Guanine nucleotides differentially modulate backbone dynamics of the STAS domain of the SulP/SLC26 transport protein Rv1739c of M. tuberculosis

Enzymatic catalysis and protein signaling are dynamic processes that involve local and/or global conformational changes that occur across a broad range of time scales. 1 H- 15 N relaxation NMR provides a comprehensive understanding of protein backbone dynamics both in the apo (unliganded) and ligand-bound conformations enabling both fast and slow internal motions of individual amino acid residues to be observed. We recently reported the structure and nucleotide binding properties of the STAS domain of Rv1739c, a SulP anion transporter protein of M. tuberculosis . In this report we present 1 H- 15 N NMR backbone dynamics measurements ( T 1 , T 2 and steady-state ({ 1 H}- 15 N) heteronuclear NOE) of the Rv1739c STAS domain, in the absence and presence of saturating concentrations of GTP and GDP. Analysis of measured relaxation data and estimated dynamic parameters indicated distinct features differentiating binding of GTP and GDP to Rv1739c STAS. The 9.55 nsec overall rotational correlation time (τ m ) of Rv1739c STAS increased to 10.48 nsec in the presence of GTP, and to 13.25 nsec in the presence of GDP, indicating significant nucleotide-induced conformational changes. These conformational changes were accompanied by slow time scale (μsec-msec) motions in discrete regions of the protein, reflected in guanine nucleotide-induced changes in relaxation parameters. The observed nucleotide-specific alterations in relaxation properties of individual STAS residues reflect increased molecular anisotropy and/or the emergence of conformational equilibria governing functional properties of the STAS domain.