The reversible two-state unfolding of a monocot mannose-binding lectin from garlic bulbs reveals the dominant role of the dimeric interface in its stabilization.


Abstract

Allium sativum agglutinin (ASAI) is a heterodimeric mannose-specific bulb lectin possessing two polypeptide chains of molecular mass 11.5 and 12.5 kDa. The thermal unfolding of ASAI, characterized by differential scanning calorimetry and circular dichroism, shows it to be highly reversible and can be defined as a two-state process in which the folded dimer is converted directly to the unfolded monomers (A2 if 2U). Its conformational stability has been determined as a function of temperature, GdnCl concentration, and pH using a combination of thermal and isothermal GdnCl-induced unfolding monitored by DSC, far-UV CD, and fluorescence, respectively. Analyses of these data yielded the heat capacity change upon unfolding (DeltaC(p) and also the temperature dependence of the thermodynamic parameters, namely, DeltaG, DeltaH, and DeltaS. The fit of the stability curve to the modified Gibbs-Helmholtz equation provides an estimate of the thermodynamic parameters DeltaH(g), DeltaS(g), and DeltaC(p) as 174.1 kcal x mol(-1), 0.512 kcal x mol(-1) x K(-1), and 3.41 kcal x mol(-1) x K(-1), respectively, at T(g) = 339.4 K. Also, the free energy of unfolding, DeltaG(s), at its temperature of maximum stability (T(s) = 293 K) is 13.13 kcal x mol(-1). Unlike most oligomeric proteins studied so far, the lectin shows excellent agreement between the experimentally determined DeltaC(p) (3.2 +/- 0.28 kcal x mol(-1) x K(-1)) and those evaluated from a calculation of its accessible surface area. This in turn suggests that the protein attains a completely unfolded state irrespective of the method of denaturation. The absence of any folding intermediates suggests the quaternary interactions to be the major contributor to the conformational stability of the protein, which correlates well with its X-ray structure. The small DeltaC(p) for the unfolding of ASAI reflects a relatively small, buried hydrophobic core in the folded dimeric protein. Study holds ProTherm entries: 11491, 11492, 11493, 11494, 11495, 11496, 11497, 11498, 11499, 11500, 11501, 11502, 11503, 11504, 11505, 11506, 11507, 11508, 11509, 11510, 11511, 11512, 11513, 11514, 11515, 11516, 11517, 11518, 11519, 11520 Extra Details: Tm is the temperature at which dGt=0 two-state process; conformational stability; accessible surface area;,quaternary interactions; hydrophobic core

Submission Details

ID: iQDt4U643

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:42 p.m.

Version: 1

Publication Details
Bachhawat K;Kapoor M;Dam TK;Surolia A,Biochemistry (2001) The reversible two-state unfolding of a monocot mannose-binding lectin from garlic bulbs reveals the dominant role of the dimeric interface in its stabilization. PMID:11401577
Additional Information

