Biomedical subjects

Kristi L Kiick

Publications and source records attributed to Kristi L Kiick.

10 recordsLinked to original sources

PubMed2006

Manipulation of hydrogel assembly and growth factor delivery via the use of peptide-polysaccharide interactions.

The design of materials in which assembly, mechanical response, and biological properties are controlled by protein-polysaccharide interactions could provide materials that mimic the biological environment and find use in the delivery of growth factors. In the investigations reported here, a heparin-binding, coiled-coil peptide, PF4 ZIP, was employed to mediate the assembly of heparinized polymers. The heparin-binding affinity of this peptide was compared with that of other heparin-binding peptides (HBP) via heparin-sepharose chromatography and surface plasmon resonance (SPR) experiments. Results from these experiments indicate that PF4 ZIP demonstrates a higher heparin-binding affinity and heparin association rate when compared to the heparin-binding domains of antithrombin III (ATIII) and heparin-interacting protein (HIP). Viscoelastic hydrogels were formed upon the association of PF4 ZIP-functionalized star poly(ethylene glycol) (PEG-PF4 ZIP) with low-molecular-weight heparin-functionalized star PEG (PEG-LMWH). The viscoelastic properties of the hydrogels can be altered via variations in the ratio of LMWH to PF4 ZIP. bFGF release from these gels have also been investigated. Comparison of the bFGF release profiles with the hydrogel erosion profiles indicates that bFGF delivery from this class of hydrogels is mainly an erosion-controlled process and the rates of bFGF release can be modulated via choice of HBP or via variations in the mechanical properties of the hydrogels. Manipulation of hydrogel physical properties and erosion profiles will provide novel materials for controlled growth factor delivery and other biomedical applications.

Algorithms↗

PubMed2006

Effects of polymer structure on the inhibition of cholera toxin by linear polypeptide-based glycopolymers.

A variety of important biological events are mediated by the multivalent interaction between relevant oligosaccharides and multiple saccharide receptors on lectins, toxins, and cell surfaces; a variety of glycopolymeric materials have therefore been investigated in studies aimed at manipulating these events. The synthesis of protein- and polypeptide-based glycopolymers via protein engineering and other methods offers opportunities to control both the number and the spacing of saccharides on a scaffold, as well as the conformation of the polymer backbone, and will therefore facilitate the structure-based design of polymers for inhibition of multivalent binding events. In initial studies, we have synthesized a family of galactose-functionalized glycopolymers with a poly(L-glutamic acid) backbone, in which the density and linker length of the pendant carbohydrate moiety were varied. The composition of the glycopolymers was determined via (1)H NMR spectroscopy, and the impact of saccharide density and linker length, as well as the potential for these polypeptide-based glycopolymers to act as high-affinity inhibitors of the cholera toxin, has been indicated via competitive enzyme-linked immunosorbent assay and fluorescence titration experiments. The results of these studies suggest strategies for optimizing the binding of linear glycopolymers to bacterial toxins and will aid in the design of additional protein-based materials for studying the impact of multivalency, spacing, and backbone rigidity in a variety of biologically relevant binding events.

Cholera Toxin↗

PubMed2006

Conformation and assembly of polypeptide scaffolds in templating the synthesis of silica: an example of a polylysine macromolecular "switch".

Although the role of polycationic macromolecules in catalyzing the synthesis of silica structures is well established, detailed understanding of the mechanisms behind the production of silica structures of controlled morphologies remains unclear. In this study, we have used both poly-L-lysine (PLL) and/or poly-D-lysine (PDL) for silica synthesis to investigate mechanisms controlling inorganic morphologies. The formation of both spherical silica particles and hexagonal plates was observed. The formation of hexagonal plates was suggested, via circular dichroic spectroscopy (CD), to result from the assembly of helical polylysine molecules. We confirm that the formation of PLL helices is a prerequisite to the hexagonal silica synthesis. In addition, we present for the first time that the handedness of the helicity of the macromolecule does not affect the formation of hexagonal silica. We also show, by using two different silica precursors, that the precursor does not have a direct effect on the formation of hexagonal silica plates. Furthermore, when polylysine helices were converted to beta-sheet structure, only silica particles were obtained, thus suggesting that the adoption of a helical conformation by PLL is required for the formation of hexagonally organized silica. These results demonstrate that the change in polylysine conformation can act as a "switch" in silica structure formation and suggest the potential for controlling morphologies and structures of inorganic materials via control of the conformation of soft macromolecular templates.

Circular Dichroism↗

PubMed2005

Monodisperse protein-based glycopolymers via a combined biosynthetic and chemical approach.

