Aerotactic Signal Transduction in Halophilic Archaea

University Of Hawaii, Honolulu

Investigators

Abstract

Signal transduction in the Archaeon Halobacterium salinarum provides a paradigm for studying cellular responses to multiple environmental stimuli. Central to these responses is a family of 13 signaling molecules, first discovered in this laboratory. The project will focus on aerophilic transducer HtrVIII and aerophobic transducer HemAT- Hs . The long-term goal of this research is to provide a detailed molecular description of the aerotactic signal transduction system in the halophilic archaeon H. salinarum. Unlike bacterial aerotaxis transducers, HtrVIII has 209 N-terminal residues that form six putative transmembrane helices and are homologous to the oxygen-sensing eukaryotic cytochrome c oxidase subunit I (COXI). The C-terminal domain of HtrVIII is homologous to the signaling and methylation domain of bacterial chemotaxis transducers. It is logical to expect that oxygen binds to a chromophore associated with the six-transmembrane helices and induces conformational changes in the C-terminal domain HtrVIII. This hypothesis will be tested by making mutations within this region. Random mutagenesis in the transmembrane region and site-specific mutagenesis to replace His residues will be used to generate mutants to screen for altered aerotaxis. Heme-containing proteins such as hemoglobin and myoglobin play an essential role in oxygen transport and storage. Recently, this laboratory the first myoglobin-like, heme-containing protein (termed HemAT- Hs ) in the archaeon H. salinarum. HemAT- Hs exhibits two striking features: a) the amino-termini (residues 1 to 184) display limited homology to myoglobin; and b) residues 222 to 489 are 30% identical to the cytoplasmic signaling domain of Tsr, an MCP from E. coli . HemAT- Hs exhibits spectral properties similar to those of myoglobin and triggers aerophobic responses. The goals of this research are to identify: the position of the proximal histidine that is crucial for heme-binding, the functional length of the heme-binding sensing domain, the diatomic oxygen-bound signaling state of the sensing and its activation of the C-terminal signaling domain. This research will provide insight into aerotaxis mechanisms used by the Archaea and open new directions for future research into the strategies used by many motile microorganisms to seek environments with concentrations of oxygen optimal to meet their metabolic needs.