A chemically modified α-amylase with a molten-globule state has entropically driven enhanced thermal stability

• The thermostability properties of TAA were investigated by chemically modifying carboxyl groups on the surface of the enzyme with AMEs. The TAAMOD exhibited a 200 improvement in starch-hydrolyzing productivity at 60°C. By studying the kinetic, thermodynamic and biophysical properties, we found that TAAMOD had formed a thermostable, MG state, in which the unfolding of the tertiary structure preceded that of the secondary structure by at least 20°C. The X-ray crystal structure of TAAMOD revealed no new permanent interactions (electrostatic or other) resulting from the modification. By deriving thermodynamic activation parameters of TAAMOD, we rationalised that thermostabilisation have been caused by a decrease in the entropy of the transition state, rather than being enthalpically driven. Far-UV CD shows that the origin of decreased entropy may have arisen from a higher helical content of TAAMOD. This study provides new insight into the intriguing properties of an MG state resulting from the chemical modification of TAA.

Ämnesord

NATURVETENSKAP  -- Biologi -- Biokemi och molekylärbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Biochemistry and Molecular Biology (hsv//eng)

Nyckelord

activation thermodynamics

calorimetry

entropy

enzyme kinetics

protein X-ray crystallographic structure

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