Graduate School of Agriculture, Kyoto University, Kitashirakawaoiwakecho, Sakyo-ku, Kyoto 606-8502, Japan.
Lett Appl Microbiol. 2023 Apr 3;76(4). doi: 10.1093/lambio/ovad048.
Hydrophobins are small-secreted proteins comprising both hydrophobic and hydrophilic parts, that can self-assemble into an amphiphilic film at the air-liquid interface. More than 20 hydrophobin genes have been estimated in the white-rot fungus Pleurotus ostreatus. In our previous studies, three hydrophobin genes were shown to be predominantly expressed under ligninolytic conditions, and only vmh3 was downregulated in both the delignification-deficient mutant Δgat1 and Δhir1 strains. Here, we focused on the function of the hydrophobin Vmh3 to clarify its physiological role in lignin degradation. When the hyphae were observed by transmission electron microscopy, deletion of vmh3 resulted in the disappearance of black aggregates at the interface between the cell wall and outer environment. Deletion of vmh3 resulted in reduced hydrophobicity when 0.2% sodium dodecyl sulfate was dropped onto the mycelial surface. These results suggest that Vmh3 functions on the cell surface and plays a major role in mycelial hydrophobization. Furthermore, the Δvmh3 strain showed a marked delay in lignin degradation on beech wood sawdust medium, while the production of lignin-modifying enzymes was not reduced. This study demonstrated, for the first time, the possible effect of hydrophobin on lignin degradation by a white-rot fungus.
水孔蛋白是由疏水和亲水部分组成的小分泌蛋白，可在气液界面自组装成两亲性膜。白腐菌糙皮侧耳中估计有超过 20 个水孔蛋白基因。在我们之前的研究中，发现三个水孔蛋白基因在木质素降解条件下主要表达，而在木质素脱除缺陷突变株Δ gat1 和Δ hir1 中，只有 vmh3 下调。在这里，我们专注于水孔蛋白 Vmh3 的功能，以阐明其在木质素降解中的生理作用。当通过透射电子显微镜观察菌丝体时，vmh3 的缺失导致细胞壁和外环境之间界面处的黑色聚集体消失。当 0.2%十二烷基硫酸钠滴到菌丝体表面时，vmh3 的缺失导致疏水性降低。这些结果表明 Vmh3 在细胞表面起作用，并在菌丝体疏水性方面起主要作用。此外，Δ vmh3 菌株在山毛榉木屑培养基上木质素降解明显延迟，而木质素修饰酶的产生并未减少。这项研究首次证明了水孔蛋白可能对白腐菌木质素降解的影响。
