Membrane translocation

Import Receptors and Membrane Translocation of Precursor Peptides 139... 

Recently, there has been significant interest in peptidomimetic forms of Tat49 57, not only because of its membrane translocation activity, but as a means of treating HIV infection [1]. Several peptoids, similar in sequence to Tat49 57, have been synthesized with the intention of preventing the HlV-Tat/Tar interaction, and thus preventing HIV replication [24, 25, 30, 31]. However, only recently has this class of peptoids been applied to membrane translocation and dmg delivery applications. 

Membrane translocating peptides are promising vehicles for the transfer of macromolecules into the tissues. Recent report of Schwarze et al. [249] demonstrated that a signal peptide from Hl-virus could transfer betagalactosidase protein to virtually all tissues in rat after intravenous and intraperitoneal injections. In the case of proteins, folding phenomena affect their membrane translocation and these features may be different for gene-based drugs. 

The amino acid sequences of haptides comprise hydrophobic and cationic residues with a net charge of +4 to +5 per 19 to 21 amino acids. It was proposed that haptides could be attracted to the anionic liposomes as well as the anionic cell membrane and that the hydrophobic properties of the haptide facilitate membrane translocation (106). Haptide uptake was reported to be energy independent, occurring at 4°C. The advantage of this peptide compared to CPP such as TAT and Antp, is that, unlike the virus-derived peptides, the haptides are not recognized as foreign antigens and do not induce cell transformation (106). However, haptides have also been found to accelerate fibrin clot formation and lack cell specificity (106). 

Van Dongen W, Hagen W, van den Berg W, Veeger C. 1988. Evidence for an nnnsual mechanism of membrane translocation of the periplasmic hydrogenase of Desulfovibrio vulgaris (Hildenborough), as derived from expression in Escherichia coli. FEMS Microbiol Lett 50 5-9. 

BoNTs (150 kDa) consist of two polypeptide chains the heavy chain (HC, 100 kDa) and the light chain (LC, 50 kDa), linked with disulfide and non-covalent bonds. The amine end of the LC is responsible for intraneural enzymatic activity. The HC contains a membrane translocation domain (a 50 kDa amino-terminal polypeptide) and a receptor-binding part (a 50 kDa carboxy-terminal polypeptide) (DasGupta, 1990 Krieglstein et ah, 1994). BoNT/A forms dimers, trimers, and bigger structures. BoNT/E generally has a monomer structure, but sometimes forms dimers. BoNT/B is a dimer (Ledoux et ah, 1994). 

Another route to enter cells with Gd(III) chelates is based on the use of membrane translocation peptides which have been proven useful for the internalization of a number of substrates like proteins, oligonucleotides and plasmid DNA. For instance, Bhorade et al. (174) showed that GdDTPA bound to 13-merHIV-tat peptide is efficiently internalized. 

As discussed in Section 11.8.1, many toxins of bacterial or plant origin are built up of different moieties or subunits which mediate binding, membrane translocation and catalytic or... 

Membrane translocation domains have been identified in toxins and viruses and derived from signal sequences of secreted proteins. When derived from a signal seqnence the translocation domain contains hydrophobic sequences [146-148] while the toxin and viral translocation domains contain mostly basic residues [149,150]. 

In terms of targeting, membrane translocation domains lack specificity for particnlar cells or tissues. Therefore, these domains shonld be combined with targeting domains snch as those discussed in the previous section. In snch a constrnct, the targeting domain wiU ensnre a rapid accumulation at the surface of a specific cell type and the translocation domain will facilitate entry into the cytosol of the target cells. 

To function, Ras must be attached to the plasma membrane. Translocation from the cytoplasm to membrane requires a series of posttranslational modifications that begin with farnesylation of the cysteine residue, the fourth amino acid residue from the C terminus of the protein, by famesyl protein transferase (FPTase) (64). Attachment of the hydrophobic 15-carbon lipid farnesyl group allows Ras molecule insertion into the plasma membrane and is crucial for Ras signaling activity and transformation properties. As farnesylation is required for oncogenic Ras function, FPTase inhibitors (FTIs) are obvious candidate antineoplastic agents. Several drugs that inhibit Ras farnesylation are at various stages of clinical development (65). 

A. General description Denileukin dif-titox is a recombinant, DNA-derived, interleukin-2 receptor specific ligand, cytotoxic fusion protein consisting of diphtheria toxin fragments A and B fused to interleukin-2. It is produced by expression of a recombinant fusion protein in Escherichia coli that contains nucleotide sequences for human interleukin-2, and sequences for the enzymatically active fragment A of diphtheria toxin and the membrane-translocating portion of diph-... 

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