Number of data points 74
Proteins Mannose-specific lectin ; lectin I
Unique complexes 1
Assays/Quantities/Protocols Experimental Assay: Cm temp:323 K ; Experimental Assay: m temp:323 K ; Experimental Assay: dG_H2O temp:323 K ; Experimental Assay: Cm temp:318 K ; Experimental Assay: m temp:318 K ; Experimental Assay: dG_H2O temp:318 K ; Experimental Assay: Cm temp:313 K ; Experimental Assay: m temp:313 K ; Experimental Assay: dG_H2O temp:313 K ; Experimental Assay: Cm temp:308 K ; Experimental Assay: m temp:308 K ; Experimental Assay: dG_H2O temp:308 K ; Experimental Assay: Cm temp:303 K ; Experimental Assay: m temp:303 K ; Experimental Assay: dG_H2O temp:303 K ; Experimental Assay: Cm temp:298 K ; Experimental Assay: m temp:298 K ; Experimental Assay: dG_H2O temp:298 K ; Experimental Assay: Cm temp:293 K ; Experimental Assay: m temp:293 K ; Experimental Assay: dG_H2O temp:293 K ; Experimental Assay: Cm temp:288 K ; Experimental Assay: m temp:288 K ; Experimental Assay: dG_H2O temp:288 K ; Experimental Assay: Cm temp:283 K ; Experimental Assay: m temp:283 K ; Experimental Assay: dG_H2O temp:283 K ; Experimental Assay: dCp temp:323.7 K ; Experimental Assay: dHvH temp:323.7 K, prot_conc:- ; Experimental Assay: dCp temp:326.3 K ; Experimental Assay: dHvH temp:326.3 K, prot_conc:- ; Experimental Assay: dCp temp:328.7 K ; Experimental Assay: dHvH temp:328.7 K, prot_conc:- ; Experimental Assay: dCp temp:329.3 K ; Experimental Assay: dHvH temp:329.3 K, prot_conc:- ; Experimental Assay: dCp temp:333.8 K ; Experimental Assay: dHvH temp:333.8 K, prot_conc:- ; Experimental Assay: dCp temp:337.2 K ; Experimental Assay: dHvH temp:337.2 K, prot_conc:- ; Experimental Assay: dCp temp:339.4 K ; Experimental Assay: dHvH temp:339.4 K, prot_conc:- ; Experimental Assay: Tm pH:8.0, prot_conc:32 micro M ; Experimental Assay: dHvH pH:8.0, prot_conc:32 micro M ; Experimental Assay: Tm pH:7.5, prot_conc:32 micro M ; Experimental Assay: dHvH prot_conc:32 micro M ; Experimental Assay: Tm pH:7.0, prot_conc:32 micro M ; Experimental Assay: dHvH pH:7.0, prot_conc:32 micro M ; Experimental Assay: Tm pH:6.5, buffers:citrate phosphate: 20 mM, prot_conc:32 micro M ; Experimental Assay: dHvH pH:6.5, buffers:citrate phosphate: 20 mM, prot_conc:32 micro M ; Experimental Assay: Tm pH:6.2, buffers:citrate phosphate: 20 mM, prot_conc:32 micro M ; Experimental Assay: dHvH pH:6.2, buffers:citrate phosphate: 20 mM, prot_conc:32 micro M ; Experimental Assay: Tm pH:6.0, buffers:citrate phosphate: 20 mM, prot_conc:32 micro M ; Experimental Assay: dHvH pH:6.0, buffers:citrate phosphate: 20 mM, prot_conc:32 micro M ; Experimental Assay: Tm pH:5.8, buffers:citrate phosphate: 20 mM, prot_conc:32 micro M ; Experimental Assay: dHvH pH:5.8, buffers:citrate phosphate: 20 mM, prot_conc:32 micro M ; Experimental Assay: Tm pH:5.5, buffers:citrate phosphate: 20 mM, prot_conc:32 micro M ; Experimental Assay: dHvH pH:5.5, buffers:citrate phosphate: 20 mM, prot_conc:32 micro M ; Experimental Assay: Tm pH:5.0, buffers:citrate phosphate: 20 mM, prot_conc:32 micro M ; Experimental Assay: dHvH pH:5.0, buffers:citrate phosphate: 20 mM, prot_conc:32 micro M ; Experimental Assay: dHcal prot_conc:64.0 micro M ; Experimental Assay: Tm pH:7.5, prot_conc:64.0 micro M ; Experimental Assay: dHvH prot_conc:64.0 micro M ; Experimental Assay: dHcal prot_conc:32.0 micro M ; Experimental Assay: Tm pH:7.5, prot_conc:32.0 micro M ; Experimental Assay: dHvH prot_conc:32.0 micro M ; Experimental Assay: dHcal prot_conc:16.0 micro M ; Experimental Assay: Tm pH:7.5, prot_conc:16.0 micro M ; Experimental Assay: dHvH prot_conc:16.0 micro M ; Experimental Assay: dHcal prot_conc:8.0 micro M ; Experimental Assay: Tm pH:7.5, prot_conc:8.0 micro M ; Experimental Assay: dHvH prot_conc:8.0 micro M ; Experimental Assay: dHcal prot_conc:4.0 micro M ; Experimental Assay: Tm pH:7.5, prot_conc:4.0 micro M ; Experimental Assay: dHvH prot_conc:4.0 micro M
Libraries Mutations for sequence A:RNLLTNGEGLYAGQSLDVEPYHFIMQEDCNLVLYDHSTSVWASNTGILGKKGCKAVLQSDGNFVVYDAEGRSLWASHSVRGNGNYVLVLQEDGNVVIYGSDIWSTGTYK/D:RNILMNDEGLYAGQSLDVEPYHLIMQEDCNLVLYDHSTAVWTTNTDIPGKKGCKAVLQSDGNFVVYDAEGRSLWASHSVRGNGNYVLVLQEDGNVVIYGSDIWSTNTYK/P:RNLLTNGEGLYAGQSLDVEPYHFIMQEDCNLVLYDHSTSVWASNTGILGKKGCKAVLQSDGNFVVYDAEGRSLWASHSVRGNGNYVLVLQEDGNVVIYGSDIWSTGTYK/Q:RNILMNDEGLYAGQSLDVEPYHLIMQEDCNLVLYDHSTAVWTTNTDIPGKKGCKAVLQSDGNFVVYDAEGRSLWASHSVRGNGNYVLVLQEDGNVVIYGSDIWSTNTYK
Sequence Assay Result Units