DNA has numerous attractive features as a scaffold for nanostructure assembly. Its rigidity, predictable structure, and assembly through complementary hybridization allow DNA to form nanoscale architectures such as cubes, [1] tetrahedra, [2] octahedra, [3,4] and 2D arrays. [5][6][7][8] By introducing proteins into DNA nanostructures, the recognition elements and functionalities that are inherent in proteins can be organized into nanostructured motifs. DNA-scaffolded protein assemblies have been used in immuno-PCR detection methods (PCR = polymerase chain reaction) [9][10][11] to arrange biocatalysts in a series for sequential reactions [12,13] and to organize other nanomaterials. [14] There are currently several methodologies used to link proteins to DNA. Proteins have been assembled onto DNA scaffolds through intervening adapter molecules such as streptavidin [12,[15][16][17][18][19][20] or aptamers. [21,22] Alternately, direct covalent conjugation can be achieved by modification of cysteine or lysine residues [23][24][25][26] or intein modification. [11,27,28] Niemyer and co-workers have employed these protein-DNA conjugates to form fluorescence resonant energy transfer (FRET) systems for use in nanobiotechnology. [29,30] Herein, we demonstrate a fusion-based strategy to regioselectively and covalently label proteins at the C terminus with single-stranded DNA. These protein-oligonucleotide chimeras were then spontaneously assembled into nanoarchitectures by complementary hybridization of the DNA. The covalent attachment strategy described herein yields a short and compact linkage between the protein and DNA molecule that allows for precise control over protein spacing and orientation in the final nanostructure.To achieve selective protein labeling, we use the enzyme protein farnesyltransferase (PFTase) to label a substrate protein containing a C-terminal tetrapeptide tag with an azide-modified isoprenoid diphosphate (1, Scheme 1).
DNA has numerous attractive features as a scaffold for nanostructure assembly. Its rigidity, predictable structure, and assembly through complementary hybridization allow DNA to form nanoscale architectures such as cubes, [1] tetrahedra, [2] octahedra, [3,4] and 2D arrays. [5][6][7][8] By introducing proteins into DNA nanostructures, the recognition elements and functionalities that are inherent in proteins can be organized into nanostructured motifs. DNA-scaffolded protein assemblies have been used in immuno-PCR detection methods (PCR = polymerase chain reaction) [9][10][11] to arrange biocatalysts in a series for sequential reactions [12,13] and to organize other nanomaterials. [14] There are currently several methodologies used to link proteins to DNA. Proteins have been assembled onto DNA scaffolds through intervening adapter molecules such as streptavidin [12,[15][16][17][18][19][20] or aptamers. [21,22] Alternately, direct covalent conjugation can be achieved by modification of cysteine or lysine residues [23][24][25][26] or intein modification. [11,27,28] Niemyer and co-workers have employed these protein-DNA conjugates to form fluorescence resonant energy transfer (FRET) systems for use in nanobiotechnology. [29,30] Herein, we demonstrate a fusion-based strategy to regioselectively and covalently label proteins at the C terminus with single-stranded DNA. These protein-oligonucleotide chimeras were then spontaneously assembled into nanoarchitectures by complementary hybridization of the DNA. The covalent attachment strategy described herein yields a short and compact linkage between the protein and DNA molecule that allows for precise control over protein spacing and orientation in the final nanostructure.To achieve selective protein labeling, we use the enzyme protein farnesyltransferase (PFTase) to label a substrate protein containing a C-terminal tetrapeptide tag with an azide-modified isoprenoid diphosphate (1, Scheme 1).
Protein prenylation is a common post-translational modification present in eukaryotic cells. Many key proteins involved in signal transduction pathways are prenylated and inhibition of prenylation can be useful as a therapeutic intervention. While significant progress has been made in understanding protein prenylation in vitro, we have been interested in studying this process in living cells, including the question of where prenylated molecules localize. Here, we describe the synthesis and live cell analysis of a series of fluorescently labeled multifunctional peptides, based on the C-terminus of the naturally prenylated protein CDC42. A synthetic route was developed that features a key Acm to Scm protecting group conversion. This strategy was compatible with acid-sensitive isoprenoid moieties, and allowed incorporation of an appropriate fluorophore as well as a cell-penetrating sequence (penetratin). These peptides are able to enter cells through different mechanisms, depending on the presence or absence of the penetratin vehicle and the nature of the prenyl group attached. Interestingly, prenylated peptides lacking penetratin are able to enter cells freely through an energy-independent process, and localize in a perinuclear fashion. This effect extends to a prenylated peptide that includes a full “CAAX box” sequence (specifically, CVLL). Hence, these peptides open the door for studies of protein prenylation in living cells, including enzymatic processing and intracellular peptide trafficking. Moreover, the synthetic strategy developed here should be useful for the assembly of other types of peptides that contain acid sensitive functionalities.
Recently a number of non-natural prenyl groups containing alkynes and azides have been developed as handles to perform click chemistry on proteins and peptides ending in the sequence "CAAX", where C is a cysteine that becomes alkylated, A is an aliphatic amino acid and X is any amino acid. When such molecules are modified, a tag containing a prenyl analog and the "CAAX box" sequence remains. Here we report the synthesis of an alkyne-containing substrate comprised of only nine non-hydrogen atoms. This substrate was synthesized in six steps from 3-methyl-2-buten-1-ol and has been enzymatically incorporated into both proteins and peptides using protein farnesyltransferase. After prenylation the final three amino acids required for enzymatic recognition can be removed using carboxypeptidase Y, leaving a single residue (the cysteine from the "CAAX box") and the prenyl analog as the only modifications. We also demonstrate that this small tag minimizes the impact of the modification on the solubility of the targeted protein. Hence, this new approach should be useful for applications in which the presence of a large tag hinders the modified protein's solubility, reactivity or utility.
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