The H(2) sensor of Ralstonia eutropha is a member of the subclass of regulatory [NiFe] hydrogenases.
Two energy-generating hydrogenases enable the aerobic hydrogen bacterium Ralstonia eutropha (formerly Alcaligenes eutrophus) to use molecular hydrogen as the sole energy source. The complex synthesis of the nickel-iron-containing enzymes has to be efficiently regulated in response to H(2), which is available in low amounts in aerobic environments. H(2) sensing in R. eutropha is achieved by a hydrogenase-like protein which controls the hydrogenase gene expression in concert with a two-component regulatory system. In this study we show that the H(2) sensor of R. eutropha is a cytoplasmic protein. Although capable of H(2) oxidation with redox dyes as electron acceptors, the protein did not support lithoautotrophic growth in the absence of the energy-generating hydrogenases. A specifically designed overexpression system for R. eutropha provided the basis for identifying the H(2) sensor as a nickel-containing regulatory protein. The data support previous results which showed that the sensor has an active site similar to that of prototypic [NiFe] hydrogenases (A. J. Pierik, M. Schmelz, O. Lenz, B. Friedrich, and S. P. J. Albracht, FEBS Lett. 438:231-235, 1998). It is demonstrated that in addition to the enzymatic activity the regulatory function of the H(2) sensor is nickel dependent. The results suggest that H(2) sensing requires an active [NiFe] hydrogenase, leaving the question open whether only H(2) binding or subsequent H(2) oxidation and electron transfer processes are necessary for signaling. The regulatory role of the H(2)-sensing hydrogenase of R. eutropha, which has also been investigated in other hydrogen-oxidizing bacteria, is intimately correlated with a set of typical structural features. Thus, the family of H(2) sensors represents a novel subclass of [NiFe] hydrogenases denoted as the "regulatory hydrogenases."
Kleihues
L
L
Institut für Biologie, Humboldt-Universität zu Berlin, 10115 Berlin, Germany.
Lenz
O
O
Bernhard
M
M
Buhrke
T
T
Friedrich
B
B
D000595:Amino Acid Sequence; D020118:Cupriavidus necator / Q000201:enzymology* / Q000235:genetics; D003593:Cytoplasm / Q000378:metabolism; D003903:Deuterium / Q000378:metabolism; D006864:Hydrogenase / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D008969:Molecular Sequence Data; D009532:Nickel / Q000378:metabolism; D010084:Oxidation-Reduction; D017386:Sequence Homology, Amino Acid; D012995:Solubility
D009532:Nickel; D003903:Deuterium; C043296:nickel-iron hydrogenase; D006864:Hydrogenase