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Acid trehalase in yeasts and filamentous fungi: localization, regulation and physiological function

机译:酵母和丝状真菌中的酸性海藻糖酶:定位,调节和生理功能。

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Yeasts and filamentous fungi are endowed with two different trehalose-hydrolysing activities, termed acid and neutral trehalases according to their optimal pH for enzymatic activity. A wealth of information already exists on fungal neutral trehalases, while data on localization, regulation and function of fungal acid trehalases have remained elusive. The gene encoding the latter enzyme has now been isolated from two yeast species and two filamentous fungi, and sequences encoding putative acid trehalase can be retrieved from available public sequences. Despite weak similarities between amino acids sequences, this type of trehalase potentially harbours either a transmembrane segment or a signal peptide at the N-terminal sequence, as deduced from domain prediction algorithms. This feature, together with the demonstration that acid trehalase from yeasts and filamentous fungi is localized at the cell surface, is consistent with its main role in the utilisation of exogenous trehalose as a carbon source. The growth on this disaccharide is in fact pretty effective in most fungi except in Saccharomyces cerevisiae. This yeast species actually exhibits a "Kluyver effect" on trehalose. Moreover, an oscillatory behaviour reminiscent of what is observed in aerobic glucose-limited continuous cultures at low dilution rate is also observed in batch growth on trehalose. Finally, the S. cerevisiae acid trehalase may also participate in the catabolism of endogenous trehalose by a mechanism that likely requires the export of the disaccharide, its extracellular hydrolysis, and the subsequent uptake of the glucose released. Based on these recent findings, we suggest to rename "acid" and "neutral" trehalases as "extracellular" and "cytosolic" trehalases, which is more adequate to describe their localization and function in the fungal cell.
机译:酵母和丝状真菌具有两种不同的海藻糖水解活性,根据其酶促活性的最佳pH值称为酸和中性海藻糖酶。关于真菌中性海藻糖酶的信息已经很多,而有关真菌酸性海藻糖酶的定位,调控和功能的数据仍然难以捉摸。现在已经从两种酵母菌和两种丝状真菌中分离出了编码后者酶的基因,并且可以从可获得的公共序列中检索出编码推定的酸性海藻糖酶的序列。尽管氨基酸序列之间的相似性较弱,但根据域预测算法推论,这种类型的海藻糖酶可能在N端序列处具有跨膜片段或信号肽。此功能以及来自酵母和丝状真菌的酸性海藻糖酶位于细胞表面的证明,与其在利用外源海藻糖作为碳源中的主要作用相吻合。实际上,除了酿酒酵母以外,这种二糖的生长在大多数真菌中都非常有效。该酵母实际上对海藻糖表现出“克鲁维效应”。此外,在海藻糖上分批生长中还观察到振荡行为,其回想起在低稀释率下有氧葡萄糖受限的连续培养物中观察到的振荡行为。最后,酿酒酵母酸海藻糖酶也可能通过一种机制参与内源性海藻糖的分解代谢,该机制可能需要二糖的输出,其胞外水解以及随后吸收的葡萄糖的吸收。基于这些最新发现,我们建议将“酸”和“中性”海藻糖酶重命名为“细胞外”和“胞质”海藻糖酶,这样更足以描述它们在真菌细胞中的定位和功能。

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