Journal
BIOCHEMISTRY
Volume 43, Issue 9, Pages 2438-2444Publisher
AMER CHEMICAL SOC
DOI: 10.1021/bi035933x
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Funding
- NCI NIH HHS [CA73808] Funding Source: Medline
- NIGMS NIH HHS [R01 GM044783, R01 GM044783-12, GM44783] Funding Source: Medline
- PHS HHS [08349] Funding Source: Medline
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Cationic peptides known as protein transduction domains (PTDs) provide a means to deliver molecules into mammalian cells. Here, nonaarginine (R-9), the most efficacious of known PTDs, is used to elucidate the pathway for PTD internalization. Although R-9 is found in the cytosol as well as the nucleolus when cells are fixed, this peptide is observed only in the endocytic vesicles of live cells. Colocalization studies with vesicular markers confirm that PTDs are internalized by endocytosis rather than by crossing the plasma membrane. The inability of R-9 to enter living cells deficient in heparan sulfate (HS) suggests that binding to HS is necessary for PTD internalization. This finding is consistent with the high affinity of R-9 for heparin (K-d = 109 nM). Finally, R-9 is shown to promote the leakage of liposomes but only at high peptide:lipid ratios. These and other data indicate that the PTD-mediated delivery of molecules into live mammalian cells involves (1) binding to cell surface HS, (2) uptake by endocytosis, (3) release upon HS degradation, and (4) leakage from endocytic vesicles.
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