Altered N-glycan processing in Trichoderma reesei affects the morphogenesis and improves the degradation of lignocellulose

Abstract:

[Background] Aspergillus fumigatus α-1,2-mannosidase MsdS is an enzyme that cleaves N-linked Man₈GlcNAc₂ in Golgi apparatus to produce Man₆GlcNAc₂ on mature secreted glycoproteins. MsdS has been shown to play a significant role in morphogenesis, cell wall synthesis and protein secretion in A. fumi gatus. Unlike A. fumigatus, Trichoderma reesei produces Man₈GlcNAc₂ on its mature secreted glycoproteins and grows normally. These observations suggest a species-specific N-glycan processing in filamentous fungi, however, its biological significance keeps unclear. [Objective] To evaluate the effects of the N-glycan processing on cell growth and protein secretion in T. reesei, A. fumigatus MsdS was introduced into T. reesei to change the glycoform on mature secreted proteins. [Methods] The recombinant plasmid haboring the msdS gene was constructed and transformed into T. reesei to obtain the msdS-expressing strain Tr-MsdS. The phenotypes, N-glycome, protein secretory pathway and cellulase activity were analysed. [Results] The msdS-expressing strain Tr-MsdS produced a major glycoform of Man₆GlcNAc₂ on its secreted glycoproteins, instead of Man₈GlcNAc₂ in the parent strain. Although the cell wall content of msdS-expressing strain Tr-MsdS was changed, it appeared that the cell wall integrity was not affected. However, phenotypes such as increased conidiation, multiple budding and random branching were observed in strain Tr-MsdS. In addition, expression of MsdS in T. ressei also affected protein secretion and increased the acivities of cellulose and β-mannan degradation by 9.9% and 32.2% at 50℃, respectively. [Conclusion] Our results indicate that the N-glycan processing plays an important role in protein secretion in T. reesei, especially cellulases. Also, our results provide a new strategy to improve cellulases production by interfering the N-glycan processing in T. reesei.