Specific Recognition Force, Dissociation and Thermodynamics of Single-pair Antibody-Antigen Interaction Using Atomic Force Microscopy
Date Issued
2006
Date
2006
Author(s)
Wang, Yu-Ming
DOI
en-US
Abstract
Molecular recognition and intermolecular binding are essential for implementing many biochemical and biological processes in living organisms. To further understand the molecular binding mechanisms, this study used atomic force microscopy as a force-based senor for investigation of the force strength between antibody and antigen complex in a single pair level with varied physiological (pH and temperature) and physical (loading rate) conditions. The results provided direct evidence of unbinding force, dissociation rate and thermodynamic parameters that explained intermolecular behavior of human IgG1/anti-human IgG1 complex and glucagon/anti-glucagon IgG complexes, respectively.
Mean measured forces of human IgG1 and its specific antibody system with pH-varied liquid environments showed a sharp decrease with a decrease of pH value (acidic environment), and a gradual decrease with an increase of pH value (alkaline environment) from a reference level at neutrality. This could have corresponded to the pH-induced change in conformational change and outer functional groups of amino acids which are protonated. As a result of change in pH environment of human IgG1/anti-human IgG1 complex, surface protonated properties and conformation weakened intermolecular force. Molecular dynamic behavior and free energy change were also contributed to a high probability of bonds breaking and a low magnitude of energy barrier when molecules were immersed in acidic or alkaline solution. Temperature-dependent unbinding force experiments were also carried out. The results showed that the unbinding forces decreased with an increase of environmental temperatures. This could be largely due to temperature-induced conformational change in volume expansion and strong Brownian motion. As a result, interaction forces decreased. Estimated dynamic behavior and thermodynamic parameters also showed weak interactions under high temperatures. This could have corresponded to looser molecular structure and weaker intermolecular interaction in high temperature, thereby increasing entropy and enthalpy.
The interaction between glucagon and anti-glucagon IgG with pH- varied liquid environment exhibited weak interaction force, low energy barriers and high dissociation rates under acidic and alkaline solutions. This indicated that molecular interactions turned out weak forces when pH values increased or decreased away from neutrality. Force measurement as a function of temperature exhibited a nearly linear decrease of force strength with an increase of temperature. This could have been attributed to molecular charge-free conformational changes, resulting in incomplete binding. The thermodynamic enthalpy and entropy for interaction showed an increase with increasing temperature.
Specific interactions of human IgG1/anti-human IgG1 pairs and glucagon/anti-glucagon IgG pairs have been successfully investigated by the atomic force microscope. With the use of an extended Bell and Evans model, the molecular dynamic behavior, free energy change and thermodynamic parameters can be obtained by varying physiological (pH and temperature) and physical (loading rate) conditions. The results provided directly evidence to explain the biological interactions.
Subjects
原子力顯微鏡
單一生物分子間交互作用力
自由能
解離熵
解離焓
atomic force microscopy
dissociation rate
enthalpy
entropy
Type
thesis
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