ultraviolet and infrared spectroscopy of helical peptides and their water complexes jaime a....

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: