Stability of Murraya koenigii miraculin-like protein in different physicochemical conditions

The Murraya koenigii miraculin-like protein (MKMLP) has been shown to have unusual solubility and stability properties. Here, the conformational stability and the solubility of MKMLP were assessed in different physicochemical conditions. In solubility studies, the presence of salt helped in resolubilization of precipitated protein at low pH. 8-Anilino-1-naphthalene sulfonate (ANS) fluorescence studies showed that protein significantly unfolds at pH 2.0 and addition of salts helped in refolding of the protein with a recovery of inhibitory activity. In the presence of DTT, a substantial increase in ANS fluorescence was observed only when protein was incubated for more than 30 min in 100-mM DTT. MKMLP retained approximately 52% of inhibitory activity when incubated for 120 min in 100-mM DTT. A minor increase in fluorescence intensity was observed in presence of urea and guanidine hydrochloride, however, a significant amount of unfolding was observed in presence of high concentration of beta-mercaptoethanol, SDS, and HCl.