Probing conservation of HAMP linker structure and signal transduction mechanism through analysis of hybrid sensor kinases.
The HAMP linker, a predicted structural element observed in many sensor kinases and methyl-accepting chemotaxis proteins, transmits signals between sensory input modules and output modules. HAMP linkers are located immediately inside the cytoplasmic membrane and are predicted to form two short amphipathic alpha-helices (AS-1 and AS-2) joined by an unstructured connector. HAMP linkers are found in the Escherichia coli nitrate- and nitrite-responsive sensor kinases NarX and NarQ (which respond to ligand by increasing kinase activity) and the sensor kinase CpxA (which responds to ligand by decreasing kinase activity). We constructed a series of hybrids with fusion points throughout the HAMP linker, in which the sensory modules of NarX or NarQ are fused to the transmitter modules of NarX, NarQ, or CpxA. A hybrid of the NarX sensor module and the CpxA HAMP linker and transmitter module (NarX-CpxA-1) responded to nitrate by decreasing kinase activity, whereas a hybrid in which the HAMP linker of NarX was replaced by that of CpxA (NarX-CpxA-NarX-1) responded to nitrate by increasing kinase activity. However, sequence variations between HAMP linkers do not allow free exchange of HAMP linkers or their components. Certain deletions in the NarX HAMP linker resulted in characteristic abnormal responses to ligand; similar deletions in the NarQ and NarX-CpxA-1 HAMP linkers resulted in responses to ligand generally similar to those seen in NarX. We conclude that the structure and action of the HAMP linker are conserved and that the HAMP linker transmits a signal to the output domain that ligand is bound.
Appleman
J Alex
JA
Section of Microbiology, University of California, Davis, California 95616-8665, USA. jaappleman@ucdavis.edu
Chen
Li-Ling
LL
Stewart
Valley
V
D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D017124:Conserved Sequence; D003470:Culture Media; D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017384:Sequence Deletion; D015398:Signal Transduction; D013329:Structure-Activity Relationship
D001426:Bacterial Proteins; D003470:Culture Media; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; C088708:narQ protein, E coli; D011494:Protein Kinases; C490475:CpxA protein, E coli; C092472:CpxA protein, bacteria; C074787:narX protein, E coli