The DAHL (Double All-Helical Ligand-binding) domain is a novel periplasmic sensory domain, which is found in major types of bacterial signal transduction proteins: histidine kinases and diguanylate cyclases/phosphodiesterases, and, occasionally in chemoreceptors. The majority of the DAHL domain-containing proteins were found in alpha-, beta-, gamma- and epsilonproteobacteria. It is also present in some cyanobacterial species. Secondary structure prediction suggested that DAHL consists predominantly of alpha-helical regions. The DAHL domain was identified in the Tlp10 chemoreceptor from the human pathogen Campylobacter jejuni and in the VirA sensor histidine kinase from a plant pathogen Agrobacterium tumefaciens [1]. This domain recognises Asp, Ile, purine, fumarate, malate, alpha-ketoglutarate, mannose, rhamnose, fucose, sialic acid, Arg, thiamine and galactose (Matilla et al., FEMS Microbiology Reviews, fuab043, 45, 2021, 1 https://doi.org/10.1093/femsre/fuab043).

1: The Campylobacter jejuni chemoreceptor Tlp10 has a bimodal ligand-binding domain and specificity for multiple classes of chemoeffectors. Elgamoudi BA, Andrianova EP, Shewell LK, Day CJ, King RM, Taha, Rahman H, Hartley-Tassell LE, Zhulin IB, Korolik V; Sci Signal. 2021; [Epub ahead of print] PMID:33402336