Elucidating KChIP effects on Kv4.3 inactivation and recovery kinetics with a minimal KChIP2 isoform.
Kv channel interacting proteins (KChIPs) are Ca(2+)-binding proteins with four EF-hands. KChIPs modulate Kv4 channel gating by slowing inactivation kinetics and accelerating recovery kinetics. Thus, KChIPs are believed to be important regulators of Kv4 channels underlying transient outward K(+) currents in many excitable cell types. We have cloned a structurally minimal KChIP2 isoform (KChIP2d) from ferret heart. KChIP2d corresponds to the final 70 C-terminal amino acids of other KChIPs and has only one EF-hand. We demonstrate that KChIP2d is a functional KChIP that both accelerates recovery and slows inactivation kinetics of Kv4.3, indicating that the minimal C-terminus can maintain KChIP regulatory properties. We utilize KChIP2d to further demonstrate that: (i) the EF-hand modulates effects on Kv4.3 inactivation but not recovery; (ii) Ca(2+)-dependent effects on Kv4.3 inactivation are mediated through a mechanism reflected in the slow time constant of inactivation; and (iii) a short stretch of amino acids exclusive of the EF-hand partially mediates Ca(2+)-independent effects on recovery. Our results demonstrate that distinct regions of a KChIP molecule are involved in modulating inactivation and recovery. The potential ability of KChIP EF-hands to sense intracellular Ca(2+) levels and transduce these changes to alterations in Kv4 channel inactivation kinetics may serve as a mechanism allowing intracellular Ca(2+) transients to modulate repolarization. KChIP2d is a valuable tool for elucidating structural domains of KChIPs involved in Kv4 channel regulation.
Patel
Sangita P
SP
Department of Physiology and Biophysics, University at Buffalo, State University of New York, 124 Sherman Hall, Buffalo, NY 14214, USA. sppatel@acsu.buffalo.edu
Campbell
Donald L
DL
Strauss
Harold C
HC
D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D002118:Calcium / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000502:physiology*; D003001:Cloning, Molecular; D004594:Electrophysiology; D005260:Female; D005289:Ferrets; D006801:Humans; D007700:Kinetics; D051605:Kv Channel-Interacting Proteins; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000502:physiology; D009206:Myocardium / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics; D051580:Neuronal Calcium-Sensor Proteins; D009479:Neuropeptides; D009865:Oocytes; D015221:Potassium Channels / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D020033:Protein Isoforms / Q000502:physiology; D051672:Shal Potassium Channels; D029867:Xenopus Proteins; D014982:Xenopus laevis
D002135:Calcium-Binding Proteins; C497021:KCND3 protein, human; C496752:KCNIP2 protein, human; D051605:Kv Channel-Interacting Proteins; D009419:Nerve Tissue Proteins; D051580:Neuronal Calcium-Sensor Proteins; D009479:Neuropeptides; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D020033:Protein Isoforms; D051672:Shal Potassium Channels; D029867:Xenopus Proteins; C101464:frequenin calcium sensor proteins; D002118:Calcium