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Centre for Extremophile Research

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Enzyme Thermostability and Thermoactivity

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CER Team






Staff - Prof. Michael Danson, Dr David Hough, Dr Susan Crennell, Prof. Robert Eisenthal.

We have determined the crystal structure of five citrate synthase molecules from different organisms that span the temperature range over which life exists (from psychrophile to hyperthermophile). Detailed structural analysis has revealed possible molecular mechanisms that determine the different stabilities of the five proteins. The key to these mechanisms is the precise structural location of the additional interactions. As one ascends the temperature ladder, the subunit interface of this dimeric enzyme and loop regions are reinforced by complex electrostatic interactions, and there is a reduced exposure of hydrophobic surface. These observations reveal a progressive pattern of stabilization through multiple additional interactions at solvent exposed, loop and interfacial regions.

(Taken from 'Bell GS, Russell RJ, Connaris H, Hough DW, Danson MJ, Taylor GL. Stepwise adaptations of citrate synthase to survival at life's extremes. From psychrophile to hyperthermophile. Eur J Biochem. 2002 Dec;269(24):6250-60.)

Temperature optima. Careful analysis of the dependence of enzyme activity on assay temperature has revealed that some enzymes might have real temperature optima in which the decrease in catalytic rate at temperatures above the optimum is not primarily a result of irreversible thermal inactivation. The 'equilibrium model' has been formulated to describe genuine temperature optima, and to suggest a simple experimental method by which to distinguish these cases from those in which enzyme instability is the major determinant of temperature optima.

(Taken from 'Daniel RM, Danson MJ, Eisenthal R. The temperature optima of enzymes: a new perspective on an old phenomenon. Trends Biochem Sci. 2001 Apr;26(4):223-5.')

Cellulases. We have determined the X-ray crystal structure of Rhodothermus marinus cellulase Cel12A which has a half-life of more than two hours at 90oC and a temperature optimum exceeding 90oC. Comparison to mesophilic homologues revealed a large increase in surface ion pairs, which may be the main determinant of the hyperthermostability. Structures of the enzyme in complex with substrate show an increase in aromatic interactions in the active site cleft, contributing to its ability to bind cellulose at high temperature.

Structure of Cel12A with substrate (cellotetraose, drawn with yellow bonds) bound in the active site. Cellulase Cel12A










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