Hydration of Small Peptides Thomas Wyttenbach, Dengfeng Liu, and - PowerPoint PPT Presentation

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?

Alzheimer amyloid β -peptide apolar solvent (NMR) 1 water (theory) 3 gas phase water: 2 (theory) 3 1 Crescenzi et al • no NMR structure Eur J Biochem 269, 5642 (2002) • no α -helix 2 Zhang et al J Struct Biology 130, • no β -sheet 130 (2000) 3 Baumketner, Shea • hydrophobic core UCSB, unpublished

Why study hydration? Bridge gas phase and solution phase Study effect of individual water molecules on solute molecules • energetics (water binding energy) • structure � conformations, folding � zwitterion formation � hydration sites

Myoglobin NMR structure

Mass Spectra Neurotensin 1 H 2 O (ELYENKPRRPYIL) (M+H) + 2 torr H 2 O 286 K 1 3 (M+2H) 2+ 6 2 0 9 (M+3H) 3+ m/z

Instrumentation ESI Ion Ion Drift ESI Ion Ion Drift MS Detector MS Detector Source Funnel Cell Source Funnel Cell Liquid N 2 cooling H 2 O M + •(H 2 O) n M + ~1 torr H 2 O Electrical heaters

drift time Mass Spectra Neurotensin 1 H 2 O 900 µ s (ELYENKPRRPYIL) (M+H) + 2 torr H 2 O Equilibrium? 286 K 1 YES 3 � (M+2H) 2+ 1800 µ s 6 2 H 2 O 0 9 (M+3H) 3+ m/z 2700 µ s M + •(H 2 O) n M + ~1 torr H 2 O m/z Neurotensin (M+2H) 2+ 290 K, 1.8 torr H 2 O

Data Analysis Data Analysis ratio of Mass Spectra Neurotensin 1 H 2 O peak intensities (ELYENKPRRPYIL) (M+H) + 2 torr H 2 O Equilibrium? 286 K 1 equilibrium YES 3 � constant (M+2H) 2+ 6 2 H 2 O van’t Hoff 0 9 (M+3H) 3+ m/z ∆ H ° and ∆ S ° M + •(H 2 O) n M + ∆ H ° ∆ S ° ~1 torr H 2 O + ⊕ ⊕

Charged groups are important. In peptides and • Amine proteins they are: � lys � N-terminus • Guanidine � arg • Imidazole � his • Carboxylate � asp � glu � C-terminus

HYDRATION OF PEPTIDES HYDRATION OF PEPTIDES HYDRATION OF PEPTIDES Ionic Groups � � � The Ammonium Group � The Guanidinium Group � The Carboxylate Group Several Ionic Groups � Multiply Charged Ions � Salt Bridges Challenges Ahead � Change of Conformation � Zwitterion Formation � Entropy

+ CH 3 NH 3 2 second solvation shell 3 4 1 B3LYP/6-311++G**

n -decylamine 18 Experiment Water binding energy (kcal/mol) MM 16 DFT 14 first solvation shell Molecular 12 Mechanics AMBER, TIP3P 10 second solvation shell 8 Experiment 6 1 2 3 4 5 Number of water molecules

δ + δ – ⊕ Ionic hydrogen bond: electrostatic interaction important

17 kcal/mol 15 kcal/mol experiment 1 experiment 2 & DFT 2 ⊕ ⊕ δ + 1 Meot-Ner JACS 1984 , 106 , 1265 2 Liu, Wyttenbach, δ + Barran, Bowers, JACS 2003 , 125 , 8458

