Aspergillus fumigatus is a filamentous fungus whose hyphae are divided into compartments by cross walls, known as septa. In this case, the term “cells” is not used, since adjacent compartments are connected via septal pores and thus, under normal growth conditions, share a continuous cytoplasm. External factors can cause damage to the hyphae, e.g., from immune cells or antifungal agents; this often results in damage to the cell wall, leading to lysis and the leakage of cytoplasm. If the pores cannot be quickly sealed in this situation, the entire hypha dies.
Aspergillus fumigatus is a filamentous fungus whose hyphae are divided into compartments by cross walls, known as septa. In this case, the term “cells” is not used, since adjacent compartments are connected via septal pores and thus, under normal growth conditions, share a continuous cytoplasm. External factors can cause damage to the hyphae, e.g., from immune cells or antifungal agents; this often results in damage to the cell wall, leading to lysis and the leakage of cytoplasm. If the pores cannot be quickly sealed in this situation, the entire hypha dies.
The ability to seal septal pores is therefore a key factor in the stress resistance and virulence of A. fumigatus. We now know that this fungus can employ two distinct mechanisms. Special organelles, called Woronin bodies, are anchored on both sides of the pore by the Lah protein. These organelles have a rigid structure, as their interior is filled with a paracrystalline matrix composed of the HexA protein. If a Woronin body is pushed into the pore by the cytoplasmic flow that occurs following injury, the pore closes permanently.
The second mechanism allows the fungus to reversibly close the pore and is based on the Spa proteins (septal pore-associated proteins). This protein family was first described in the model organism Neurospora crassa, where it comprises 18 proteins. We have identified orthologous proteins in A. fumigatus and are now attempting to elucidate their functions. Initial results show that Spa10 and Spa13 are of central importance for the pore apparatus and that Spa12 forms vesicle-like structures on both sides of the pore.
