Unfolding studies on soybean agglutinin and concanavalin a tetramers: a comparative account.
The unfolding pathway of two very similar tetrameric legume lectins soybean agglutinin (SBA) and Concanavalin A (ConA) were determined using GdnCl-induced denaturation. Both proteins displayed a reversible two-state unfolding mechanism. The analysis of isothermal denaturation data provided values for conformational stability of the two proteins. It was found that the DeltaG of unfolding of SBA was much higher than ConA at all the temperatures at which the experiments were done. ConA had a T(g) 18 degrees C less than SBA. The higher conformational stability of SBA in comparison to ConA is largely due to substantial differences in their degrees of subunit interactions. Ionic interactions at the interface of the two proteins especially at the noncanonical interface seem to play a significant role in the observed stability differences between these two proteins. Furthermore, SBA is a glycoprotein with a GlcNac2Man9 chain attached to Asn-75 of each subunit. The sugar chain in SBA lies at the noncanonical interface of the protein, and it is found to interact with the amino acid residues in the adjacent noncanonical interface. These interactions further stabilize SBA with respect to ConA, which is not glycosylated.
Sinha
Sharmistha
S
Molecular Biophysics Unit, Indian Institute of Science, Bangalore-560012, India.
Mitra
Nivedita
N
Kumar
Gyanendra
G
Bajaj
Kanika
K
Surolia
Avadhesha
A
D000373:Agglutinins / Q000032:analysis / Q000737:chemistry*; D001665:Binding Sites; D032449:Canavalia / Q000378:metabolism*; D003198:Computer Simulation; D003208:Concanavalin A / Q000032:analysis / Q000737:chemistry*; D019281:Dimerization; D019791:Guanidine / Q000737:chemistry; D008956:Models, Chemical; D046912:Multiprotein Complexes / Q000032:analysis / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D011489:Protein Denaturation; D013025:Glycine max / Q000378:metabolism*; D013329:Structure-Activity Relationship
D000373:Agglutinins; D046912:Multiprotein Complexes; D003208:Concanavalin A; D019791:Guanidine