δ + ⊕ δ +

M + •(H 2 O) n ∆ H ° n kcal/mol 1 15 2 12 3 10

NBO charges on CH 3 NH 3+• (H 2 O) n n CH 3 —NH 3+ (H 2 O) n 0.35 0.65 0 — 1.00 1 0.95 0.05 2 0.92 0.08 3 0.90 0.10 B3LYP/6-311++G**

q i q j q j q j q q Σ Σ ∑ ∑ i j = E = Experiment el etc. etc. r q i q i n-decylamine n th + CH 3 NH 3 ij MM H 2 O (H 2 O) n –1 Electrostatic energy E el DFT etc. etc. Exp n–1 n–1 Electrostatic Ele interaction 2 kcal/mol 1 2 3 4 5 Number of water molecules

q i q j q q Σ Σ Experimental ∑ ∑ i j = E vs = water binding energy Experiment el r + ) n-decylamine (C 10 H 21 NH 3 n th + CH 3 NH 3 ij MM H 2 O (H 2 O) n –1 DFT Exp Electrostatic Ele interaction 2 kcal/mol 1 2 3 4 5 Number of water molecules

18 DFT Experiment Water binding energy (kcal/mol) methylamine MM 16 DFT 14 12 10 AMBER Experiment n -decylamine 8 n -decylamine 6 1 2 3 4 5 Number of water molecules

Peptides lysine δ – NH 3 O 3.7 D self-solvation CH 2 H 3 C C NH 2 δ + CH 2 CH 2 O O O CH 2 δ – O 1.7 D C NH C NH CH C NH CH R C OH H 3 C δ +

N α -acetyl- L -lysine AMBER

δ + ⊕ Experimental binding energies (– ∆ H° in kcal/mol) of n th water molecule N α -acetyl- n -decyl- n amine L -lysine OH 1 14.8 10.6 2 12.1 8.4 3 9.6 AMBER

Ac-AAKAA O O O O O O H 3 C C NH CH C NH CH C NH CH C NH CH C NH CH C OH CH 3 CH 3 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 NH 2 AMBER

Ac-AAAAK O O O O O O H 3 C C NH CH C NH CH C NH CH C NH CH C NH CH C OH CH 3 CH 3 CH 3 CH 3 CH 2 CH 2 CH 2 CH 2 charge NH 2 remote AMBER

Ac-AAKAA vs Ac-AAAAK experimental 8.5 6.9 water binding kcal/mol kcal/mol enthalpy AMBER

Ac-A x K AMBER AMBER x = 8 x = 4 x = 20 Jarrold JACS (1998) 120, 1297 4 ⊕ δ – + + NH 3 NH 3 α -helix (c) δ +

Ammonium Group Experimental water binding energies (kcal/mol) First solvation shell Second Charge solvation remote 1 2 3 shell n -decylamine 15 12 10 8 10 8 8 n/a acetyllysine n/a n/a 9 7 7 Ac-AAKAA n/a n/a n/a n/a 7 Ac-AAAAK n/a n/a n/a n/a 5 Ac-A 8 K a ≤ 4 n/a n/a n/a n/a Ac-A 20 K a Estimated based on: Jarrold JACS (2002) 124, 11148

HYDRATION OF PEPTIDES HYDRATION OF PEPTIDES HYDRATION OF PEPTIDES Ionic Groups � � The Ammonium Group � � The Guanidinium Group � The Carboxylate Group Several Ionic Groups � Multiply Charged Ions � Salt Bridges Challenges Ahead � Change of Conformation � Zwitterion Formation � Entropy

Experimental water binding energies Amine Guanidine O CH 3 NH 2 O H N NH NH 3 NH 2 HO HO O CH 3 NH 2 – ∆ H ° (kcal/mol) – ∆ H ° (kcal/mol) 14.8 9.0 (Ala-Ala + H) + (Arg + H) + 14.8 9.2 C 10 H 21 NH 3 + (Arg–OMe + H) +

H H N N H C H N H R = arginine

Ac-AAAAK vs Ac-AAAAR Arg Lys ⊕ ⊕ AMBER

Experimental water binding energies Amines Guanidines – ∆ H ° – ∆ H ° kcal/mol kcal/mol C 10 H 21 NH 3 Exposed (Arg + H) + + 14.8 9.0 (AAAAA + H) + 10.5 (RAAAA + H) + 9.3 pentapeptides (Ac-AAKAA + H) + 8.5 (AARAA + H) + 10.2 Self- (Ac-AAAAK + H) + (Ac-AARAA + H) + 6.9 9.5 solvated (AARAA-OMe + H) + 9.4

