NMR STRUCTURE OF INACTIVATION GATES FROM MAMMALIAN VOLTAGE-DEPENDENT POTASSIUM CHANNELS

The electrical signalling properties of neurons originate largely from the gating properties of their ion channels, N-type inactivation of v oltage-gated potassium (K-v) channels is the best-understood gating tr ansition in ion channels, and occurs by a 'ball-and-chain' type mechan ism. In this mechanism an N-terminal domain (inactivation gate), which is tethered to the cytoplasmic side of the channel protein by a prote ase-cleavable chain, binds to its receptor at the inner vestibule of t he channel, thereby physically blocking the pore(1,2). Even when synth esized as a peptide, ball domains restore inactivation in K-v channels whose inactivation domains have been deleted(2,3), Using high-resolut ion nuclear magnetic resonance (NMR) spectroscopy, we analysed the thr ee-dimensional structure of the ball peptides from two rapidly inactiv ating mammalian K-v channels (Raw3 (K(v)3.4) and RCK4 (K(v)1.4)). The inactivation peptide of Raw3 (Raw3-IP) has a compact structure that ex poses two phosphorylation sites and allows the formation of an intramo lecular disulphide bridge between two spatially close cysteine residue s. Raw3-IP exhibits a characteristic surface charge pattern with a pos itively charged, a hydrophobic, and a negatively charged region, The R CK4 inactivation peptide (RCK4-IP) shows a similar spatial distributio n of charged and uncharged regions, but is more flexible and less orde red in its amino-terminal part.