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.
