Toxic misfolding of Arabidopsis cellulases in the secretory pathway of Pichia pastoris

► Two plant cellulases were expressed in the secretory pathway of Pichia pastoris. ► Misfolding of these enzymes was toxic, causing strong activation of the unfolded protein response and extensive cell lysis. ► The catalytic domain of one modular cellulase folded correctly when expressed at low temperature. ► A sensitive biomarker for Pichia cell lysis is described.