Protein secretion in filamentous fungi--trying to understand a highly productive black box

Protein secretion is important in all fungi. The majority of proteins by fungi are thought to be glycosylated and many of them are structurally associated with the cell envelope, the plasma membrane and the cell wall. Many of the enzymes secreted by fungi have been incorporated into commercial processes and used in a range of industries. The existence of strains producing very high levels of secreted enzymes stimulated interest in the use of fungi as hosts for the expression of recombinant proteins. Despite the attention that protein secretion in fungi has attracted, and the multifaceted importance of the process, our understanding of the cellular mechanisms involved is still minimal and, for the most part, it is necessary to extrapolate from other eukaryotic organisms. However, current research suggests that protein secretion in filamentous fungi is intimately associated with the process of growth at the hyphal tip. Such unique features merit a detailed study of this important phenomenon.