Secondary conformational conversion is involved in glycosaminoglycans-mediated cellular uptake of the cationic cell-penetrating peptide PACAP.

Glycosaminoglycans (GAGs) contribute to the cellular uptake of cationic cell-penetrating peptides (CPPs). However, molecular details about the contributions of GAGs in CPP internalization remain unclear. In this study, we examined the cellular uptake mechanism of the arginine-rich CPP pituitary adenylate-cyclase-activating polypeptide (PACAP). We observed that the uptake efficacy of PACAP is dependent on the expression of cell surface GAGs. As the binding of PACAP to sulfated GAGs induced a random coil-to-α-helix conformational conversion, we investigated the role of the helical formation in PACAP internalization. Whereas this secondary structure was not crucial for efficient internalization in GAGs-deficient cells, PACAP α-helix was essential for GAGs-dependent uptake.