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

Enzymatic catalysis and protein signaling are dynamic processes that involve local and/or global conformational changes occurring across a broad range of time scales. 1H-15N 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 sulfate transporter and anti-sigma factor antagonist (STAS) domain of Rv1739c, a SulP anion transporter protein of Mycobacteriumtuberculosis . In the present study, we report 1H-15N NMR backbone dynamics measurements [longitudinal (T 1), transverse (T 2) and steady-state ({1H}-15N) 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 the binding of GTP and GDP to Rv1739c STAS. The 9.55ns overall rotational correlation time of Rv1739c STAS increased to 10.48ns in the presence of GTP, and to 13.25ns in the presence of GDP, indicating significant nucleotide-induced conformational changes. These conformational changes were accompanied by slow time scale (μs to ms) motions in discrete regions of the protein, as reflected by guanine nucleotide-induced changes in relaxation parameters. The observed nucleotide-specific alterations in the relaxation properties of individual STAS residues reflect an increased molecular anisotropy and/or the emergence of conformational equilibria governing functional properties of the STAS domain. The effects of guanine nucleotides on the backbone dynamics of M.tuberculosis Rv1739c STAS domain were studied by analyzing 1H-15N relaxation NMR data using model-free formalism and reduced spectral density function approach. GTP and GDP induced distinct conformational changes in discrete regions of the STAS domain. GDP-STAS in general exhibited larger changes in dynamic parameters than GTP-STAS. [PUBLICATION ABSTRACT]