A random flight chain model for the tether of the Shaker K+ channel inactivation domain

Rapid inactivation of Shaker K+ channels occurs when a domain in the amino terminal region of the channel protein blocks the pore. Some part of the sequence between the inactivating domain and the first transmembrane segment may form a flexible tether. We consider the possibility that the tether has no secondary structure, but is rather a polypeptide random coil. The local concentration of the tethered inactivation domain and the dependence of the inactivation rate on chain length can then be calculated by using the Jacobson-Stockmayer equation. A chain of 30-100 amino acids is consistent with the sensitivity of the inactivation rate to chain length mutations.