Adapting protein solubility by glycosylation.: N-Glycosylation mutants of Coprinus cinereus peroxidase in salt and organic solutions

Abstract

Protein solubility is a fundamental parameter in biology and biotechnology. In the present study we have constructed and analyzed five mutants of Coprinus cinereus peroxidase (CIP) with 0, 1, 2, 4 and 6 N-glycosylation sites. All mutants contain Man x(GlcNAc) 2 glycans. The peroxidase activity was the same for wild-type CIP and all the glycosylation mutants when measured with the large substrate 2,2′-azino-bis(-3-ethylbenzthiazoline-6-sulfonic acid). The solubility of the five CIP mutants showed a linear dependence on the number of carbohydrate residues attached to the protein in buffered solution of both ammonium sulfate (AMS) and acetone, increasing in AMS and decreasing in acetone. Moreover, the change in free energy of solvation appears to be a constant, though with opposite signs in these solvents, giving ΔΔ G° sol=−0.32±0.05 kJ/mol per carbohydrate residue in 2.0 M AMS, a value previously obtained comparing ordinary and deglycosylated horseradish peroxidase, and 0.37±0.10 kJ/mol in 60 v/v% acetone.