Heterologous expression of peptidyl-Lys metallopeptidase of Armillaria mellea and mutagenic analysis of the recombinant peptidase

Abstract

A method to express, purify and modify the Peptidyl-Lys metallopeptidase (LysN) of Armillaria mellea in Pichia pastoris was developed to enable functional studies of the protease. Based on prior work, we propose a mechanism of action of LysN. Catalytic residues were investigated by site-directed mutagenesis. As anticipated, these mutations resulted in significantly reduced catalytic rates. Additionally, based on molecular modelling eleven mutants were designed to have altered substrate specificity. The S1′ binding pocket of LysN is quite narrow and lined with negative charge to specifically accommodate lysine. To allow for arginine specificity in S1′, it was proposed to extend the S1′ binding pocket by mutagenesis, however the resulting mutant did not show any activity with arginine in P1′. Two mutants, A101D and T105D, showed increased specificity towards arginine in subsites S2′-S4′ compared to the wild type protease. We speculate that the increased specificity to result from the additional negative charge which attract and interact with positively charged residues better than the wild type.