Attributes of glycosylation in the establishment of the unfolding pathway of Soybean Agglutinin
Sharmistha Sinha 1 and Avadhesha Surolia 2*
1 Molecular Biophysics Unit, Indian Institute of Science
2 National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi-110067, India
* To whom correspondence should be addressed. E-mail: surolia{at}nii.res.in.
Submitted on July 3, 2006
Revised on July 24, 2006
Accepted on 29 August 2006
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Abstract |
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Soybean agglutinin (gSBA) is a tetrameric legume lectin each of whose subunits are glycosylated. Earlier studies have shown that this protein shows exceptionally high stability in terms of free energy of unfolding when compared to other proteins from the same family (Sinha et al. 2005). This article deals with the unfolding reactions of the non-glycosylated recombinant form of the protein rSBA and its comparison with the glycosylated counterpart gSBA. The non-glycosylated form features a lower stability when compared to the glycosylated form. Further the unfolding pathways in the two are widely different. While the glycosylated form undergoes a simple two state unfolding, the non-glycosylated species unfolds via a compact monomeric intermediate which is not a molten globule. Representative isothermal and thermal denaturation profiles show that glycosylation accounts for a stabilization of nearly 9 kcal/mol of the tetramer, while the difference in Tm in the two forms is 26°C. Computational studies on the glycan-protein interactions at the non-canonical interface of the protein show that quite a number of hydrogen bonding and hydrophobic interactions stabilize the glycoprotein tetramer.
Key Words:
Denaturation, Glycosylation, Inter-subunit interactions, Oligomannose, Soybean agglutinin, Stability
