Search

Conventional protein engineering methods for modifying protein nanopores are typically limited to 20 natural amino acids, which restrict the diversity of the nanopores in structure and function. To enrich the chemical environment inside the nanopore, we employed the genetic code expansion (GCE) technique to site‐specifically incorporate the unnatural amino acid (UAA) into the sensing region of aerolysin nanopores. This approach leveraged the efficient pyrrolysine‐based aminoacyl‐tRNA synthetase‐tRNA pair for a high yield of pore‐forming protein. Both molecular dynamics (MD) simulations and single‐molecule sensing experiments demonstrated that the conformation of UAA residues provided a favorable geometric orientation for the interactions of target molecules and the pore. This rationally designed chemical environment enabled the direct discrimination of multiple peptides containing hydrophobic amino acids. Our work provides a new framework for endowing nanopores with unique sensing properties that are difficult to achieve using classical protein engineering approaches. [ABSTRACT FROM AUTHOR]

Tau phosphorylation shows direct clinical importance as the hyperphosphorylation and aggregation of tau exists in a range of tauopathies. However, it is still challenging to study tau phosphorylation owing to its multiple and adjacent phosphorylation sites in the tau sequence. To address this challenge, here, a designed T232K/K238Q mutant aerolysin nanopore is introduced which synergistically incorporates the enhanced electrostatic interaction at T232K site and the high repelling barrier at K238Q site. The distinct current blockages produced by a T232K/K238Q aerolysin sensor achieve nearly 100% identification accuracy for the characteristic distribution of unphosphorylated tau peptide, pS262‐, pT263‐tau peptide, and pS262/pT263‐tau peptide. The excellent sensing ability of the T232K/K238Q nanopore originates from the extremely slow translocation speed which prolongs the duration up to tens or hundreds milliseconds for a nine‐amino‐acid peptide. It is envisioned that the design ideas of the T232K/K238Q aerolysin nanopore can be further applied to analyze other protein/peptide post‐translational modification as it provides the exquisite sensitivity for identifying the modification of single amino acids. [ABSTRACT FROM AUTHOR]

A fluorophilic fluorescent probe based on a perfluoroalkyl‐substituted bis(binaphthyl) compound was designed and synthesized. It displayed a highly enantioselective fluorescence response toward structurally diverse amino acids in a biphasic fluorous/aqueous system with enantiomeric fluorescent enhancement ratio (ef; ΔID/ΔIL) values up to 45.2 (histidine). It can be used to determine the enantiomeric compositions of amino acids and also allows the amino acid enantiomers to be visually discriminated. NMR and mass‐spectroscopic investigations provided insights into the observed high enantioselectivity. This biphasic fluorescent recognition was used to determine the enantiomeric composition of the crude phenylalanine products generated by an enzyme‐catalyzed asymmetric hydrolysis under various reaction conditions. The fluorous‐phase‐based fluorescence measurement under the biphasic conditions was able to minimize the interference of other reaction components and thus has potential in asymmetric reaction screening. [ABSTRACT FROM AUTHOR]

A new strategy for fast fluorescent detection of cysteine (Cys), based on a response-assisted electrostatic attraction, is demonstrated. By utilizing this strategy, we designed and synthesized three fluorescent probes for the specific detection of Cys under actual physiological conditions. The probe m- CP, a coumarin fluorophore conjugated with a substituted methyl pyridinium group through an unsaturated ketone unit, showed highly selective and sensitive detection for cysteine (Cys) over homocysteine (Hcy) and glutathione (GSH). The kinetic analysis indicated that the sensing process was highly accelerated (a response time less than 1 min) by the response-assisted electrostatic attraction. More importantly, control experiments with isomeric probes first demonstrated that the spatial charge configuration of the probe played an important role in Cys-preferred selectivity and kinetic rate acceleration. Furthermore, the practical utility of the probe m- CP in the fluorescent labeling of Cys residues within proteins was demonstrated. Finally, these probes were employed in living cell imaging with HeLa cells, in which it displayed satisfactory cell permeability and enabled us to distinguish active thiols in the cytoplasm, nucleus, and mitochondria. [ABSTRACT FROM AUTHOR]