Fig. 1.

Schematic representation of HCN1-R. The six transmembrane segments of a monomeric subunit of the HCN1-R are shown. Six endogenous cysteine residues are removed together with the truncation of the –COOH terminus. Five of the six remaining cysteine residues are replaced by a serine, threonine, or isoleucine substitution. C303 in the S5 segment is left in the final HCN1-R construct because of lack of functional current upon mutations. Their approximate locations, as well as the GYG signature motif, are highlighted as shown. The eight amino acid residues in the P-S6 motif of the final HCN1-R construct are individually replaced by cysteine and named accordingly