A structural motif in the C-terminal tail of slo1 confers carbon monoxide sensitivity to human BK Ca channels.
Carbon monoxide (CO) is a potent activator of large conductance, calcium-dependent potassium (BK Ca) channels of vascular myocytes and carotid body glomus cells or when heterologously expressed. Using the human BK Ca channel alpha1-subunit (hSlo1; KCNMA1) stably and transiently expressed in human embryonic kidney 293 cells, the mechanism and structural basis of channel activation by CO was investigated in inside-out, excised membrane patches. Activation by CO was concentration dependent (EC50 approximately 20 microM), rapid, reversible, and evoked a shift in the V 0.5 of -20 mV. CO evoked no changes in either single channel conductance or in deactivation rate but augmented channel activation rate. Activation was independent of the redox state of the channel, or associated compounds/protein partners, and was partially dependent on [Ca2+]i in the physiological range (100-1,000 nM). Importantly, CO "super-stimulated" BK Ca activity even in saturating [Ca2+]i. Single or double mutation of two histidine residues previously implicated in CO sensing did not suppress CO activation but replacing the S9-S10 module of the C-terminal of Slo1 with that of Slo3 completely prevented the action of CO. These findings show that a motif in the S9-S10 part of the C-terminal is essential for CO activation and suggest that this gas transmitter activates the BK Ca channel by redox-independent changes in gating.
Williams
Sandile E
SE
School of Biosciences, Cardiff University, Cardiff, UK.
Brazier
Stephen P
SP
Baban
Nian
N
Telezhkin
Vsevolod
V
Müller
Carsten T
CT
Riccardi
Daniela
D
Kemp
Paul J
PJ
D020816:Amino Acid Motifs; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002248:Carbon Monoxide / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D015640:Ion Channel Gating; D007700:Kinetics; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D018408:Patch-Clamp Techniques; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D014162:Transfection
C494841:KCNMA1 protein, human; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D002248:Carbon Monoxide; D002118:Calcium