Proteolytic activation of a hyperpolarization- and calcium-dependent potassium channel in Paramecium.
The effects of proteolysis on a hyperpolarization- and Ca2+-dependent K channel from the surface membrane of Paramecium tetraurelia were examined in the inside-out excised patch mode. Treatment with trypsin, pronase or thermolysin removed the Ca2+-dependence of the channel activation, yielding an increase in channel activity greater than 2.5-fold at all Ca2+ concentrations between 10(-4) and 10(-8) M. Thermolysin additionally removed the voltage dependence of channel opening and gave the most activation among the three proteases tested. Proteolysis did not affect the single-channel conductance. In an analogy to the mechanism of activation of many Ca2+-dependent enzymes it is suggested that this Paramecium channel has a cytoplasmic inhibitory domain which can be removed by proteolysis, and that the physiological activation by Ca2+ is due to a temporary removal of this inhibition. Moreover, these findings indicate structural differences between depolarization-, Ca2+-dependent K channels (BK channels) and the hyperpolarization-, Ca2+-dependent K channels in Paramecium.
Kubalski
A
A
Laboratory of Molecular Biology, University of Wisconsin, Madison 53706.
Martinac
B
B
Saimi
Y
Y
D000818:Animals; D002118:Calcium / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D010247:Paramecium / Q000187:drug effects / Q000502:physiology*; D010447:Peptide Hydrolases / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D011402:Pronase / Q000378:metabolism; D013820:Thermolysin / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
D015221:Potassium Channels; D010447:Peptide Hydrolases; D014357:Trypsin; D011402:Pronase; D013820:Thermolysin; D002118:Calcium