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Glycoconjugate Journal

, 26:1075 | Cite as

Spectroscopic and differential scanning calorimetric studies on the unfolding of Trichosanthes dioica seed lectin. Similar modes of thermal and chemical denaturation

  • M. Kavitha
  • Musti J. Swamy
Article

Abstract

Physico-chemical and unfolding studies have been carried out on Trichosanthes dioica seed lectin (TDSL). The lectin exhibited maximum activity between pH 7.0 and 10.0, which decreased steeply at lower pH. The hemagglutination activity of TDSL was unaffected in the temperature range 4–50°C, but decreased rapidly at higher temperatures. Differential scanning calorimetric studies indicate that thermal unfolding of TDSL is an irreversible process, which could be described by a three-state model. The calorimetric scan recorded at pH 7.0 consists of two transitions, occurring at around 338.6 K, and 342.8 K. In the presence of carbohydrate ligands both these transitions shifted to higher temperatures, suggesting that ligand binding stabilizes the native conformation of the protein. The unfolding temperature was highest at pH 5.0 indicating that TDSL is more stable at acidic pH. Gdn.HCl induced unfolding, monitored by following changes in the intrinsic fluorescence properties of the protein, was also observed to be a three-state process involving an intermediate. CD spectroscopy indicates that the secondary and tertiary structures of TDSL are rather similar at different pH values, indicating that the lectin structure remains essentially unchanged over a wide range of pH.

Keywords

Agglutinin Carbohydrate binding protein Thermal unfolding Van’t Hoff enthalpy Calorimetric enthalpy Chemical denaturation 

Abbreviations

TDSL

Trichosanthes dioica seed lectin

CD

Circular dichroism

ΔCp

Change in excess heat capacity

DSC

Differential scanning calorimetry

GalNAc

N-acetyl-D-galactosamine

Gdn.HCl

Guanidine hydrochloride

ΔHc

Change in calorimetric enthalpy

ΔHv

Change in van’t Hoff enthalpy

MeαGal

Methyl-α-D-galactopyranoside

MeβGal

Methyl-β-D-galactopyranoside

Tm

Transition temperature

Notes

Acknowledgements

This work was supported by a research grant from the Department of Biotechnology (India) to MJS. MK is supported by a Senior Research Fellowship from CSIR (India). The Central Instrumentation Laboratory, University of Hyderabad is gratefully acknowledged for the use of the Jasco J-810 CD spectropolarimeter. We acknowledge the University Grants Commission (India) for their support through the UPE and CAS programs, to the University of Hyderabad and School of Chemistry, respectively.

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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  1. 1.School of ChemistryUniversity of HyderabadHyderabadIndia

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