hydration of small peptides - uc santa barbara

Hydration of Small Peptides

Thomas Wyttenbach, Dengfeng Liu,and Michael T. Bowers

http://bowers.chem.ucsb.edu/

Why study hydration?Is a certain property of a molecule

(e.g. conformation)inherent to the molecule

or a consequence of solute–solvent interaction?

water(theory)3

apolar solvent(NMR)1

water:2

• no NMR structure• no α-helix• no β-sheet• hydrophobic core

1 Crescenzi et al Eur J Biochem 269, 5642 (2002)

2 Zhang et alJ Struct Biology 130, 130 (2000)

3 Baumketner, SheaUCSB, unpublished

Alzheimer amyloid β-peptide

gasphase

(theory)3

Why study hydration?

Bridge gas phase and solution phase

Study effect of individual water molecules on solute molecules

• energetics (water binding energy)

• structureconformations, foldingzwitterion formationhydration sites

Myoglobin

NMR structure

Mass SpectraNeurotensin

2 torr H2O286 K

(M+2H)2+

(M+3H)3+

(M+H)+

1 H2O(ELYENKPRRPYIL)

ESI IonSource

IonFunnel

DriftCell

DriftCell MSMS DetectorDetector

Instrumentation

M+ M+•(H2O)n

~1 torr H2O

Liquid N2 cooling

Electricalheaters

2 torr H2O286 K

(M+2H)2+

(M+3H)3+

(M+H)+

M+ M+•(H2O)n

~1 torr H2Om/z

1800 µs

900 µs

2700 µs

drift time

Neurotensin (M+2H)2+

290 K, 1.8 torr H2O

Equilibrium?YES

2 torr H2O286 K

(M+2H)2+

(M+3H)3+

(M+H)+

M+ M+•(H2O)n

~1 torr H2O

Equilibrium?

ratio ofpeak intensities

equilibriumconstant

van’t Hoff

∆H° and ∆S°

Data Analysis

∆H° ∆S°+

⊕ ⊕

• Amine

• Guanidine

• Imidazole

• Carboxylate

lysN-terminus

aspgluC-terminus

In peptides and proteins they are:

Charged groups are important.

Ionic Groups The Ammonium GroupThe Guanidinium GroupThe Carboxylate Group

Several Ionic GroupsMultiply Charged IonsSalt Bridges

Challenges AheadChange of ConformationZwitterion Formation

Entropy

CH3NH3+

B3LYP/6-311++G**

secondsolvation

1 2 3 4 56

18 Experiment MM DFT

Number of water molecules

n-decylamine

Experiment

second solvation shell

MolecularMechanicsAMBER, TIP3P

first solvation shell

Ionic hydrogen bond:

electrostatic interaction important

⊕⊕

17kcal/molexperiment1

& DFT2

15 kcal/molexperiment2

1 Meot-NerJACS 1984, 106, 1265

2 Liu, Wyttenbach, Barran, Bowers,JACS 2003, 125, 8458

M+•(H2O)n

103122151

∆H°kcal/mol

0.100.903

0.080.922

0.050.951

—0.35 0.65

(H2O)nCH3—NH3+n

NBO charges onCH3NH3

+•(H2O)n

B3LYP/6-311++G**

1 2 3 4 5

Experiment MM DFT

Exp Ele

n-decylamine

Electrostaticinteraction

∑∑=ij

jiel r

qi qjΣΣ=CH3NH3

(H2O)n–1

2 kcal/mol

1 2 3 4 5

Experiment MM DFT

Exp Ele

n-decylamine

Electrostaticinteraction

∑∑=ij

jiel r

qi qjΣΣ=CH3NH3

(H2O)n–1

vsExperimental

water binding energy(C10H21NH3

2 kcal/mol

1 2 3 4 56

18 Experiment MM DFT

ol) DFT

methylamine

Experimentn-decylamine

AMBERn-decylamine

NH CH C

CH C NH

Peptides

self-solvationH3C C NH2

δ–3.7 D

H3C C OH

O 1.7 D

lysine

Nα-acetyl-L-lysineAMBER

δ+⊕

Experimental binding energies(–∆H° in kcal/mol)

