Deletion of <i>admB</i> gene encoding a fungal ADAM affects cell wall construction in <i>Aspergillus oryzae</i>

Mammals possess a unique signaling system based on the proteolytic mechanism of a disintegrin and metalloproteinases (ADAMs) on the cell surface. We found two genes encoding ADAMs in <i>Aspergillus oryzae</i> and named them <i>admA</i> and <i>admB</i>. We produced <i>admA</i> and <i>admB</i> deletion strains to elucidate their biological function and clarify whether fungal ADAMs play a similar role as in mammals. The <i>∆admA∆admB</i> and <i>∆admB</i> strains were sensitive to cell wall-perturbing agents, congo red, and calcofluor white. Moreover, the two strains showed significantly increased weights of total alkali-soluble fractions from the mycelial cell wall compared to the control strain. Furthermore, <i>∆admB</i> showed MpkA phosphorylation at lower concentration of congo red stimulation than the control strain. However, the MpkA phosphorylation level was not different between <i>∆admB</i> and the control strain without the stimulation. The results indicated that <i>A. oryzae</i> AdmB involved in the cell wall integrity without going through the MpkA pathway.哺乳动物拥有一套基于细胞表面解整合素金属蛋白酶（ADAMs，disintegrin and metalloproteinases）蛋白水解机制的独特信号系统。我们在米曲霉（Aspergillus oryzae）中发现了两个编码ADAMs的基因，并将其命名为admA与admB。为阐明二者的生物学功能，并厘清真菌ADAMs是否发挥与哺乳动物中类似的作用，我们构建了admA与admB的基因缺失菌株。实验结果显示，∆admA∆admB与∆admB菌株对细胞壁扰动剂刚果红、卡尔科弗卢尔白敏感。此外，相较于对照菌株，这两株缺失菌株的菌丝细胞壁总碱可溶性组分的重量显著升高。进一步实验发现，相较于对照菌株，∆admB菌株在更低浓度的刚果红刺激下即可检测到MpkA磷酸化；但在无刺激条件下，∆admB菌株与对照菌株的MpkA磷酸化水平并无显著差异。综上，研究结果表明，米曲霉（A. oryzae）的AdmB可不依赖MpkA通路参与细胞壁完整性的调控。