Conformation-specific IR spectroscopy of cold Ac-Phe-(Ala)5-Lys-H+ Ac-Phe-(Ala)10-Lys-H+ Ac-Lys-Phe-(Ala)10-H+
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 molculaire Ecole Polytechnique Fdrale de Lausanne (EPFL), Lausanne, Switzerland Previous identification of a gas phase helix Ac-Ala11-Lys-H+ -helix has 13-membered H-bonding rings (C13) 310-helix has C10 rings Hudgins, R. R. and M. F. Jarrold (1999). JACS 121(14): 3494-3501. Experimental approach 22-pole ion trap (6 K) S1 detected fragments UV v=1 IR S0 Can we spectroscopically identify a helical domain in the gas phase?
+ NH3 Ac-Phe-(Ala)10-Lys-H+ (helical) O H N N H O O H N N H O O H N N H O O
H N N H O O H N N H O O H N OH N H O O Ac-Lys-Phe-(Ala)10-H+ (globular) +
NH3 O N H H N O O N H H N O O N H H N O O N H O H N N
H O O H N N H O O H N OH O Ac-Phe-(Ala)5-Lys-H+ Dissociation time Spectral complexity Computational feasibility H N O O N H
H N O O N H H N O O N H H N O OH O + NH3 UV spectra PheH+ Fragmentation yield Ac-Phe-(Ala)5-Lys-H+ Ac-Phe-(Ala)10-Lys-H+
37500 37520 37540 37560 37580 -1 Wavenumber / cm 37600 37620 37640 Fragment depletion Ac-Phe-(Ala)5-Lys-H+ OH NH3+ 3200 bound NH 3300 free NH 3400 -1 Wavenumber / cm 37520
3500 37540 37560 37580 -1 Wavenumber / cm 3600 37600 37620 37640 Ac-Phe-(Ala)5-Lys-H+ 7 kJ/mol A3 Fragment depletion A2 A4A5 OH K F A1 3 kJ/mol A2
3300 A3 A4A5 3350 F K OH A1 3400 3450 -1 Wavenumber / cm 3500 3550 3600 B3LYP/6-31G** (scaled 0.95) Fragment depletion Isotopically labeled Ac-Phe-(Ala)5-Lys-H+ N-Ala-3 N-Ala-5
37520 Ac-Phe-(Ala)10-Lys-H+ 37560 37600 -1 Wavenumber / cm 37640 Ac-Phe-(Ala)5-Lys-H+ Fragment depletion A2 (C10) 3250 3300 A5 A3 (C10) 3350 A4 F K A1
OH free/ / C5 3400 3450 -1 Wavenumber / cm 3500 3550 3600 Hudgins, R. R. and M. F. Jarrold (1999). JACS 121(14): 3494-3501. Relative fragmentation Ac-Lys-Phe-(Ala)10-H+ Ac-Phe-(Ala)10-Lys-H+ 37500 37520 37540 37560 -1 Wavenumber / cm 37580 37600
Ac-Phe-(Ala)5-Lys-H+ OH Fragment depletion C10 C10 C13 free/ / C5 Ac-Phe-(Ala)10-Lys-H+ Ac-Lys-Phe-(Ala)10-H+ 3200 3300 3400 -1 Wavenumber / cm 3500 3600 Conclusions We can use photofragmentation and IR depletion up to a 12-mer N-H stretches of helical molecules: free and weakly bound ~3400-3500 cm-1 (1st two and last residues) C10 rings ~ 3300 cm-1 (third residue) C13 -helical rings ~3320-3370 cm-1 O-H stretches: free in helical peptides
hydrogen-bonded in globular peptides UV spectrum is sensitive to IR absorption 20 away Looking Ahead Multiple chromophores to tag different domains Carbonyl stretches Water adsorption Acknowledgements Prof. Tom Rizzo Monia Guidi Caroline Seaiby Dr. Catherine Servis, Protein and Peptide Chemistry Facility Dr. Oleg Boiarkine Funding: Dr. Annette Svendsen FN SNF
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