Biophys J, September 2000, p. 1180-1187, Vol. 79, No. 3

Association Entropy in Adsorption Processes

Nir Ben-Tal,^* Barry Honig, Carey K. Bagdassarian, and Avinoam Ben-Shaul^§

 ^*Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel;  Department of Biochemistry and Molecular Biophysics, and Center for Biomolecular Simulations, Columbia University, New York, New York 10032 USA;  Department of Chemistry, The College of William and Mary, Williamsburg, Virginia 23187-8795 USA; and  ^§Department of Physical Chemistry and The Fritz Haber Research Center, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

The association of two species to form a bound complex, e.g., the binding of a ligand to a protein or the adsorption of a peptide on a lipid membrane, involves an entropy loss, reflecting the conversion of free translational and rotational degrees of freedom into bound motions. Previous theoretical estimates of the standard entropy change in bimolecular binding processes, S^o, have been derived from the root-mean-square fluctuations in protein crystals, suggesting S^o  50 e.u., i.e., TS°  25 kT = 15 kcal/mol. In this work we focus on adsorption, rather than binding processes. We first present a simple statistical-thermodynamic scheme for calculating the adsorption entropy, including its resolution into translational and rotational contributions, using the known distance-orientation dependent binding (adsorption) potential. We then utilize this scheme to calculate the free energy of interaction and entropy of pentalysine adsorption onto a lipid membrane, obtaining TS^o  1.7 kT  1.3 kcal/mol. Most of this entropy change is due to the conversion of one free translation into a bound motion, the rest arising from the confinement of two rotational degrees of freedom. The smaller entropy loss in adsorption compared to binding processes arises partly because a smaller number of degrees of freedom become restricted, but mainly due to the fact that the binding potential is much "softer."

Biophys J, September 2000, p. 1180-1187, Vol. 79, No. 3
© 2000 by the Biophysical Society   0006-3495/00/09/1180/08  $2.00

This article has been cited by other articles:

				M. B. Ulmschneider, J. P. Ulmschneider, M. S. P. Sansom, and A. Di Nola A Generalized Born Implicit-Membrane Representation Compared to Experimental Insertion Free Energies Biophys. J., April 1, 2007; 92(7): 2338 - 2349. [Abstract] [Full Text] [PDF]

				R. Alsallaq and H.-X. Zhou Energy Landscape and Transition State of Protein-Protein Association Biophys. J., March 1, 2007; 92(5): 1486 - 1502. [Abstract] [Full Text] [PDF]

				M. F. Hagan and D. Chandler Dynamic Pathways for Viral Capsid Assembly Biophys. J., July 1, 2006; 91(1): 42 - 54. [Abstract] [Full Text] [PDF]

				I. Oren, S. J. Fleishman, A. Kessel, and N. Ben-Tal Free Diffusion of Steroid Hormones Across Biomembranes: A Simplex Search with Implicit Solvent Model Calculations Biophys. J., August 1, 2004; 87(2): 768 - 779. [Abstract] [Full Text] [PDF]

				H. Luo and K. Sharp On the calculation of absolute macromolecular binding free energies PNAS, August 6, 2002; 99(16): 10399 - 10404. [Abstract] [Full Text] [PDF]