ultraviolet and infrared spectroscopy of helical peptides and their water complexes jaime a....
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Ultraviolet and infrared spectroscopy of helical peptides and their water complexes
Jaime A. Stearns, Monia Guidi, Caroline Seaiby, Natalia NagornovaAnnette Svendsen, Oleg V. Boyarkin, and Thomas R. Rizzo
Laboratoire de Chimie Physique MoléculaireEcole Polytechnique Fédérale de Lausanne
April 21, 2023
The Helix
Hudgins, R. R. and M. F. Jarrold (1999). JACS 121: 3494-3501.
(% o
f id
eal h
elix
)
NH
NH
NH
NH
NH
NH
NH
O
O
O O O
O O O
OH
NH3
+
Ac-Phe-(Ala)n-Lys-H+
C13
C10
• What is the detailed structure of the helix?
• How many conformations are there?
• Where do the first water molecules bind?
22-pole ion trap
(6 K)
Experimental setup
UV
S0
S1
fragments
UV Wavenumber / cm-1
Infrared-ultraviolet double resonance spectroscopy
S0
S1
v=1
detectedfragments
UV
IR
fragmentationthreshold
UV only
UV+IR
IR Wavenumber /cm-1
A
B
Ac-Phe-(Ala)5-Lys-H+ UV spectrumFr
agm
enta
tion
yiel
d
3764037620376003758037560375403752037500Wavenumber / cm
-1
A
DC
B
3450340033503300Wavenumber / cm
-1
Frag
men
t dep
letio
n
Phe
Phe
NH stretch spectra of Ac-Phe-(Ala)5-Lys-H+
B3LYP/6-31G** (scaled 0.952)37640376203760037580375603754037520
Wavenumber / cm-1
A B
3 kJ/mol
7 kJ/mol
C10-C10-C13-C13
C10-C10-C10-C10
C10-C13-C13-C13
A
B
0 kJ/mol
Frag
men
t dep
letio
n
3450340033503300Wavenumber / cm
-1
Phe
Phe
37640376203760037580375603754037520Wavenumber / cm
-1
B3LYP/6-31G** (scaled 0.952)
C D
0 kJ/mol
4 kJ/mol
NH stretch spectra of Ac-Phe-(Ala)5-Lys-H+
C10-C10-C10-C10
C10-C13-C13-C13
C10-C10-C10-C13
Low-energy conformations
B3LYP/6-31G**
gauche –(0 kJ/mol)
gauche +(4 kJ/mol)
gauche +(7 kJ/mol)
gauche –(3 kJ/mol)
Where will a water molecule bind?
• Peripheral binding sites: COOH, free NH, system• Integrated binding sites: insertion into C=O•••H-N bonds
We can create Ac-Phe-(Ala)5-Lys-H+•(H2O)n in the ion source, and probe the details of the structure with IR and UV spectroscopy.
Creating water complexes in the ion source
*impurity
Ac-Phe-(Ala)5-Lys-H+•(H2O)n
Ion
inte
nsity
(arb
uni
ts)
1000950900850800750700m/z
*
*
n=1
n=2
n=5
n=10n=16
Ac-Phe-(Ala)5-Lys-H+
m/z 692
n=3 n=4
UV spectra of Ac-Phe-(Ala)5-Lys-H+•(H2O)n Fr
agm
enta
tion
yiel
d
37620376003758037560375403752037500
Wavenumber / cm-1
A B
C Dn=0
n=1
n=2
n=3
n=4
UV spectra of Ac-Phe-(Ala)5-Lys-H+•(H2O)nFr
agm
enta
tion
yiel
d
376503760037550375003745037400Wavenumber / cm
-1
n=4
n=5
n=6
n=8
A
B
Frag
men
tatio
n yi
eld
37003600350034003300Wavenumber / cm
-1
IR spectrum of Ac-Phe-(Ala)5-Lys-H+•(H2O)1
free OH
monomer
v=0
v=1
IR
water complex
Isotopically labeled Ac-Phe-(Ala)5-Lys-H+
15N-Ala anticipated red shift of 8 cm-1
Fra
gmen
t dep
letio
n
350034503400335033003250Wavenumber / cm
-1
all 14
N
15N-Ala
2
15N-Ala
4
15N-Ala
6
Isotopically labeled Ac-Phe-(Ala)5-Lys-H+ monomer
Ala2Ala6Ala4
Frag
men
tatio
n yi
eld
35003450340033503300
Wavenumber / cm-1
all 14
N
15N-Ala
2
15N-Ala
4
15N-Ala
6
AcFA5K-H+-(H2O)1 isotopic substitution
Ala2Ala4Ala4 Ala6
Frag
men
tatio
n yi
eld
3600350034003300Wavenumber / cm
-1
IR spectrum of Ac-Phe-(Ala)5-Lys-H+•(H2O)1
Ac-Phe-(Ala)5-Lys-H+ conf B
Ac-Phe-(Ala)5-Lys-H+ conf C
COOH
bonded H2OAla2
Ala4
Ala6
Ala4
Conclusions
• Ac-Phe-(Ala)5-Lys-H+ is a helical peptide with four conformations at low temperature (10-15 K)
• We can create complexes between this peptide and more than 15 water molecules
• The UV spectra indicate the first four water molecules attach away from the chromophore, likely near the charge
• The fifth water molecule binds near the chromophore
• The first water molecule binds in a double-donor motif
• Both helical backbones are retained upon binding of the first water molecule
Acknowledgements
Prof. Tom Rizzo Monia Guidi Caroline SeaibyDr. Oleg Boyarkin
Dr. Annette Svendsen
Dr. Catherine Servis,Protein and Peptide Chemistry Facility
George PapadopoulosUlrich Lorenz Natalia Nagornova
FNSNFFunding: