Lee I H, Walline R G, Plamann M
Department of Biology, Texas A&M University, College Station 77843-3258, USA.
Mol Microbiol. 1998 Jul;29(1):209-18. doi: 10.1046/j.1365-2958.1998.00923.x.
Protein secretion in filamentous fungi has been shown to be restricted to actively growing hyphal tips. To determine whether an increase in the amount f growing surface area of a fungus can lead to an increase in the amount of protein secretion, we examined secretion in a temperature-sensitive Neurospora crassa mcb mutant that shows a loss of growth polarity when incubated at restrictive temperature. Incubation of the mcb mutant at restrictive temperature results in a three- to fivefold increase in the level of extracellular protein and a 20-fold increase in carboxymethyl cellulase activity relative to a wild-type strain. A mutation in the cr-1 gene has been shown previously to suppress the apolar growth phenotype of the mcb mutant, and we find that the level of extracellular protein produced by a mcb; cr-1 double mutant was reduced to that of the wild-type control. Immunolocalization of a secreted endoglucanase revealed that proteins are secreted mainly at hyphal tips in hyphae exhibiting polar growth and over the entire surface area of bulbous regions of hyphae that are produced after a shift of the mcb mutant to restrictive temperature. These results support the hypothesis that secretion of extracellular protein by a filamentous fungus can be significantly increased by mutations that alter growth polarity.
丝状真菌中的蛋白质分泌已被证明仅限于活跃生长的菌丝尖端。为了确定真菌生长表面积的增加是否会导致蛋白质分泌量的增加，我们检测了一种温度敏感型粗糙脉孢菌mcb突变体的分泌情况，该突变体在限制温度下培养时会丧失生长极性。相对于野生型菌株，在限制温度下培养mcb突变体导致细胞外蛋白质水平增加三到五倍，羧甲基纤维素酶活性增加20倍。先前已证明cr-1基因的突变可抑制mcb突变体的无极性生长表型，并且我们发现mcb;cr-1双突变体产生的细胞外蛋白质水平降低至野生型对照的水平。对一种分泌的内切葡聚糖酶进行免疫定位显示，在表现出极性生长的菌丝中，蛋白质主要在菌丝尖端分泌，而在mcb突变体转移至限制温度后产生的菌丝球茎区域的整个表面积上也有分泌。这些结果支持了这样一种假说，即丝状真菌中细胞外蛋白质的分泌可通过改变生长极性的突变而显著增加。
