Interaktion von MalY und Aes mit MalT, dem Transkriptionsaktivator des Maltosesystems von Escherichia coli

Abstract

The maltose system of Escherichia coli consists of 10 genes whose products are involved in the uptake and metabolism of maltose and maltodextrins. There are 3 known proteins directly interacting with the transcriptional activator MalT and stabilizing its inactive conformation: MalK, the ATP-hydrolyzing subunit of the system, MalY, a bC-S lyase, and Aes, an enzyme with acetyl esterase activity.The analysis of MalY mutants with reduced repressor ability and the X-ray structure allowed to determine a distiguished region on the surface of the protein representing the interaction site with MalT.Experiments with fragments of MalT showed that the N terminus of the protein is sufficient for the interaction with MalY but not with MalK.A series of MalT mutants cause elevated mal-gene expression compared to the wildtype protein in the absence of the known repressors and of exogenous maltodextrins. In the presence of the repressors none of the mutants is resistent against all of them, but they show different sensitivity patterns.In contrast to the in vivo results no increased expression of the mal-system was observed in transcription assays with one of the mutants. This could be explained by the existence of an hitherto unknown factor in the cell which represses MalT by direct interaction.It was not possible to clone fragments of Aes which have a repressing effect on MalT. It is conceivable that the site of interaction consists of residues distributed widely over the primary sequence.