Institute of Biochemistry, University of Cologne, Cologne, Germany.
J Bacteriol. 2013 Jun;195(11):2573-84. doi: 10.1128/JB.01629-12. Epub 2013 Mar 29.
The Gram-positive Corynebacterium glutamicum efficiently metabolizes maltose by a pathway involving maltodextrin and glucose formation by 4-α-glucanotransferase, glucose phosphorylation by glucose kinases, and maltodextrin degradation via maltodextrin phosphorylase and α-phosphoglucomutase. However, maltose uptake in C. glutamicum has not been investigated. Interestingly, the presence of maltose in the medium causes increased expression of ptsG in C. glutamicum by an unknown mechanism, although the ptsG-encoded glucose-specific EII permease of the phosphotransferase system itself is not required for maltose utilization. We identified the maltose uptake system as an ABC transporter encoded by musK (cg2708; ATPase subunit), musE (cg2705; substrate binding protein), musF (cg2704; permease), and musG (cg2703; permease) by combination of data obtained from characterization of maltose uptake and reanalyses of transcriptome data. Deletion of the mus gene cluster in C. glutamicum Δmus abolished maltose uptake and utilization. Northern blotting and reverse transcription-PCR experiments revealed that musK and musE are transcribed monocistronically, whereas musF and musG are part of an operon together with cg2701 (musI), which encodes a membrane protein of unknown function with no homologies to characterized proteins. Characterization of growth and [(14)C]maltose uptake in the musI insertion strain C. glutamicum IMcg2701 showed that musI encodes a novel essential component of the maltose ABC transporter of C. glutamicum. Finally, ptsG expression during cultivation on different carbon sources was analyzed in the maltose uptake-deficient strain C. glutamicum Δmus. Indeed, maltose uptake by the novel ABC transport system MusEFGK2I is required for the positive effect of maltose on ptsG expression in C. glutamicum.
革兰氏阳性棒状杆菌可通过 4-α-葡聚糖转移酶将麦芽糖转化为麦芽糊精和葡萄糖、葡萄糖激酶将葡萄糖磷酸化、以及通过麦芽糖磷酸化酶和α-磷酸葡萄糖变位酶降解麦芽糊精的途径有效代谢麦芽糖。然而，在谷氨酸棒杆菌中，麦芽糖的摄取尚未被研究过。有趣的是，尽管磷酸转移酶系统本身编码的葡萄糖特异性 EII 通透酶 ptsG 编码的葡萄糖特异性 EII 通透酶本身并不需要用于麦芽糖利用，但麦芽糖在培养基中的存在会导致谷氨酸棒杆菌中 ptsG 的表达增加，其机制未知。我们通过对麦芽糖摄取的特性进行描述并重新分析转录组数据，鉴定出麦芽糖摄取系统是由 musK（cg2708；ATP 酶亚基）、musE（cg2705；底物结合蛋白）、musF（cg2704；通透酶）和 musG（cg2703；通透酶）编码的 ABC 转运体。在谷氨酸棒杆菌 Δmus 中缺失 mus 基因簇会导致麦芽糖摄取和利用的丧失。Northern 印迹和反转录-PCR 实验表明，musK 和 musE 是单顺反子转录的，而 musF 和 musG 与 cg2701（musI）一起构成一个操纵子，该操纵子编码一种功能未知的膜蛋白，与已鉴定的蛋白无同源性。在插入突变株 C. glutamicum IMcg2701 中进行生长和 [(14)C]麦芽糖摄取的表征实验表明，musI 编码了谷氨酸棒杆菌麦芽糖 ABC 转运体的一个新的必需组成部分。最后，在缺乏麦芽糖摄取能力的菌株 C. glutamicum Δmus 中分析了在不同碳源上培养时 ptsG 的表达。事实上，新型 ABC 转运系统 MusEFGK2I 的麦芽糖摄取对于谷氨酸棒杆菌中麦芽糖对 ptsG 表达的正向作用是必需的。
