Characterization of a second physiologically relevant lactose permease gene (lacpB) in Aspergillus nidulans
Characterization of a second physiologically relevant lactose permease gene (lacpB) in Aspergillus nidulans
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DOI：
10.1099/mic.0.000267
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发表时间：
2016-05-01
期刊：
影响因子：
2.8
通讯作者：
Karaffa, Levente
中科院分区：
文献类型：
--
作者：
Fekete, Erzsebet;Orosz, Anita;Karaffa, Levente
在构巢曲霉中，乳糖分解代谢的限速步骤是摄取而不是水解。乳糖通透酶 A 编码基因 (lacpA) 的缺失会降低乳糖的生长速度，而其过表达则能够比野生型菌株生长得更快。我们已经确定了第二种生理相关的乳糖转运蛋白 LacpB。来自lacpB删除突变体的甘油生长的菌丝体似乎在培养基转移后的前60小时内仅吸收微量的乳糖，而双lacpA/lacpB删除菌株的菌丝体无法从乳糖产生新的生物量。尽管两种 lacp 基因的转录均受到乳糖的强烈诱导，但它们的诱导物谱却显着不同。 D-半乳糖培养物中 lacpA 表达较高，但 lacpB 表达较高。然而，lacpB 也对 β 连接的吡喃葡萄糖二聚体纤维二糖和槐糖产生强烈反应，而这些纤维素分解系统的诱导剂不会引起任何 lacpA 反应。然而，在缺乏lacpA基因的菌株中，与野生型背景相比，lacpB转录物在纤维二糖上被诱导至更高水平。事实上，lacpA 删除体中纤维二糖的吸收更快，生物量形成加速。相反，在lacpB敲除菌株中，生长速率和纤维二糖摄取相对于野生型显着降低，表明纤维素和乳糖分解代谢系统采用共同的元素。尽管如此，我们的通透酶突变体仍然在纤维二糖上生长，这表明构巢曲霉中的纤维二糖摄取主要涉及迄今为止未知的运输系统。
In Aspergillus nidulans, uptake rather than hydrolysis is the rate-limiting step of lactose catabolism. Deletion of the lactose permease A-encoding gene (lacpA) reduces the growth rate on lactose, while its overexpression enables faster growth than wild-type strains are capable of. We have identified a second physiologically relevant lactose transporter, LacpB. Glycerol-grown mycelia from mutants deleted for lacpB appear to take up only minute amounts of lactose during the first 60 h after a medium transfer, while mycelia of double lacpA/lacpB-deletant strains are unable to produce new biomass from lactose. Although transcription of both lacp genes was strongly induced by lactose, their inducer profiles differ markedly. lacpA but not lacpB expression was high in D-galactose cultures. However, lacpB responded strongly also to beta-linked glucopyranose dimers cellobiose and sophorose, while these inducers of the cellulolytic system did not provoke any lacpA response. Nevertheless, lacpB transcript was induced to higher levels on cellobiose in strains that lack the lacpA gene than in a wild-type background. Indeed, cellobiose uptake was faster and biomass formation accelerated in lacpA deletants. In contrast, in lacpB knockout strains, growth rate and cellobiose uptake were considerably reduced relative to wild-type, indicating that the cellulose and lactose catabolic systems employ common elements. Nevertheless, our permease mutants still grew on cellobiose, which suggests that its uptake in A. nidulans prominently involves hitherto unknown transport systems.