Thermodynamic Study of Interactions Between ZnO and ZnO Binding Peptides Using Isothermal Titration Calorimetry

Abstract

Whilst material specific peptide binding sequences have been identified using a combination of combinatorial methods and computational modelling tools, a deep molecular level understanding of the fundamental principles through which these interactions occur and in some instances modify the morphology of inorganic materials is far from being fully realized. Understanding the thermodynamic changes that occur during peptide-inorganic interactions and correlating these to structural modifications of the inorganic materials could be the key to achieving and mastering control over material formation processes. This study is a detailed investigation applying isothermal titration calorimetry (ITC) to directly probe thermodynamic changes that occur during interaction of ZnO binding peptides (ZnO-BPs) and ZnO. The ZnO-BPs used are reported sequences G-12 (GLHVMHKVAPPR), GT-16 (GLHVMHKVAPPR-GGGC) and alanine mutants of G-12 (G-12A6, G-12A11 and G-12A12) whose interaction with ZnO during solution synthesis studies have been extensively investigated. The interactions of the ZnO-BPs with ZnO yielded biphasic isotherms comprising both an endothermic and an exothermic event. Qualitative differences were observed in the isothermal profiles of the different peptides and ZnO particles studied. Measured ∆G values were between -6 and -8.5 kcal/mol and high adsorption affinity values indicated the occurrence of favourable ZnO-BP-ZnO interactions. ITC has great potential in its use to understand peptide-inorganic interactions and with continued development, the knowledge gained may be instrumental for simplification of selection processes of organic molecules for the advancement of material synthesis and design.

Polariton condensation and surface enhanced Raman in spherical ZnO microcrystals

“…In contrast to the surface plasmon of collective oscillations of conduction electrons in metals 42 , the considered mechanism would borrow from the leaky field part of the interacting polaritons. To test this, we explored the interaction of the zinc oxide specific G12 polypeptide 25 . In Fig.…”

“…Zinc oxide microcrystals (average size of 100 μm) are the analytical standard from Sigma-Aldrich, CAS Number 1314-13-2. We synthesize ZnO microspheres and G12 polypeptide as reported previously 20,25 : for details see Supplementary Note 1. Using PANalytical X'Pert PRO X-ray diffractometer (Malvern Panalytical, Malvern, UK) with Cu Kα radiation at 1.54056 Å we extract the crystallite domain sizes of 52 ± 9 and 18 ± 5 nm for microcrystals and microspheres, respectively 44 .…”

“…At the high-power limit, the leaky field component of the polaritons provides the opportunity for surface field enhancement behaviour. Indeed, using the discovered regime, we observed surface enhanced Raman for GLHVMHKVAPPR (G12) polypeptide that we have previously used to investigate the thermodynamics of interaction with zinc oxide 25 , and for Si–O − stretching vibrations in Q 3 -structural elements 26 , 27 of a borosilicate glass in contact with ZnO microspheres. The surface polariton field enhancement (SPFE) mechanism reported here opens up opportunities for research and engineering of bio-inorganic and inorganic composites using zinc oxide as both a structural and sensing element.…”

Experimental characterization and simulation of amino acid and peptide interactions with inorganic materials

“…Hence, changes in enthalpy due to dissolution, aggregation and peptide folding interfere with adsorption effects revealing a problem in the evaluation of experiments . Limo and Perry verified the high affinity (0.7–22 μM) of zinc oxide binding peptides (GLHVMHKVAPPR‐X; single letter amino acid code) to zinc oxide rods and platelets by ITC .…”

Caracterización Biofisicoquímica de la interacción superficie proteínica del Fago M13 con cristales inorgánicos

“…Por ejemplo, con la técnica de calorimetría de titulación isotérmica (ITC) se puede medir de forma muy precisa el calor de interacción entre dos moléculas y con la medición de este calor se pueden calcular las constantes de unión, la estequiometría de la reacción y los parámetros termodinámicos como el cambio en la entalpía ∆ , la energía libre de Gibbs ∆ y la entropía ∆ 12,13 . De este modo, Limo et al 14 reportaron un estudio de interacción entre partículas de ZnO y péptidos con afinidad a este material usando la técnica de ITC. Si bien es una técnica muy poderosa y, determinaron que una interacción favorable de interacción tiene un valor de ∆ entre -6.0 y -8.5 kcal/mol, hacen notar que es un proceso complejo que involucra interacciones simultáneas como son: péptido-solvente, sustratosolvente, péptido-sustrato, y donde posiblemente la conformación del péptido es muy diferente en cada tipo de interacción.…”