Article ID Journal Published Year Pages File Type
1178383 Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics 2007 13 Pages PDF
Abstract

The napin from Brassica juncea, oriental mustard, is highly thermostable, proteolysis resistant and allergenic in nature. It consists of two subunits – one small (29 amino acid residues) and one large (86 amino acids residues) – held together by disulfide bonds. The thermal unfolding of napin has been followed by differential scanning calorimetry (DSC) and circular dichroism (CD) measurements. The thermal unfolding is characterized by a three state transition with TM1 and TM2 at 323.5 K and 335.8 K, respectively; ΔCP1 and ΔCP2 are 2.05 kcal mol− 1 K− 1 and 1.40 kcal mol− 1 K− 1, respectively. In the temperature range 310–318 K, the molecule undergoes dimerisation. Isothermal equilibrium unfolding by guanidinium hydrochloride also follows a three state transition, N ⇆ I ⇆ U with ΔG1H2O and ΔG2H2O values of 5.2 kcal mol− 1 and 5.1 kcal mol− 1 at 300 K, respectively. Excess heat capacity values obtained, are similar to those obtained from DSC measurements. There is an increase in hydrodynamic radius from 20 Å to 35.0 Å due to unfolding by guanidinium hydrochloride. In silico alignment of sequences of napin has revealed that the internal repeats (40%) spanning residues 31 to 60 and 73 to 109 are conserved in all Brassica species. The internal repeats may contribute to the greater stability of napin. A thorough understanding of the structure and stability of these proteins is essential before they can be exploited for genetic improvements for nutrition.

Related Topics
Physical Sciences and Engineering Chemistry Analytical Chemistry
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