Crystal Structure of the Sugar Binding Domain of the Archaeal Transcritional Regulator TrmB

Abstract

TrmB is an alpha-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 was solved at 1.5A resolution. This protein has lost its DNA binding domain but has retained its sugar recognition site. The structure represents a novel sugar-binding fold. TrmB bound maltose, glucose, sucrose, and maltotriose, exhibiting Kd values of 6.8, 25, 34, and 160 μM, respectively. TrmB 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.