title: The effect of calcium binding on the unfolding barrier: A kinetic study on homologous alpha-amylases.
abstract: Extreme thermostabilities of proteins can be achieved by binding co-factors to the protein structures. For various alpha-amylases protein stabilization upon calcium binding is a well-known phenomenon. In the present study the mechanism of stabilization of three homologous alpha-amylases was investigated by measuring the unfolding kinetics with CD spectroscopy. For this purpose thermal unfolding kinetics of calcium saturated and calcium depleted enzymes were analyzed by means of Eyring-plots. The free energy change between the native and the transition state which characterized the unfolding barrier height was found to be proportional to the number of calcium ions bound to the protein structures. For the most thermostable alpha-amylases calcium binding caused a significant increase in the enthalpy change, which was partly compensated by increased entropy changes.
authors.affiliation: Research Centre Jülich, Germany.
authors.forename: Arpana
authors.initials: A
authors.lastname: Kumari
authors.forename: Tobias
authors.initials: T
authors.lastname: Rosenkranz
authors.forename: Arvind M
authors.initials: AM
authors.lastname: Kayastha
authors.forename: Jörg
authors.initials: J
authors.lastname: Fitter
mesh_terms: D002118:Calcium / Q000737:chemistry*; D002942:Circular Dichroism; D019791:Guanidine / Q000737:chemistry; D007700:Kinetics; D011485:Protein Binding; D011489:Protein Denaturation; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D013696:Temperature; D013816:Thermodynamics; D000516:alpha-Amylases / Q000737:chemistry*
chemical_list: D000516:alpha-Amylases; D019791:Guanidine; D002118:Calcium