Experimental water binding energies – ∆ H ° Guanidines kcal/mol 1 st H 2 O 2 nd H 2 O 3 rd H 2 O (RAAAA + H) + 9.3 7.8 7.1 (AARAA + H) + 10.2 8.4 (Ac-AARAA + H) + 9.5 8.1 (AARAA-OMe + H) + 9.4 8.4 7.6

HYDRATION OF PEPTIDES HYDRATION OF PEPTIDES HYDRATION OF PEPTIDES Ionic Groups � � The Ammonium Group � � The Guanidinium Group � � The Carboxylate Group Several Ionic Groups � Multiply Charged Ions � Salt Bridges Challenges Ahead � Change of Conformation � Zwitterion Formation � Entropy

Ala-Ala Ammonium Carboxylate (Ala-Ala – H) – (Ala-Ala + H) + O O H 3 N CH C N CH COOH H 2 N CH C N CH COO H H CH 3 CH 3 CH 3 CH 3 – ∆ H ° – ∆ H ° kcal/mol kcal/mol 1 st H 2 O 14.8 1 st H 2 O 11.6 2 nd H 2 O 10.5 2 nd H 2 O 9.4 3 rd H 2 O 8.9 3 rd H 2 O 8.5

CH 3 O N CH C + 4 H 2 O O H 1 first solvation 2 4 shell 3 AMBER

(Ala-Ala – H) – Calculated (B3LYP/6-31G*) water binding energy ( kcal/mol ) 15.6 13.1 11.9 AMBER B3LYP/6-31G*

Peptide self-solvation O O O CH C N CH C N CH C CH 3 H (CH 2 ) x H CH 3 C O O x=1 aspartic acid x=2 glutamic acid

(Ala-Ala) • (Ala-Ala – H) – AMBER

0 2 4 6 8 n 1.3 Torr H 2 O, 260 K (AA–H) – •(H 2 O) 5.2 (AA–H) – •(H 2 O) n 319 Monomer 3 Average: 〈 n 〉 = 5.2 8 160 180 200 220 240 260 280 300 - [(AA) 2 -H] (AA–H) – •(AA)•(H 2 O) 1.3 (AA–H) – •(AA)•(H 2 O) m Dimer 3 Average: 〈 m 〉 = 1.3 4 〈 n 〉 – 〈 m 〉 ≅ 4 320 340 360 380 400 420 440 460 480 m/z

(AA–H) – AMBER

(AA–H) – •(AA) AMBER

(AA–H) – •(H 2 O) 4 AMBER

Overlap of (AA–H) – conformation in � (AA–H) – � (AA–H) – •(H 2 O) 4 � (AA–H) – •(AA) AMBER

HYDRATION OF PEPTIDES HYDRATION OF PEPTIDES HYDRATION OF PEPTIDES Ionic Groups � � The Ammonium Group � � The Guanidinium Group � � The Carboxylate Group Several Ionic Groups � � Multiply Charged Ions � Salt Bridges Challenges Ahead � Change of Conformation � Zwitterion Formation � Entropy

Experimental binding energies of n th water molecule CH 3 (CH 2 ) 9 NH 3+ H 3 N(CH 2 ) 12 NH 32+ H 3 N H 3 N Blades, Klassen, Kebarle JACS 118 , 12437 (1996) – ∆ H ° – ∆ H ° n n kcal/mol kcal/mol 1 1 14.8 15.7 2 15.7 2 3 12.1 13.4 NH 3 4 13.6 n n Na + Na + Ca 2+ Ca 2+ 1 1 24 24 ~55 ~55 ( radius 0.97 Å) ( radius 0.97 Å) ( radius 0.99 Å) ( radius 0.99 Å)

3 Hydration Mass Spectra Neurotensin 0 6 (ELYENKPRRPYIL) (M+H) + 1660 1700 1740 1780 1820 1.3 Torr H 2 O 6 260 K 9 3 12 0 (M+2H) 2+ 820 840 860 880 900 920 940 960 12 15 9 18 H 2 O 0 (M+3H) 3+ 560 580 600 620 640 660 680 700 m/z