We recently reported a computational method (CHAMP) for designing sequence-specific peptides that bind to the membrane-embedded portions of transmembrane proteins. We successfully applied this method to design membrane-spanning peptides targeting the transmembrane domains of the αIIb subunit of integrin αIIbβ 3. Previously, we demonstrated that these CHAMP peptides bind specifically with reasonable affinity to isolated transmembrane helices of the targeted transmembrane region. These peptides also induced integrin αIIbβ3 activation due to disruption of the helix-helix interactions between the transmembrane domains of the αIIb and β3 subunits. In this paper, we show the direct interaction of the designed anti-αIIb CHAMP peptide with isolated full-length integrin αIIbβ3 in detergent micelles. Further, the behavior of the designed peptides in phospholipid bilayers is essentially identical to their behavior in detergent micelles. In particular, the peptides assume a membrane-spanning α-helical conformation that does not disrupt bilayer integrity. The activity and selectivity of the CHAMP peptides were further explored in platelets, comfirming that anti-αIIb activates wild-type αIIbβ 3 in whole cells as a result of its disruption of the protein-protein interactions between the α and β subunits in the transmembrane regions. These results demonstrate that CHAMP is a successful chemical biology approach that can provide specific tools for probing the transmembrane domains of proteins.
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