title: Thermodynamic molecular switch in macromolecular interactions.
abstract: It is known that most living systems can live and operate optimally only at a sharply defined temperature, or over a limited temperature range, at best, which implies that many basic biochemical interactions exhibit a well-defined Gibbs free energy minimum as a function of temperature. The Gibbs free energy change, deltaG(o) (T), for biological systems shows a complicated behavior, in which deltaG(o)(T) changes from positive to negative, then reaches a negative value of maximum magnitude (favorable), and finally becomes positive as temperature increases. The critical factor in this complicated thermodynamic behavior is a temperature-dependent heat capacity change (deltaCp(o)(T) of reaction, which is positive at low temperature, but switches to a negative value at a temperature well below the ambient range. Thus, the thermodynamic molecular switch determines the behavior patterns of the Gibbs free energy change, and hence a change in the equilibrium constant, Keq, and/or spontaneity. The subsequent, mathematically predictable changes in deltaH(o)(T), deltaS(o)(T), deltaW(o)(T), and deltaG(o)(T) give rise to the classically observed behavior patterns in biological reactivity, as demonstrated in three interacting protein systems: the acid dimerization reaction of alpha-chymotrypsin at low pH, interaction of chromogranin A with the intraluminal loop peptide of the inositol 1,4,5-triphosphate receptor at pH 5.5, and the binding of L-arabinose and D-galactose to the L-arabinose binding protein of Escherichia coli. In cases of protein unfolding of four mutants of phage T4 lysozyme, no thermodynamic molecular switch is observed.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine, Gainesville 32610-0245, USA. pwchun@biochem.med.ufl.edu
authors.forename: P W
authors.initials: PW
authors.lastname: Chun
mesh_terms: D001089:Arabinose / Q000378:metabolism; D015220:Calcium Channels / Q000737:chemistry; D002151:Calorimetry; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism; D053379:Chromogranin A; D002864:Chromogranins / Q000737:chemistry; D002918:Chymotrypsin / Q000737:chemistry; D019281:Dimerization; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins; D005690:Galactose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D053496:Inositol 1,4,5-Trisphosphate Receptors; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics
chemical_list: C016242:AraF protein, E coli; D015220:Calcium Channels; D002352:Carrier Proteins; D053379:Chromogranin A; D002864:Chromogranins; D029968:Escherichia coli Proteins; D053496:Inositol 1,4,5-Trisphosphate Receptors; D011506:Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D001089:Arabinose; D002918:Chymotrypsin; D005690:Galactose