InterPro domain: IPR002645

The STAS (Sulphate Transporter and AntiSigma factor antagonist) domain is found in the bacterial anti-sigma factor antagonists (ASA) and the C-terminal region of SLC26 (SulP) anion transporters.

The activity of bacterial sigma transcription factors is controlled by a regulatory cascade involving an antisigma-factor, the antisigma-factor antagonist (ASA) and a phosphatase. The antisigma-factor binds to sigma and holds it in an inactive complex. The ASA can also interact with the anti-sigma-factor, allowing the release of the active sigma factor. As the antisigma-factor is a protein kinase, it can phosphorylate the antisigma antagonist on a conserved serine residue of the STAS domain. This phosphorylation inactivates the ASA that can be reactivated through dephosphorylation by a phosphatase [ 1 , 2 ]. The STAS domain of the ASA SpoIIAA binds GTP and ATP and possesses a weak NTPase activity. Strong sequence conservation suggests that the STAS domain could possess general NTP-binding activity, and it has been proposed that the NTPs are likely to elicit specific conformational changes in the STAS domain through binding and/or hydrolysis [ 3 ]. Resolution of the solution structure of the ASA SpoIIAA from Bacillus subtilis has shown that the STAS domain consists of a four-stranded beta-sheet and four alpha helices. The STAS domain forms a characteristic alpha-helical handle-like structure [ 3 , 3 ].

The STAS domain of E. coli YchM protein, a SLC26 (SulP) family member, has been shown to interact with acyl carrier protein (ACP), which is an activated thiol ester carrier of acyl intermediates during fatty acid biosynthesis (FAB) and other acylation reactions [ 4 ].

Malfunctions in members of the SLC26A family of anion transporters are involved in three human diseases: diastrophic dysplasia/achondrogenesis type 1B (DTDST), Pendred's syndrome (PDS) and congenital chloride diarrhea (CLD). These proteins contain 12 transmembrane helices followed by a cytoplasmic STAS domain at the C terminus. The importance of the STAS domain in these transporters is illustrated by the fact that a number of mutations in PDS and DTDST map to it [ 5 , 5 ].

1. The STAS domain - a link between anion transporters and antisigma-factor antagonists. Curr. Biol. 10, R53-5
2. Characterization of a morphological checkpoint coupling cell-specific transcription to septation in Bacillus subtilis. Mol. Microbiol. 33, 1015-26
3. Solution structure of SpoIIAA, a phosphorylatable component of the system that regulates transcription factor sigmaF of Bacillus subtilis. Proc. Natl. Acad. Sci. U.S.A. 95, 5067-71
4. Structure of a SLC26 anion transporter STAS domain in complex with acyl carrier protein: implications for E. coli YchM in fatty acid metabolism. Structure 18, 1450-62
5. STAS domain structure and function. Cell. Physiol. Biochem. 28, 407-22