of nth water molecule

9.638.412.12

10.614.81

Nα-acetyl-L-lysine

n-decyl-amine

NH CH C

Ac-AAKAA

NH CH C

Ac-AAAAK

chargeremote

Ac-AAKAA vs Ac-AAAAK

8.5kcal/mol

experimentalwater binding

enthalpy6.9

kcal/mol

Ac-AxK

NH3+NH3+⊕δ–

α-helix

AMBER AMBERx = 8x = 20 Jarrold JACS (1998) 120, 12974

Experimental water binding energies (kcal/mol)

n/an/an/a

Ac-A20K

Ac-A8K

Ac-AAAAK

Ac-AAKAA

n-decylamine 101215

≤4n/an/an/a5n/an/an/a7n/an/an/a79n/an/a

First solvation shell Secondsolvation

shellChargeremote

10 8 8acetyllysine

a Estimated based on: Jarrold JACS (2002) 124, 11148

Ammonium Group

Entropy

(Arg–OMe + H)+ 9.2C10H21NH3+ 14.8

(Arg + H)+ 9.0(Ala-Ala + H)+ 14.8–∆H° (kcal/mol)–∆H° (kcal/mol)

GuanidineAmine

Experimental water binding energies

R = arginine

Ac-AAAAK vs Ac-AAAAR

ArgLys

⊕⊕

9.49.5

10.29.3

–∆H°kcal/mol

(Ac-AAAAK + H)+

(Ac-AAKAA + H)+

(AAAAA + H)+

C10H21NH3+

(AARAA-OMe + H)+

(Ac-AARAA + H)+6.9(AARAA + H)+8.5(RAAAA + H)+10.5

(Arg + H)+Exposed14.8

–∆H°kcal/mol

Self-solvated

Amines Guanidinespe

esExperimental water binding energies

Guanidines –∆H° kcal/mol

9.49.5

10.29.3

1st H2O

8.48.18.47.8

2nd H2O

3rd H2O

(AARAA-OMe + H)+

(Ac-AARAA + H)+

(AARAA + H)+

(RAAAA + H)+

Experimental water binding energies

Entropy

Carboxylate(Ala-Ala – H)–

Ammonium(Ala-Ala + H)+

H2N CH C

CH COO

H3N CH C

CH COOH

Ala-Ala

–∆H°kcal/mol

1st H2O 11.61st H2O

–∆H°kcal/mol

8.53rd H2O8.93rd H2O

9.42nd H2O10.52nd H2O

N CH C

+ 4 H2O

3AMBER

firstsolvationshell

(Ala-Ala – H)–

AMBER11.9

B3LYP/6-31G*

Calculated (B3LYP/6-31G*)water binding energy (kcal/mol)

(CH2)x

Peptide self-solvation

x=1 aspartic acidx=2 glutamic acid

(Ala-Ala) • (Ala-Ala – H)–

[(AA)2-H]-

0 2 4 6 8

(AA–H)–•(AA)•(H2O)m

(AA–H)–•(H2O)n

Monomer

160 180 200 220 240 260 280 300

320 340 360 380 400 420 440 460 480

1.3 Torr H2O, 260 K

⟨n⟩ – ⟨m⟩ ≅ 4

(AA–H)–•(H2O)5.2

Average: ⟨n⟩ = 5.2

(AA–H)–•(AA)•(H2O)1.3

Average: ⟨m⟩ = 1.3

(AA–H)–

(AA–H)–•(AA)

(AA–H)–•(H2O)4

Overlap of (AA–H)–

conformation in(AA–H)–

(AA–H)–•(H2O)4(AA–H)–•(AA)

