Stimuli-responsive Polypeptide Research Articles

Toward Designing Smart Nanovalves: Modeling of Flow Control through Nanopores via the Helix−Coil Transition of Grafted Polypeptide Chains

Nanopores modified with stimuli-responsive polypeptide chains offer a smart flow-control mechanism. These unique materials have potential wide-ranging applications including smart drug delivery, bioimplants, and molecular machines. Here, we develop a continuum method to analyze flow control through nanopores grafted with polypeptide chains. The helix−coil transition of the polypeptide chains triggered by pH change enables flow regulation. The conformational transition is treated within the Zimm−Bragg model to determine the monomer density profile of the grafted layer inside a nanopore as a function of pH. The Brinkman equation for flow through porous materials is then used to calculate the flow rate. The results are compared with recent experiments in which pH-responsive water permeation through a poly(l-glutamic acid) grafted nanoporous membrane is achieved. The results establish that polymer statistical mechanics combined with a continuum porous layer treatment of flow through the polypeptide grafted na...

Polypeptide-Solvent Interactions Measured by Single Molecule Force Spectroscopy

AbstractStimulus-responsive biomolecules have attracted a large research interest because of their potential application in various areas such as drug delivery, actuators and sensing devices at the nanoscale. Using single-molecule force spectroscopy (SMFS) we studied elastin-like polypeptides (ELPs). These stimulus-responsive polypeptides undergo an inverse temperature transition, accompanied by a large conformational change, when the solvent quality is changed by increasing the temperature or by addition of salt. Understanding the relationship between peptide sequence and mechanisms of force generation can provide a route to engineer ELPs with desirable mechano-chemical properties. Here we studied the effect of solvent quality and type of guest residue on the mechanical properties of ELPs on the single-molecule level. We used a statistical approach to estimate polymer elasticity parameters from model fits to the data. With this approach we were able to resolve small changes in the Kuhn segment length distributions associated with different molecular architectures. We then show that these mechanical differences likely arise from differences in the hydrophobic hydration of sidegoups, in line with recent predictions from molecular dynamics simulations.

Permeability and Separation Characteristics of Polypeptide-Functionalized Polycarbonate Track-Etched Membranes

The use of polypeptide-functionalized membranes with known porosity and uniform pore sizes allows a better understanding of the separation characteristics in nanodomains. A stimuli-responsive polypeptide, poly-l-glutamic acid (PLGA), was immobilized on a polycarbonate track-etched (PCTE) membrane. First, PCTE membrane was gold-coated under convective conditions, and a thiol, 3-mercapto 1,2-propanediol (MPD), was chemisorbed on the modified surface. Second, the MPD molecule was oxidized with sodium periodate to obtain an aldehyde functionality, which was further reacted with the amino group on the PLGA molecule, making possible a single point polypeptide attachment. The morphology of the modified membrane was analyzed by electron microscopy (SEM, TEM) imaging, confirming uniform structure. Modified membrane performances, with starting diameters of 30 and 100 nm, were evaluated in terms of solute (ionic and neutral) rejections and water permeability. Both solute and water transport through membrane were rev...

Stimuli-responsive polypeptide vesicles by conformation-specific assembly.

In biology, lipids are well known for their ability to assemble into spherical vesicles. Proteins, in particular virus capsids, can also form regular vesicle-like structures, where the precise folding and stable conformations of many identical subunits directs their self-assembly. Functionality present on these subunits also controls their disassembly within the cellular environment, for example, in response to a pH change. Here, we report the preparation of diblock copolypeptides that self-assemble into spherical vesicular assemblies whose size and structure are dictated primarily by the ordered conformations of the polymer segments, in a manner similar to viral capsid assembly. Furthermore, functionality was incorporated into these molecules to render them susceptible to environmental stimuli, which is desirable for drug-delivery applications. The control of assembly and function exhibited in these systems is a significant advance towards the synthesis of materials that can mimic the precise three-dimensional assembly found in proteins.

Fabrication of a reversible protein array directly from cell lysate using a stimuli-responsive polypeptide.

We report a new method to reversibly bind proteins to a surface in a functionally active orientation directly from cell lysate by exploiting a thermodynamically reversible hydrophilic-hydrophobic lower critical solution temperature (LCST) transition exhibited by a recombinant, stimuli-responsive elastin-like polypeptide (ELP). An ELP is covalently micropatterned on a glass surface against an inert BSA background. The ELP-patterned surface is incubated with the soluble fraction of E. coli lysate containing an expressed ELP fusion protein, which is appended with the same ELP as on the surface. The LCST transition of the grafted ELP and the ELP fusion protein is simultaneously triggered by an external stimulus. The LCST transition results in capture of the ELP fusion protein from solution onto the immobilized ELP by hydrophobic interactions between the grafted ELP and the ELP fusion protein. The captured ELP fusion protein is oriented such that the fusion partner is accessible to binding of its target from solution. We also demonstrate that TRAP is reversible; the bound protein-ligand complex is released from the surface by reversing the LCST transition. The triggered control of interfacial properties provided by an immobilized stimuli-responsive polypeptide at the solid-water interface is an enabling technology that allows reversible and functional presentation of ELP fusion proteins on a surface directly from cell lysate without the necessity of intermediate purification steps and subsequent recovery of the protein-ligand complex for downstream analysis by other analytical techniques. TRAP has application in lab-on-a-chip bioanalytical devices as well as in the fabrication of peptide and protein arrays.