Mutations in the P-region of a mammalian potassium channel (RCK1): a comparison with the Shaker potassium channel.
Deletion mutants of Shaker K channels lacking the middlemost 2 residues of the amino acid sequence GYGD in their P-region lose K-selectivity and become functionally similar to voltage-activated Ca channels. Ca channel characteristics are also conferred on voltage-activated Na channels when residues K in domain III and/or A in domain IV in the P-region of the Na channel are replaced by E residues. In this study, we have investigated a possible evolutionary connection between voltage-activated K and Na channels. Mutant monomeric and multi-heteromeric RCK1 K channel cDNAs were made to match the residues at equivalent positions in the P-region of the Na channel. We found that in contrast to mutant Shaker K channels, the same mutants in RCK1 K channels did not yield functional expression. Therefore possible Na channel-like ion conduction properties conferred on K channels could not be demonstrated. However, our results show that the same mutations in highly homologous channels can produce different effects and point to hitherto unknown structural differences in the P-region of these homologous K channels. Therefore we conclude that extrapolation of the structural and functional importance of residues should be done with caution, even when ion channels belong to the same family.
Tytgat
J
J
Laboratorium voor Fysiologie, O & N, Universiteit Leuven, Belgium.
D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism; D015220:Calcium Channels / Q000737:chemistry; D003001:Cloning, Molecular; D005260:Female; D015870:Gene Expression; D051662:Kv1.1 Potassium Channel; D046911:Macromolecular Substances; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000378:metabolism / Q000502:physiology; D010446:Peptide Fragments; D015221:Potassium Channels / Q000096:biosynthesis / Q000737:chemistry* / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D011487:Protein Conformation; D012333:RNA, Messenger / Q000378:metabolism; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D014982:Xenopus laevis
D015220:Calcium Channels; C489293:Kcna1 protein, rat; D046911:Macromolecular Substances; D010446:Peptide Fragments; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D012333:RNA, Messenger; C088750:S4 peptide, Drosophila Shaker potassium channel; D051662:Kv1.1 Potassium Channel