Helical protein polymers with sequences comprising primarily alanine and glutamine have been designed to contain glutamic acid residues at distances that are targeted to match the receptor spacing of certain toxins and lectins. These proteins are readily expressed and purified from E. coli and are highly helical under a variety of solution conditions. The helical artificial proteins are also competent for chemical modification with saccharides for inhibition of select bacterial toxins and lectins. In the investigations reported here, multivalent artificial glycoproteins bearing galactose moieties as pendant groups have been prepared via the coupling reaction of amine-functionalized galactose with the glutamic acid functional groups of the protein polymer. Glycosylation of proteins was confirmed via mass spectrometry, NMR spectroscopy, SDS-PAGE, and photometric methods. CD spectroscopy shows that the resulting glycosylated proteins maintain a highly helical structure, and competitive ELISA assays suggest the efficient binding of these glycoproteins to cholera toxin. These results demonstrate that the integration of biological and chemical approaches in the synthesis of well-defined polymeric structures offers significant opportunities in the purposeful design of glycopolymers for applications in biology.

Amino Acid Sequence↗

PubMed2001

Incorporation of azides into recombinant proteins for chemoselective modification by the Staudinger ligation.

The introduction of chemically unique groups into proteins by means of non-natural amino acids has numerous applications in protein engineering and functional studies. One method to achieve this involves the utilization of a non-natural amino acid by the cell's native translational apparatus. Here we demonstrate that a methionine surrogate, azidohomoalanine, is activated by the methionyl-tRNA synthetase of Escherichia coli and replaces methionine in proteins expressed in methionine-depleted bacterial cultures. We further show that proteins containing azidohomoalanine can be selectively modified in the presence of other cellular proteins by means of Staudinger ligation with triarylphosphine reagents. Incorporation of azide-functionalized amino acids into proteins in vivo provides opportunities for protein modification under native conditions and selective labeling of proteins in the intracellular environment.

Animals↗

PubMedDate not supplied

Conformational behavior of chemically reactive alanine-rich repetitive protein polymers.

The synthesis of protein-based polymers with controlled conformational properties and functional group placement offers many opportunities for the design of advanced materials. In this work, protein engineering methods have been used to produce repetitive alanine-rich protein polymers with the sequence [(AAAQ)(5)(AAAE)(AAAQ)(5)](x) (x = 2 and 6); these macromolecules may mimic architectural features of certain alanine-rich helical sequences found in natural proteins. Various proteins from this family can be readily expressed and purified from Escherichia coli. Circular dichroic spectroscopy (CD) characterization demonstrates that the purified proteins are highly helical under a variety of conditions. Thermal analysis of [(AAAQ)(5)(AAAE)(AAAQ)(5)](2) via differential scanning calorimetry (DSC) and CD indicates that the protein undergoes a reversible helix-coil transition at approximately 45 degrees C and that the protein conformation can be manipulated at elevated temperatures depending on solution conditions. The demonstrated conformational properties of these artificial proteins suggest that they may be excellent candidates for elucidating structure-function relationships in biopolymers for nanotechnology and biological applications.

Alanine↗

PubMedDate not supplied

Effects of electrospinning and solution casting protocols on the secondary structure of a genetically engineered dragline spider silk analogue investigated via Fourier transform Raman spectroscopy.

Micrometer and submicrometer diameter fibers of recombinant dragline spider silk analogues, synthesized via protein engineering strategies, have been electrospun from 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and compared with cast films via Raman spectroscopy in order to assess changes in protein conformation that may result from the electrospinning process. Although the solvent casting process was shown to result in predominantly beta-sheet conformation similar to that observed in the bulk, the electrospinning process causes a major change in conformation from beta-sheet to alpha-helix. A possible mechanism involving electric field-induced stabilization of alpha-helical segments in HFIP solution during the electrospinning process is discussed.

Amino Acid Sequence↗

PubMedDate not supplied

Polysaccharide-poly(ethylene glycol) star copolymer as a scaffold for the production of bioactive hydrogels.