Entropy

Experimental binding energiesof nth water molecule

13.4312.12

15.7114.81

–∆H°kcal/mol

n–∆H°kcal/mol

H3N H3N

CH3(CH2)9NH3+ H3N(CH2)12NH3

2+Blades, Klassen, KebarleJACS 118, 12437 (1996)

Na+ Ca2+n1 ~5524

(radius 0.97 Å) (radius 0.99 Å)

Na+ Ca2+n1 ~5524

(radius 0.97 Å) (radius 0.99 Å)

Hydration Mass SpectraNeurotensin

1.3 Torr H2O260 K

(ELYENKPRRPYIL)

820 840 860 880 900 920 940 960

560 580 600 620 640 660 680 700

1660 1700 1740 1780 1820

(M+2H)2+

(M+3H)3+

(M+H)+6

n −∆H°n (kcal/mol)

+1 +2 +3 1 9.2 10.3 (15) 2 9.8 8.9 (12) 3 (9) 9.6 9.5 4 (9) 9.4 9.3 5 8.5 9.4 6 (8) 9.8 7 (9) 8.8 8 (10) 9 (9) 10 (9)

Experimental ∆H°-values for binding nth water molecule to neurotensin (ELYENKPRRPYIL) in charge states +1, +2, and +3

± 0.3 kcal/mol± 1 kcal/mol for values in parenthesis

910 1210

+1 +2 +3 1 9.2 10.3 (15) 2 9.8 8.9 (12) 3 (9) 9.6 9.5 4 (9) 9.4 9.3 5 8.5 9.4 6 (8) 9.8 7 (9) 8.8 8 (10) 9 (9) 10 (9)

13.4312.12

15.7114.81

–∆H°kcal/mol

n–∆H°kcal/mol

13.4312.12

15.7114.81

–∆H°kcal/mol

n–∆H°kcal/mol

CH3(CH2)9NH3+ H3N(CH2)12NH3

2+Blades, Klassen, KebarleJACS 118, 12437 (1996)

NH3Degree of charge exposureNature of charged groups

+1 +2 +3 1 9.2 10.3 (15) 2 9.8 8.9 (12) 3 (9) 9.6 9.5 4 (9) 9.4 9.3 5 8.5 9.4 6 (8) 9.8 7 (9) 8.8 8 (10) 9 (9) 10 (9)

⊕⊕

Degree of charge exposureNature of charged groups

+1 +2 +3 1 9.2 10.3 (15) 2 9.8 8.9 (12) 3 (9) 9.6 9.5 4 (9) 9.4 9.3 5 8.5 9.4 6 (8) 9.8 7 (9) 8.8 8 (10) 9 (9) 10 (9)

Experimental ∆H°-values for binding nth water molecule to neurotensin (ELYENKPRRPYIL) in charge states +1, +2, and +3Experimental ∆H°-values for binding nth water molecule to neurotensin (ELYENKPRRPYIL) in charge states +1, +2, and +3

Experimental ∆H°-values for binding nth water molecule to neurotensin (ELYENK

Degree of charge exposureNature of charged groups

⊕⊕

Expect 15 kcal/mol for exposed ammonium

independent of the presence of other charges

(A) number of preferred hydration sites ∝ z(B) water binding energy ≠ f(z)

Multiply Charged Ions

(A) H3N

Entropy

Same sign vs opposite sign charges

Coulomb repulsion Coulomb attraction⊕

Salt Bridge

⊕δ+δ–

δ+δ–

Bradykinin

AMBER Barran, Liu, Wyttenbach, Bowers; unpublished

⊕δ+δ–

δ+δ–

⊕δ+δ–

δ+δ–

Experimental ∆H° and ∆S° values for bindingnth water molecule to bradykinin (M+H)+

2710.24

2610.13

2510.12

2610.71

–∆S°kcal/mol

–∆H°kcal/moln

±0.3 ±1

Bradykinin

Understand first steps of hydration:• Water binding sites• Energetics

for given peptide/protein structure.

However, peptide/protein structurechanges as hydration proceeds.

• Conformation• Zwitterion formation

Hydration Sites & Energies

Entropy

Change of Conformation

aqAlzheimer amyloid β-peptide

ESI IonSource

ESI IonSource MSMS Drift Cell

(helium)Drift Cell(helium) MSMS DetectorDetector

form M±z•(H2O)n in the source

Measure collision cross sections of hydrated ions in helium

Williams, J. Am. Soc. Mass Spectrom. 1997, 8, 565Beauchamp, J. Am. Chem. Soc. 1998, 120, 11758.

measure cross sections in heliumWyttenbach, Bowers, Top. Curr. Chem. 2003, 225, 207.

Entropy

H3N CH2 C

H2N CH2 C

Glycine

neutral

Gly zwitter-ion

TheoryJensen and Gordon JACS, 117, 8159 (1995)Gly•(H2O)2

12 kcal/mol

zwitter-ion

Photoelectron spectroscopyXu, Nilles, BowenJ.Chem.Phys., 119, 10696 (2003)

zwitter-ion

Gly•(H2O)5

Glycine

kcal/moldrop per H2O

NH NHO

D vs Lresidue

H2N NH2+

Peptides

H3N CH2 C

H2N NH2+

AARAAdifferent

RNHOR’

NH NHO

residue

H2N NH2+

500 502 504

458 460 462 464 466 468 4700

m/z72 474 476 4

AARAR = AcR’= H

gas-phaseH/D exchange

with D2O

R = HR’= H

R = H R’= CH3

zwitterion

+all1Hall1H

Wyttenbach, Paizs, Barran, Breci, Liu, Suhai, Wysocki, Bowers

JACS 125, 13768 (2003)

AARAAdifferent

+1.80.0

(AARAA)H+·H2O

+4.80.0

(AARAA)H+

Energy (kcal/mol)AMBER & B3LYP/6-31+G(d,p)

zwitterion

neutral termini

different

NH NHO

residue

H2N NH2+

JACS 125, 13768 (2003)kcal/mol

drop per H2OCAUTIONwith interpretation of

gas-phase H/D exchange

binding energy (kcal/mol)

10.2 ± 0.3Experiment

8.9Theory

B3LYP/6-31+G(d,p)BSSE & ZPE correction

(AARAA)H+···H2O

JACS 125, 13768 (2003)

C-terminus

N-terminus

JACS 125, 13768 (2003)

B3LYP/6-31+G(d,p)

set up forH/D exchange

relay mechanism

(AARAA)H+•H2ONeutral termini

(AARAA)H+•H2OZwitterion

C-terminus

N-terminus

JACS 125, 13768 (2003)

B3LYP/6-31+G(d,p)

(AARAA)H+•H2OTransition state

C-terminus

N-terminus

JACS 125, 13768 (2003)

B3LYP/6-31+G(d,p)

Entropy

–∆S°cal/mol/K

–∆H° kcal/mol

all other data:• all molecules• all charge states• all hydrates 1st–nth H2O

1st H2Oon small

molecules

2nd H2Oon small

molecules

1st H2Oon small

molecules

∆S° < 0loss of 3 translational

and 3 rotational degrees of freedom(gain of 6 vibrationaldegrees of freedom)

all datapositive andnegative ions

floppy

tightly bound H2O• large binding energy• large loss of entropy

strong entropy–enthalpy correlation (red data)

exceptions are:

• Addition of 1st H2O to small molecules (blue data) yields smaller than average loss of entropy→ floppy hydrates

• Addition of 2nd H2O to small molecules (yellow data) yields data between blue and red

Understand first steps of hydration:• Water binding sites• Water binding energies• Loss of entropy

Future challenges include:• Hydration beyond the first steps• Change of protein conformation• Zwitterion formationH

hydration of small peptides - uc santa barbara

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