SUBSTITUTION OF A HYDROPHOBIC RESIDUE ALTERS THE CONFORMATIONAL STABILITY OF SHAKER K+ CHANNELS DURING GATING AND ASSEMBLY

A leucine residue at position 370 (L370) in 29-4 Shaker K+ channels re sides within two overlapping sequence motifs conserved among most volt age-gated channels: the S4 segment and a leucine heptad repeat. Here w e investigate the effects observed upon substitution of L370 with many other uncharged amino acid residues. We find that smaller or more hyd rophilic residues produce greater alterations in both activation and i nactivation gating than does substitution with other large hydrophobic residues. In addition, subunits containing less conservative substitu tions at position 370 are restricted in their assembly with wild-type subunits and are unlikely to form homomultimeric channel complexes. Co nsistent with the idea that L370 influences the tertiary structure of these channels, the results indicate that L370 undergoes specific hydr ophobic interactions during the conformational transitions of gating; similar interactions may take place during the folding, insertion, or assembly of Shaker K+ channel subunits.