The production of polysaccharide-derivatized surfaces, polymers, and biomaterials has been shown to be a useful strategy for mediating the biological properties of materials, owing to the importance of polysaccharides for the sequestration and protection of bioactive proteins in vivo. We have therefore sought to combine the benefits of polysaccharide derivatization of polymers with unique opportunities to use these polymers for the production of bioactive, noncovalently assembled hydrogels. Accordingly, we report the synthesis of a heparin-modified poly(ethylene glycol) (PEG) star copolymer that can be used in the assembly of bioactive hydrogel networks via multiple strategies and that is also competent for the delivery of bioactive growth factors. A heparin-decorated polymer, synthesized by the reaction of thiol end-terminated four-arm star PEG (M(n) = 10 000) with maleimide functionalized low molecular weight heparin (LMWH, M(r) = 3000), has been characterized via (1)H NMR spectroscopy and size-exclusion chromatography; results indicate attachment of the LMWH with at least 73% efficiency. Both covalently and noncovalently assembled hydrogels can be produced from the PEG-LMWH conjugate. Viscoelastic noncovalently assembled hydrogels have been formed on the basis of the interaction of the PEG-LMWH with a PEG polymer bearing multiple heparin-binding peptide motifs. The binding and release of therapeutically important proteins from the assembled hydrogels have also been demonstrated via immunochemical assays, which demonstrate the slow release of basic fibroblast growth factor (bFGF) as a function of matrix erosion. The combination of these results suggests the opportunities for producing polymer-polysaccharide conjugates that can assemble into novel hydrogel networks on the basis of peptide-saccharide interactions and for employing these materials in delivery applications.

Amino Acid Sequence↗

PubMedDate not supplied

Rheological characterization of polysaccharide-poly(ethylene glycol) star copolymer hydrogels.

Binding interactions between low molecular weight heparin (LMWH) and heparin-binding peptides (HBP) have been applied as a strategy for the assembly of hydrogels that are capable of sequestering growth factors and delivering them in a controlled manner. In this work, the assembly of four-arm star poly(ethylene glycol) (PEG)-LMWH conjugate with PEG-HBP conjugates has been investigated. The interactions between LMWH and the heparin-binding regions of antithrombin III (ATIII) or the heparin interacting protein (HIP) have been characterized via heparin affinity chromatography and surface plasmon resonance (SPR); results indicate that the two peptides have slightly different affinities for heparin and LMWH, and bind LMWH with micromolar affinity. Solutions of the PEG-LMWH and of mixtures of the PEG-LMWH and PEG-HBP were characterized via both bulk rheology and laser tweezer microrheology. Interestingly, solutions of PEG-LMWH (2.5 wt % in PBS) form hydrogels in the absence of PEG-ATIII or PEG-HIP, with storage moduli, determined via bulk rheological measurements, in excess of the loss moduli over frequencies of 0.1-100 Hz. The addition of PEG-ATIII or PEG-HIP increases the moduli in direct proportion to the number of cross-links introduced. Characterization of the hydrogels via microrheology shows the gel microstructure is composed of polymer-rich fibrillar structures surrounded by polymer-depleted buffer. Potential applications of these hydrogels are discussed.

Amino Acid Sequence↗

PubMedDate not supplied

Functionalizing electrospun fibers with biologically relevant macromolecules.

The development of functionalized polymers that can elicit specific biological responses is of great interest in the biomedical community, as well as the development of methods to fabricate these biologically functionalized polymers. For example, the generation of fibrous matrices with biological properties and fiber diameters commensurate with those of the natural extracellular matrix (ECM) may permit the development of novel materials for use in wound healing or tissue engineering. The goal of this work is, therefore, to create a biologically active functionalized electrospun matrix to permit immobilization and long-term delivery of growth factors. In this work, poly(ethylene glycol) functionalized with low molecular weight heparin (PEG-LMWH) was fabricated into fibers for possible use in drug delivery, tissue engineering, or wound repair applications. Electrospinning was chosen to process the LMWH into fiber form due to the small fiber diameters and high degree of porosity that can be obtained relatively quickly and using small amounts of starting material. Both free LMWH and PEG-LMWH were investigated for their ability to be incorporated into electrospun fibers. Each of the samples were mixed with a carrier polymer consisting of either a 10 wt % poly(ethylene oxide) (PEO) or 45 wt % poly(lactide-co-glycolide) (PLGA). Field emission scanning electron microscopy (FESEM), energy-dispersive X-ray analysis (EDX), UV-vis spectroscopy, and multiphoton microscopy were used to characterize the electrospun matrices. The incorporation of heparin into the electrospun PEO and PLGA fibers did not affect the surface morphology or fiber diameters. The fibers produced had diameters ranging from approximately 100 to 400 nm. Toluidine blue assays of heparin suggest that it can be incorporated into an electrospun matrix at concentrations ranging from 3.5 to 85 mug per milligram of electrospun fibers. Multiphoton microscopy confirmed that incorporation of PEG-LMWH into the matrix permits retention of the heparin for at least 14 days. Improvements in the binding of basic fibroblast growth factor to the electrospun fibers were also observed for fibers functionalized with PEG-LMWH over those functionalized with LMWH alone. The combination of these results suggests the utility for producing electrospun fibers that are appropriately functionalized for use in biomaterials applications.

Coloring Agents↗