Crystal structure of the sugar binding domain of the archaeal transcriptional regulator TrmB

Abstract

TrmB is an α-glucoside-sensing transcriptional regulator controlling two operons encoding maltose/trehalose and maltodextrin ABC transporters of Pyrococcus furiosus. The crystal structure of an N-terminal truncated derivative of TrmB (amino acids 2-109 deleted; TrmBΔ2-109) was solved at 1.5 Å resolution. This protein has lost its DNA binding domain but has retained its sugar recognition site. The structure represents a novel sugar-binding fold. TrmBΔ2-109 bound maltose, glucose, sucrose, and maltotriose, exhibiting Kd values of 6.8, 25, 34, and 160 μM, respectively. TrmBΔ2-109 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 residues interact with the nonreducing glucosyl residue of maltose. The nonreducing glucosyl residue is shared by all substrates bound to TrmB, suggesting it as a common recognition motif. © 2006 by The American Society for Biochemistry and Molecular Biology, Inc.