Effect of N-linked glycosylation on the activity and stability of a β-glucosidase from Putranjiva roxburghii

Abstract

In this study, the effect of N-glycosylation on the conformational and functional stability of Putranjiva roxburghii family 1 β-glucosidase (PRGH1) enzyme was investigated. The deglycosylation of PRGH1 was carried out by using PNGase F enzyme and confirmed by SDS-PAGE and carbohydrate estimation. Comparative analysis with respect to enzyme activity, stability and aggregation behaviour was carried out for the glycosylated and deglycosylated PRGH1. The deglycosylation of PRGH1 affected enzyme activity to a certain extent only where Km was not affected but a slight reduction in Vmax for various substrates was observed. Circular dichroism, fluorescence studies and differential scanning calorimetry (DSC) analysis demonstrated the possible effect of glycosylation on local and/or global conformational dynamics of protein and its effect on the thermostability of PRGH1. DSC results showed deglycosylated form had lower Tm as compared to the glycosylated form of PRGH1. The PRGH1 was found to be more sensitive to proteolysis after deglycosylation suggesting that the glycosylated PRGH1 was quite compact and rigid. Mutagenesis studies revealed that out of seven potential N-linked glycosylation sites, only three were glycosylated. The results demonstrated that N-linked glycosylation played an important role in conformational stability of PRGH1; however, it did not affect the enzyme function drastically.