Protein elastic forces

Zentz et al (2003) applied equation 5.29 to investigate the protein elastic forces responsible for the Trp angular displacement inside the apoHb molecule. In fact, at each temperature (T), a certain amount of the energy (W) from the thermal bath is converted into mechanical energy... 

Another AFM-based technique is chemical force microscopy (CFM) (Friedsam et al. 2004 Noy et al. 2003 Ortiz and Hadziioaimou 1999), where the AFM tip is functionalized with specific chemicals of interest, such as proteins or other food biopolymers, and can be used to probe the intermolecular interactions between food components. CFM combines chemical discrimination with the high spatial resolution of AFM by exploiting the forces between chemically derivatized AFM tips and the surface. The key interactions involved in food components include fundamental interactions such as van der Waals force, hydrogen bonding, electrostatic force, and elastic force arising from conformation entropy, and so on. (Dther interactions such as chemical bonding, depletion potential, capillary force, hydration force, hydrophobic/ hydrophobic force and osmotic pressure will also participate to affect the physical properties and phase behaviors of multicomponent food systems. Direct measurements of these inter- and intramolecular forces are of great interest because such forces dominate the behavior of different food systems. 

EUehauge, E., Norregaard-Madsen, M. and Sogaard-Andersen, L. (1998). The FruA signal transduction protein provides a checkpoint for the temporal coordination of intercellular signals in M. xanthus development. Md. Microbiol. 30, 807-817. Fontes, M. and Kaiser, D. (1999). Myxococcus cells respond to elastic forces in their substrate. Proc. Natl. Acad. Sci. U.S.A. 96, 8052-8057. 

Figure 5.8. Hydrophobic association to produce increased elastic force at fixed length, as experimentally shown in Figure 5.7. (Top) A series of clamshaped globular proteins, strung together by an elastic band attached near the mouth, are at equilibrium between open and closed states due to hydrophobic association. As the distribution shifts toward more closed states, the elastic force increases. (Bottom) A P-spiral with an equilibrium between...

D.W. Urry, Entropic Elastic Processes in Protein Mechanism. II. Simple (Passive) and Coupled (Active) Development of Elastic Forces. J. Protein Chem., 1,81-114,1988, especially Figure 12. 

Complex III is an example of the consilient mechanism for elasticity that includes the coupling of hydrophobic association with development of an elastic force. In particular, the Rieske iron protein (RIP) of Complex III resides on the cytoplasmic side and contains a long hydrophobic a-helix that passes through the lipid bilayer from the cytoplasmic side to emerge on the matrix side with charged residues that combine to anchor the iron protein to the membrane. On the cytoplasmic side, a sequence of about 15 residues that is continuous with the transmembrane anchor... 

The second point addresses the nature of elastic force development in relation to imder-standing efficient energy conversion. If the energy required for chain deformation during elastic force development becomes lost to other parts of the protein and to the surrounding water, then so too is efficient energy conversion lost. In other words, elastomeric force development on deformation in a protein-based machine followed by marked hysteresis on relaxation necessarily denotes an inefficient protein-based machine. 

Similarly, apolar-polar repulsion between a highly charged group and very hydrophobic side chains of a chain or loop of protein would be expected to limit the freedom of rotation about backbone bonds of sufficiently kineti-cally free chain segment or loop. This increase in AG,p would decrease the number of states accessible to the polymer and decrease the entropy of the chain. The resulting development of an elastic force in the chain segment or loop of protein could be used to perform... 

The operative component of the comprehensive hydrophobic effect arises from the competition between charged and oil-like groups. This was shown to result in a previously unknown repulsive force embodied within an interaction energy called an apolar-polar repulsive free energy of hydration, AG,p. During function, AG,p works in conjunction with elastic force development by the restriction of internal chain dynamics. These have been called the hydrophobic and elastic consilient mechanisms. In Chapters 6,7, and 8, these consilient mechanisms were demonstrated to be fundamental to understanding the functions of biology s proteins. 

Elastic forces come into play as hydrophobic associations stretch interconnecting chain segments. Only if the elastic deformation is ideal does all of the energy of deformation become recovered on relaxation. To the extent that hysteresis occurs in the elastic deformation/ relaxation, energy is lost and the protein-based machine loses efficiency. Thus, the elastic consilient mechanism, whereby the force-extension curve can be found to overlay the force-relaxation curve becomes the efficient mechanical coupler within the vital force. The objective now becomes one of understanding the age-old problem of a reluctance to discard past idols. 

Figure 10. Cartoon of the relationship between hydrophobic association and entropic elastic force development. Above A series of clam-shaped globular protein strung together by elastic bands with an equilibrium between open and hydrophobically associated closed states. Clearly, as the equilibrium shifts toward more closed states, the force, sustained by the interconnecting elastic segments, increases. Below Representation of the p-spiral structure of...

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