Thermal Destabilization of Stem Bromelain by Trehalose
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Trehalose, a naturally occurring osmolyte, is considered as a universal protein stabilizer. We investigated the effect of the disaccharides, trehalose and sucrose, on the thermal stability and conformation of bromelain. To our surprise, bromelain in the presence of 1 M trehalose/sucrose was destabilized under thermal stress. The average Tm values as determined by UV spectroscopy and CD spectropolarimetry decreased by 5° and 7°C for bromelain in 1 M sucrose or trehalose solutions, respectively. The enzyme was also found to inactivate faster at 60°C in the presence of these osmolytes. The tertiary and secondary structure of bromelain undergoes small changes in the presence of sucrose/trehalose. Studies on the binding of these osmolytes with the native and the heat denatured enzyme revealed that sucrose/trehalose lead to preferential hydration of the denatured bromelain as compared to the native one, hence stabilizing more the denatured conformation. This is perhaps the first report on the destabilization of a protein by trehalose.
KeywordsDestabilization stem bromelain temperature trehalose
pineapple stem bromelain
mid-point of thermal transition
sodium dodecyl sulphate-polyacylamide gel electrophoresis.
Facilities provided by Aligarh Muslim University are gratefully acknowledged. The work was also supported by the department of Science and Technology, Government of India, under its FIST programme, and the University Grants Commission, India under its special assistance programme.
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