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Abstract:
Transmembrane receptors are integral components of sensory pathways in prokaryotes. These receptors share a common dimeric architecture, consisting in its basic form of an N-terminal extracellular sensor, transmembrane helices, and an intracellular effector. As an exception, we have identified an archaeal receptor family – exemplified by Af1503 from Archaeoglobus fulgidus – which is C-terminally shortened, lacking a recognizable effector module. Here we examine the gene environment of Af1503-like receptors and identify a closely associated new protein domain family, which we characterize structurally and biochemically using Af1502 from A. fulgidus as a model system. Members of this family are found both as stand-alone proteins and as domains within extant receptors. Invariably, the latter appear as connectors between solute carrier (SLC) protein–like transmembrane domains and two-component signal transduction (TCST) domains. We propose that they mediate signal transduction in systems regulating transport processes, and name the domain STAC, for SLC and TCST Associated Component.
