Inhibits transcription of the trehalose/maltose transport gene cluster (malE operon) and of the maltodextrin transport gene cluster (mdxE operon). Acts by binding to two different operator sequences in both promoters, preventing polymerase recruitment and transcription. Repressor activity is regulated by binding of different sugars to TrmB. These sugars can act as inducers or corepressors. Binding of maltose and trehalose results in derepression of the malE operon, and binding of maltotriose, larger maltodextrins and, to a minor extent, sucrose results in derepression of the mdxE operon. In contrast, binding of glucose causes stronger repression of the malE and mdxE operons. Maltose may also act as a corepressor of the mdxE operon. Homodimer. Contains an N-terminal DNA-binding domain and a C-terminal sugar-binding domain. Belongs to the transcriptional regulator TrmB family.