Tryptophan within basic peptide sequences triggers glycosaminoglycan-dependent endocytosis

Area of Science:

• Biochemistry
• Molecular Biology
• Drug Delivery

Background:

• Cell-penetrating peptides (CPPs) are crucial for delivering molecules into cells.
• Understanding CPP structural requirements for internalization is key to improving delivery efficiency.

Purpose of the Study:

• To characterize the role of tryptophan (Trp) residues in CPP interaction with glycosaminoglycans (GAGs).
• To correlate Trp-mediated CPP-GAG interactions with cellular internalization mechanisms.

Main Methods:

• Isothermal titration calorimetry
• Circular dichroism
• NMR spectroscopy
• Mass spectrometry
• Phase-contrast microscopy

Main Results:

• CPP affinity for GAGs, like heparin, increased linearly with the number of Trp residues.
• Trp-containing CPPs adopted a β-strand structure and formed stable β-sheet aggregates with GAGs.
• Cellular internalization of CPPs increased significantly with Trp content, without cytotoxicity.

Conclusions:

• Tryptophan residues are critical determinants for CPP interaction with GAGs.
• Trp residues facilitate both direct membrane translocation and GAG-mediated endocytosis.
• This finding provides a basis for designing more effective CPP-based delivery systems.