Secondary structure, membrane localization, and coassembly within phospholipid membranes of synthetic segments derived from the N- and C-termini regions of the ROMK1 K+ channel.
The hydropathy plot of the inwardly rectifying ROMK1 K+ channel, which reveals two transmembrane and a pore region domains, also reveals areas of intermediate hydrophobicity in the N terminus (M0) and in the C terminus (post-M2). Peptides that correspond to M0, post-M2, and a control peptide, pre-M0, were synthesized and characterized for their structure, affinity to phospholipid membranes, organizational state in membranes, and ability to self-assemble and coassemble in the membrane-bound state. CD spectroscopy revealed that both M0 and post-M2 adopt highly alpha-helical structures in 1% SDS and 40% TFE/water, whereas pre-M0 is not alpha-helical in either 1% SDS or 40% TFE/water. Binding experiments with NBD-labeled peptides demonstrated that both M0 and post-M2, but not pre-M0, bind to zwitterionic phospholipid membranes with partition coefficients of 10(3)-10(5) M-1. A surface localization for both post-M2 and M0 was indicated by NBD shift, tryptophan quenching experiments with brominated phospholipids, and enzymatic cleavage. Resonance energy transfer measurements between fluorescently labeled pairs of donor (NBD)/ acceptor (rhodamine) peptides revealed that M0 and post-M2 can coassemble in their membrane-bound state, but cannot self-associate when membrane-bound. The results are in agreement with recent data indicating that amino acids in the carboxy terminus of inwardly rectifying K+ channels have a major role in specifying the pore properties of the channels (Taglialatela M, Wible BA, Caporaso R, Brown AM, 1994 Science 264:844-847; Pessia M, Bond CT, Kavanaugh MP, Adelman JP, 1995, Neuron 14:1039-1045). The relevance of the results presented herein to the suggested model for the structure of the ROMK1 channel and to general aspects of molecular recognition between membrane-bound polypeptides are also discussed.
Ben-Efraim
I
I
Department of Membrane Research and Biophysics, Weizmann Institute of Science, Rehovot, Israel.
Shai
Y
Y
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D005456:Fluorescent Dyes; D008563:Membrane Lipids / Q000737:chemistry*; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000737:chemistry*; D015221:Potassium Channels / Q000737:chemistry*; D024661:Potassium Channels, Inwardly Rectifying; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence
D005456:Fluorescent Dyes; D008563:Membrane Lipids; D010743:Phospholipids; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying