The heptapeptide sequence Gly-Gly-Gly-Pro-Gly-Gly-Gly, when anchored to diglycolic acid derived (C₁₈H₃₇)₂NCOCH₂OCH₂COOH, forms chloride-selective ion channels in phospholipid liposomes but the related heptapeptide Gly-Gly-Gly-Leu-Gly-Gly-Gly, and tripeptide Gly-Gly-Gly do not.