Welte W: Crystal structure of the sugar binding domain of the archaeal transcriptional regulator TrmB

TrmB is an -glucoside-sensing transcriptional regulator con-trolling two operons encoding maltose/trehalose and maltodextrin ABC transporters ofPyrococcus furiosus. The crystal structure of an N-terminal truncated derivative of TrmB (amino acids 2–109 delet-ed; TrmB2–109) was solved at 1.5 A ̊ resolution. This protein has lost its DNA binding domain but has retained its sugar recognition site. The structure represents a novel sugar-binding fold. TrmB2–109 boundmaltose, glucose, sucrose, andmaltotriose, exhibitingKd val-ues of 6.8, 25, 34, and 160 M, respectively. TrmB2–109 behaved as a monomer in dilute buffer solution in contrast to the full-length protein, which is a dimer. Co-crystallization with bound maltose identified a binding site involving seven amino acid residues: Ser229, Asn305, Gly320, Met321, Val324, Ile325, and Glu326. Six of these resi-dues interact with the nonreducing glucosyl residue ofmaltose. The nonreducing glucosyl residue is shared by all substrates bound t