The S Helix Mediates Signal Transmission as a HAMP Domain Coiled-Coil Extension in the NarX Nitrate Sensor from Escherichia coli K-12

摘要: In the nitrate-responsive, homodimeric NarX sensor, two cytoplasmic membrane alpha-helices delimit periplasmic ligand-binding domain. The HAMP domain, a four-helix parallel coiled-coil built from (HD1 and HD2), immediately follows second transmembrane helix. Previous computational studies identified likely coiled-coil-forming alpha-helix, signaling helix (S helix), in range of proteins, including eucaryal receptor guanylyl cyclases, but its function remains obscure. NarX, HD2 S-helix regions overlap apparently form continuous marked by heptad repeat stutter discontinuity at distal boundary HD2. Similar composite HD2-S-helix elements are present other sensors, such as Sln1p Saccharomyces cerevisiae. We constructed deletions missense substitutions S Most caused constitutive phenotypes. However, strongly impaired induction phenotypes were conferred within conserved core also that remove stutter. latter observation illuminates key element dynamic bundle hypothesis for across adjacent to domain methyl-accepting chemotaxis proteins (Q. Zhou, P. Ames, J. S. Parkinson, Mol. Microbiol. 73:801-814, 2009). Sequence comparisons examples stutters between contiguous coiled-coil-like sequence conventional CpxA, EnvZ, PhoQ, QseC; S-helix-containing BarA TorS; Neurospora crassa Nik-1 (Os-1) sensor contains tandem array alternating HAMP-like elements. Therefore, may be broadly important function.