Global transcriptional repressor of the maltodextrin transport gene cluster (mdxE operon) and most likely of all genes encoding glycolytic enzymes. Acts by binding to the conserved TGM (Thermococcales-Glycolytic-Motif) sequences in their promoter region. Can also interact with non-TGM sequences. Repressor activity is regulated by binding of different sugars to TrmBL1. Binding of maltose and maltotriose results in derepression of the target genes. However, high sugar concentration results in formation of octamers with high affinity for DNA, which may prevent transcription of target genes. Homotetramer. Forms homooctamers in the presence of maltotriose or maltose. Autoregulated. Contains an N-terminal DNA-binding domain and a C-terminal sugar-binding domain. Belongs to the transcriptional regulator TrmB family.