The Mycobacterium tuberculosis transcriptional regulator Rv1364c regulates the
activity of the stress response sigma factor sigma(F). This multi-domain protein
has several components: a signaling PAS domain and an effector segment
comprising of a phosphatase, a kinase and an anti-anti- sigma factor domain.
Based on Small Angle X-Ray Scattering (SAXS) data, Rv1364c was recently shown to
be a homo-dimer and adopt an elongated conformation in solution. The PAS domain
could not be modeled into the structural envelope due to poor sequence
similarity with known PAS proteins. The crystal structure of the PAS domain
described here provides a structural basis for the dimerization of Rv1364c. It
thus appears likely that the PAS domain regulates the anti- sigma activity of
Rv1364c by oligomerization. A structural comparison with other characterized PAS
domains reveal several sequence and conformational features that could
facilitate ligand binding- a feature which suggests that the function of Rv1364c
could potentially be governed by specific cellular signals or metabolic cues.
