Solution Structure of the Guanine Nucleotide-binding STAS Domain of SLC26-related SulP Protein Rv1739c from Mycobacterium tuberculosis

Abstract

The structure and intrinsic activities of conserved STAS domains of the ubiquitous SulP/SLC26 anion transporter superfamily have until recently remained unknown. Here we report the heteronuclear, multidimensional NMR spectroscopy solution structure of the STAS domain from the SulP/SLC26 putative anion transporter Rv1739c of Mycobacterium tuberculosis. The 0.87-Å root mean square deviation structure revealed a four-stranded ␤-sheet with five interspersed ␣-helices, resembling the anti-factor antagonist fold. Rv1739c STAS was shown to be a guanine nucleotide-binding protein, as revealed by nucleotide-dependent quench of intrinsic STAS fluorescence and photoaffinity labeling. NMR chemical shift perturbation analysis partnered with in silico docking calculations identified solvent-exposed STAS residues involved in nucleotide binding. Rv1739c STAS was not an in vitro substrate of mycobacterial kinases or anti-factors. These results demonstrate that Rv1739c STAS binds guanine nucleotides at physiological concentrations and undergoes a ligand-induced conformational change but, unlike anti-factor antagonists, may not mediate signals via phosphorylation.

SLC26 anion exchangers of guinea pig pancreatic duct: molecular cloning and functional characterization

“…However, the fundamental domain architectures of each guinea pig protein are conserved with their species orthologs. The most remarkable exception is the Slc26a11-specific absence of a STAS domain INV loop, a property shared with STAS domains of bacterial SulP proteins (4,43) and with bacterial anti-sigma factor antagonists (3). The Slc26a11 transmembrane domain has been modeled with 11 transmembrane domains and an extracellular NH 2 -terminus (57), in contrast to the consensus SulP/SLC26 structure of 12 …”

N-glycosylation and topology of the human SLC26 family of anion transport membrane proteins

“…The proteins all consist of two major domains: a NH 2 -terminal membrane domain with ϳ12 putative transmembrane (TM) segments and a COOH-terminal STAS (sulfate transporter antagonist of anti-sigma factor) domain located in the cytosol (53). Structures of the STAS domain of several bacterial members of the SLC26 family have been obtained (4,54), as well as the structure of a modified version of the STAS domain of rat SLC26A5 protein (40). All of the core structures resemble the Bacillus anti-sigma factor antagonist SpoIIAA, a 110 amino acid phospho-protein with an alpha/beta topology consisting of a central four-stranded beta sheet sandwiched between three peripheral alpha helices (2,52).…”

Molecular Dynamics Simulations of the STAS Domains of Rat Prestin and Human Pendrin Reveal Conformational Motions in Conserved Flexible Regions

“…The differential distribution of crosspeak intensities noted in the 1 H- 15 N 2D HSQC spectrum was also consistent with intrinsic dynamic features of protein conformation. Comparison of STAS domain structures reveals that packing of helix α 1 with respect to helix α 2 is strikingly different in rat prestin [11] than in the two bacterial SulP STAS structures [7,9]. The α 1 -α 2 inter-helical angle described by the two helical axes in rat prestin STAS is substantially greater than in the STAS domains of Rv1739c and ychM.…”

“…We hypothesized that such simulation studies might address the possible contributions to determination of the STAS domain α 1 -α 2 inter-helical angles by the 11 additional aa residues not visualized in the rat prestin structures [11]. We also hypothesized a possible relationship between the most mobile residues of rat prestin STAS domain with the guanine nucleotide-interacting residues of M. tuberculosis Rv1739c STAS domain [10] which tended to exhibit increased mobility [9]. …”

“…The STAS domains of bacterial SulP anion transport proteins subjected to structural analysis include STAS domains of E. coli ychM (in spontaneous complex with malonyl-coA-liganded acyl carrier protein) [7] and of M. tuberculosis Rv1739c [8,9] shown to bind guanine nucleotides [10]. Prokaryotic STAS domains differ from eukaryotic STAS domains in lacking the nominally unstructured “ i ntervening v ariable s equence” (IVS) present in the latter.…”