The role and synthesis of cell-penetrating peptides

Penetrating the cell membrane and entering the cell is a prerequisite for many biological macromolecules that target cells to function. However, the biological barrier function of the biomembrane prevents many macromolecular substances from entering the cell, thus greatly limiting the application of these substances in the therapeutic field. Therefore, how to guide these substances to penetrate the cell membrane is an urgent problem that needs to be solved. The current methods to mediate the penetration of biological macromolecules into the cell membrane mainly include cell-penetrating peptides (cell penetrating peptides, CPPs), Liposomes, adenovirus, nanoparticles, ghost cells, etc., while CPPs It is a type of polypeptide that directly crosses the cell membrane and enters the cell in a non-receptor-dependent and non-classical endocytosis manner. Their length is generally no more than 30 amino acids and they are rich in basic amino acids. The amino acid sequence is usually positively charged.

1human immunodeficiency virus transcriptional activator TAT(human immunodeficiency virus-1 transcription activator, HIV-1 TAT) It is the first cell-penetrating peptide discovered, which enters cells in a non-toxic and efficient way.

cell penetrating peptide (cell penetrating peptides, CPPs) An important feature of it is that it can carry a variety of biologically active substances of different sizes and properties into cells, including small molecule compounds, dyes, peptides, and peptide nucleic acids (peptide nucleo acid, PNA), protein, plasmid DNA, siRNA, 200nm Liposomes, phage particles and superparamagnetic particles, etc. This property provides the possibility for them to become good carriers for targeted drugs.

CPPs Advantages as a vector are low toxicity and no cell type limitations, although CPPs It can transport different types of substances into cells, but its practical applications are mostly focused on oligopeptides, proteins, and oligonucleotides (oligonucleotides, ONs)or similar cellular transport.
 

Different cell-penetrating peptides (CPP) Different transmembrane mechanisms, a cell-penetrating peptide (CPP) The specific mechanism depends on several parameters, such as molecular size (carrying substances), temperature, cell type and stability inside and outside the cell. cell penetrating peptide (CPP) The specific mechanism of entry into cells is currently unclear. Popular speculations include the following three:
A: Inverted colloidal particle model (inverted micelle model), CPPs Through the movement of phospholipid molecules on the cell membrane, an inverted colloidal structure is formed and enters the cytoplasm.
B: Direct penetration, i.e. pore structure model (pore formation model), CPPs Form a transmembrane pore structure on the cell membrane and enter the cytoplasm.
C: Cellular uptake by endocytosis.
source: Cell-penetrating peptides and their therapeutic applications, Victoria Sebbage, BioscienceHorizons, Volume 2, Number 1, March 2009.

Cell-penetrating peptides (e.g. HIV TAT) It can enter cells in two ways: direct penetration and endocytosis. HIV TAT Or simple polyarginine could be designed as an effective drug carrier, but CPP(like HIV TAT) How membrane transport is achieved is still unclear.
simple HIV TAT How are cell entry mechanisms such as direct penetration and endocytosis promoted? from Gerard Wong Researchers in the laboratory studied under different conditions HIV TAT How it interacts with the cytoplasmic membrane, cytoskeleton, and specific membrane receptors, thereby inducing multiple transport pathways.

Interestingly, TAT A variety of different reactions can occur with the same sequence under different conditions, thus interacting with the cell membrane, cytoskeleton, and specific receptors can produce multiple transport pathways.

CPP There is a very sensitive relationship between the transmembrane mechanism and the polypeptide sequence. If in a purely hydrophilic CPP Adding a hydrophobic residue to it can completely change its transport mechanism. For example, the simplest CPP Prototype-polyarginine (polyR), Can induce the formation of transmembrane pore structures on the cell membrane. Hydrophobic amino acids form positive curvature by inserting into the cell membrane. Arginine can form both positive and negative curvature at the same time. Lysine can only form negative curvature in one direction. This means that between arginine and lysine /There is a compensatory relationship between hydrophobes.

If hydrophobicity contributes to negative Gaussian curvature (Gaussian curvature), then why TAT What about the relatively low hydrophobic content of the peptide? The reason is CPPs They all use as few hydrophobic groups as possible to form saddle-splay curvature. Differences in sequence most likely induce only transient pore-like transmembrane structures in the membrane, creating a pair CPP for shorter pore life. because CPP The amino acid composition of TAT Peptides can mediate endocytosis with or without receptors.