe-(Ala)10-H+ Spectroscopic signatures of helix formation
Jaime A. Stearns, Monia Guidi, Caroline Seaiby, Annette Svendsen,
Oleg V. Boiarkine, and Thomas R. Rizzo
Laboratoire de chimie physique moléculaire
Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland

2. Previous identification of a gas phase helix
Ac-Ala11-Lys-H+
a-helix has 13-membered H-bonding
rings (C13)
310-helix has C10 rings
Hudgins, R. R. and M. F. Jarrold (1999). JACS 121(14):

3. Experimental approach
22-pole ion trap
(6 K) S0 S1
v=1
detected
fragments UV IR

4. Can we spectroscopically identify a helical domain in the gas phase?
Ac-Phe-(Ala)10-Lys-H+ (helical)
Ac-Lys-Phe-(Ala)10-H+ (globular)
Ac-Phe-(Ala)5-Lys-H+
Dissociation time
Spectral complexity
Computational feasibility

5. UV spectra
PheH+
Ac-Phe-(Ala)5-Lys-H+
Ac-Phe-(Ala)10-Lys-H+

6. Ac-Phe-(Ala)5-Lys-H+ OH NH3+ free NH bound NH
go through OH/ less bound NH / bound NH rough, intuitive assignments

7. Ac-Phe-(Ala)5-Lys-H+ 7 kJ/mol A3 A2 A4±A5 K F A1 3 kJ/mol A3 A2 A4±A5OH K F A1
3 kJ/mol
go through specifics of each type of interaction. explain differences A3 A2
A4±A5 F K A1 OH
B3LYP/6-31G** (scaled 0.95)

8. Isotopically labeled Ac-Phe-(Ala)5-Lys-H+
15N-Ala-3
15N-Ala-5 * A5 *
unlabeled A3
unlabeled

9. Ac-Phe-(Ala)10-Lys-H+ A1 A5 A2 (C10) A4 K F A3 (C10) free/ p/ C5OH A2
(C10) A4 K F A3
(C10)
free/ p/ C5

10. Ac-Lys-Phe-(Ala)10-H+ Ac-Phe-(Ala)10-Lys-H+
Hudgins, R. R. and M. F. Jarrold (1999). JACS 121(14):
Ac-Phe-(Ala)10-Lys-H+

11. Ac-Phe-(Ala)5-Lys-H+ C10 free/ p/ C5 Ac-Phe-(Ala)10-Lys-H+ C13 C10OH
C10
free/ p/ C5
Ac-Phe-(Ala)10-Lys-H+
C10
C13
Ac-Lys-Phe-(Ala)10-H+

12. Conclusions
We can use photofragmentation and IR depletion up to a 12-mer
N-H stretches of helical molecules:
free and weakly bound ~ cm-1 (1st two and last residues)
C10 rings ~ 3300 cm-1 (third residue)
C13 a-helical rings ~ cm-1
O-H stretches:
free in helical peptides
hydrogen-bonded in globular peptides
UV spectrum is sensitive to IR absorption 20 Å away

13. Looking Ahead Multiple chromophores to tag different domains
Carbonyl stretches
Water adsorption

14. Protein and Peptide Chemistry Facility
Acknowledgements
Prof. Tom Rizzo
Monia Guidi
Caroline Seaiby
Dr. Catherine Servis,
Protein and Peptide Chemistry Facility
Dr. Oleg Boiarkine
Dr. Annette Svendsen
FNSNF
Funding: