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Çalbaş B, Keobounnam AN, Korban C, Doratan AJ, Jean T, Sharma AY, Wright TA. Protein-polymer bioconjugation, immobilization, and encapsulation: a comparative review towards applicability, functionality, activity, and stability. Biomater Sci 2024; 12:2841-2864. [PMID: 38683585 DOI: 10.1039/d3bm01861j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/01/2024]
Abstract
Polymer-based biomaterials have received a lot of attention due to their biomedical, agricultural, and industrial potential. Soluble protein-polymer bioconjugates, immobilized proteins, and encapsulated proteins have been shown to tune enzymatic activity, improved pharmacokinetic ability, increased chemical and thermal stability, stimuli responsiveness, and introduced protein recovery. Controlled polymerization techniques, increased protein-polymer attachment techniques, improved polymer surface grafting techniques, controlled polymersome self-assembly, and sophisticated characterization methods have been utilized for the development of well-defined polymer-based biomaterials. In this review we aim to provide a brief account of the field, compare these methods for engineering biomaterials, provide future directions for the field, and highlight impacts of these forms of bioconjugation.
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Affiliation(s)
- Berke Çalbaş
- Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA, USA.
| | - Ashley N Keobounnam
- Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA, USA.
| | - Christopher Korban
- Department of Bioengineering, University of California, Los Angeles, Los Angeles, CA, USA
| | - Ainsley Jade Doratan
- Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA, USA.
| | - Tiffany Jean
- Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA, USA.
| | - Aryan Yashvardhan Sharma
- Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA, USA.
| | - Thaiesha A Wright
- Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA, USA.
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2
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Sánchez-Morán H, Kaar JL, Schwartz DK. Combinatorial High-Throughput Screening of Complex Polymeric Enzyme Immobilization Supports. J Am Chem Soc 2024; 146:9112-9123. [PMID: 38500441 DOI: 10.1021/jacs.3c14273] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/20/2024]
Abstract
Recent advances have demonstrated the promise of complex multicomponent polymeric supports to enable supra-biological enzyme performance. However, the discovery of such supports has been limited by time-consuming, low-throughput synthesis and screening. Here, we describe a novel combinatorial and high-throughput platform that enables rapid screening of complex and heterogeneous copolymer brushes as enzyme immobilization supports, named combinatorial high-throughput enzyme support screening (CHESS). Using a 384-well plate format, we synthesized arrays of three-component polymer brushes in the microwells using photoactivated surface-initiated polymerization and immobilized enzymes in situ. The utility of CHESS to identify optimal immobilization supports under thermally and chemically denaturing conditions was demonstrated usingBacillus subtilisLipase A (LipA). The identification of supports with optimal compositions was validated by immobilizing LipA on polymer-brush-modified biocatalyst particles. We further demonstrated that CHESS could be used to predict the optimal composition of polymer brushes a priori for the previously unexplored enzyme, alkaline phosphatase (AlkP). Our findings demonstrate that CHESS represents a predictable and reliable platform for dramatically accelerating the search of chemical compositions for immobilization supports and further facilitates the discovery of biocompatible and stabilizing materials.
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Affiliation(s)
- Héctor Sánchez-Morán
- Department of Chemical and Biological Engineering, University of Colorado, Campus Box 596, Boulder, Colorado 80309, United States
| | - Joel L Kaar
- Department of Chemical and Biological Engineering, University of Colorado, Campus Box 596, Boulder, Colorado 80309, United States
| | - Daniel K Schwartz
- Department of Chemical and Biological Engineering, University of Colorado, Campus Box 596, Boulder, Colorado 80309, United States
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3
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Sánchez-Morán H, Kaar JL, Schwartz DK. Supra-biological performance of immobilized enzymes enabled by chaperone-like specific non-covalent interactions. Nat Commun 2024; 15:2299. [PMID: 38485940 PMCID: PMC10940687 DOI: 10.1038/s41467-024-46719-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Accepted: 03/01/2024] [Indexed: 03/18/2024] Open
Abstract
Designing complex synthetic materials for enzyme immobilization could unlock the utility of biocatalysis in extreme environments. Inspired by biology, we investigate the use of random copolymer brushes as dynamic immobilization supports that enable supra-biological catalytic performance of immobilized enzymes. This is demonstrated by immobilizing Bacillus subtilis Lipase A on brushes doped with aromatic moieties, which can interact with the lipase through multiple non-covalent interactions. Incorporation of aromatic groups leads to a 50 °C increase in the optimal temperature of lipase, as well as a 50-fold enhancement in enzyme activity. Single-molecule FRET studies reveal that these supports act as biomimetic chaperones by promoting enzyme refolding and stabilizing the enzyme's folded and catalytically active state. This effect is diminished when aromatic residues are mutated out, suggesting the importance of π-stacking and π-cation interactions for stabilization. Our results underscore how unexplored enzyme-support interactions may enable uncharted opportunities for using enzymes in industrial biotransformations.
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Affiliation(s)
- Héctor Sánchez-Morán
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Campus Box 596, Boulder, CO, 80309, USA
| | - Joel L Kaar
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Campus Box 596, Boulder, CO, 80309, USA.
| | - Daniel K Schwartz
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Campus Box 596, Boulder, CO, 80309, USA.
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4
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Sánchez-Morán H, Gonçalves LRB, Schwartz DK, Kaar JL. Framework for Optimizing Polymeric Supports for Immobilized Biocatalysts by Computational Analysis of Enzyme Surface Hydrophobicity. ACS Catal 2023. [DOI: 10.1021/acscatal.3c00264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/17/2023]
Affiliation(s)
- Héctor Sánchez-Morán
- Department of Chemical and Biological Engineering, University of Colorado, Campus Box 596, Boulder, Colorado 80309, United States
| | - Luciana Rocha Barros Gonçalves
- Department of Chemical Engineering, Federal University of Ceará, Campus do Pici, Bloco 709, Fortaleza, Ceará CEP 60455-760, Brazil
| | - Daniel K. Schwartz
- Department of Chemical and Biological Engineering, University of Colorado, Campus Box 596, Boulder, Colorado 80309, United States
| | - Joel L. Kaar
- Department of Chemical and Biological Engineering, University of Colorado, Campus Box 596, Boulder, Colorado 80309, United States
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5
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Reichelderfer VT, Chaparro Sosa AF, Kaar JL, Schwartz DK. Tuning the surface charge of phospholipid bilayers inhibits insulin fibrilization. Colloids Surf B Biointerfaces 2022; 220:112904. [PMID: 36265317 PMCID: PMC10164472 DOI: 10.1016/j.colsurfb.2022.112904] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2022] [Revised: 09/27/2022] [Accepted: 10/02/2022] [Indexed: 11/27/2022]
Abstract
The interactions between proteins and materials, in particular lipid bilayers, have been studied extensively for their relevance in diseases and for the formulation of protein-based therapeutics and vaccines. However, the precise rules by which material properties induce favorable or unfavorable structural states in biomolecules are incompletely understood, and as a result, the rational design of materials remains challenging. Here, we investigated the influence of lipid bilayers (in the form of small unilamellar vesicles) on the formation of insulin amyloid fibrils using a fibril-specific assay (thioflavin T), polyacrylamide gel electrophoresis, and circular dichroism spectroscopy. Lipid bilayers composed of equal mixtures of cationic and anionic lipids effectively inhibited fibril formation and stabilized insulin in its native conformation. However, other lipid bilayer compositions failed to inhibit fibril formation or even destabilized insulin, exacerbating fibrilization and/or non-amyloid aggregation. Our findings suggest that electrostatic interactions with lipid bilayers can play a critical role in stabilizing or destabilizing insulin, and preventing the conversion of insulin to its amyloidogenic, disease-associated state.
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Affiliation(s)
- Victoria T Reichelderfer
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309, USA
| | - Andres F Chaparro Sosa
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309, USA
| | - Joel L Kaar
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309, USA.
| | - Daniel K Schwartz
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309, USA.
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Wu D, Lv P, Feng Q, Jiang Y, Yang H, Alfred M, Wei Q. Biomass-derived nanocellulose aerogel enable highly efficient immobilization of laccase for the degradation of organic pollutants. BIORESOURCE TECHNOLOGY 2022; 356:127311. [PMID: 35569713 DOI: 10.1016/j.biortech.2022.127311] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2022] [Revised: 05/08/2022] [Accepted: 05/10/2022] [Indexed: 06/15/2023]
Abstract
Laccase is a promising biocatalyst for pollutant degradation and water purification. However, laccase can only improve the stability of enzyme activity and achieve its significant catalytic effect after effective immobilization. Herein, we report a general strategy to integrate nanocellulose aerogel and laccase for high-efficiency degradation of organic pollutants. Biomass-derived functional bacterial cellulose (BC) aerogel with a nanonetwork structure and high porosity was prepared by biosynthesis, solvent replacement, and atom transfer radical polymerization (ATRP) procedures. Subsequently, a biocatalyst platform was fabricated by "coupling" ATRP-modified BC aerogel with abundant active sites with laccase through ion coordination. The results demonstrated the biocatalyst platform not only has good biological affinity, but also has high enzyme load and structural stability. Meanwhile, the degradation rates of reactive red X-3B and 2, 4-dichlorophenol reached 94.5% and 85.2% within 4 h, respectively. The strategy disclosed herein could provide a practical method for the degradation of organic pollutants.
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Affiliation(s)
- Dingsheng Wu
- Key Laboratory of Textile Fabrics, College of Textiles and Clothing, Anhui Polytechnic University, Wuhu, Anhui 241000, PR China; Key Laboratory of Eco-Textiles, Ministry of Education, Jiangnan University, Wuxi, Jiangsu 214122, PR China
| | - Pengfei Lv
- Key Laboratory of Eco-Textiles, Ministry of Education, Jiangnan University, Wuxi, Jiangsu 214122, PR China
| | - Quan Feng
- Key Laboratory of Textile Fabrics, College of Textiles and Clothing, Anhui Polytechnic University, Wuhu, Anhui 241000, PR China
| | - Yu Jiang
- School of Pharmacy, Nantong University, Nantong, Jiangsu 226001, PR China
| | - Hanrui Yang
- Key Laboratory of Eco-Textiles, Ministry of Education, Jiangnan University, Wuxi, Jiangsu 214122, PR China
| | - Mensah Alfred
- Key Laboratory of Textile Fabrics, College of Textiles and Clothing, Anhui Polytechnic University, Wuhu, Anhui 241000, PR China
| | - Qufu Wei
- Key Laboratory of Eco-Textiles, Ministry of Education, Jiangnan University, Wuxi, Jiangsu 214122, PR China.
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7
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Gabriunaite I, Valiuniene A, Ramanavicius S, Ramanavicius A. Biosensors Based on Bio-Functionalized Semiconducting Metal Oxides. Crit Rev Anal Chem 2022; 54:549-564. [PMID: 35714203 DOI: 10.1080/10408347.2022.2088226] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Immobilization of biomaterials is a very important task in the development of biofuel cells and biosensors. Some semiconducting metal-oxide-based supporting materials can be used in these bioelectronics-based devices. In this article, we are reviewing some functionalization methods that are applied for the immobilization of biomaterials. The most significant attention is paid to the immobilization of biomolecules on the surface of semiconducting metal oxides. The improvement of biomaterials immobilization on metal oxides and analytical performance of biosensors by coatings based on conducting polymers, self-assembled monolayers and lipid membranes is discussed.
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Affiliation(s)
- Inga Gabriunaite
- Vilnius University, Faculty of Chemistry and Geosciences, Institute of Chemistry, Department of Physical Chemistry, Vilnius, Lithuania
| | - Ausra Valiuniene
- Vilnius University, Faculty of Chemistry and Geosciences, Institute of Chemistry, Department of Physical Chemistry, Vilnius, Lithuania
| | - Simonas Ramanavicius
- Centre for Physical Sciences and Technology, Department of Electrochemical Material Science, Vilnius, Lithuania
| | - Arunas Ramanavicius
- Vilnius University, Faculty of Chemistry and Geosciences, Institute of Chemistry, Department of Physical Chemistry, Vilnius, Lithuania
- Centre for Physical Sciences and Technology, Department of Electrochemical Material Science, Vilnius, Lithuania
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8
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Velasco Abadia A, Herbert KM, Matavulj VM, White TJ, Schwartz DK, Kaar JL. Chemically Triggered Changes in Mechanical Properties of Responsive Liquid Crystal Polymer Networks with Immobilized Urease. J Am Chem Soc 2021; 143:16740-16749. [PMID: 34590861 DOI: 10.1021/jacs.1c08216] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Liquid crystal polymer networks (LCNs) are stimuli-responsive materials that can be programmed to realize spatial variation in mechanical response and undergo shape transformation. Herein, we report a process to introduce chemical specificity to the stimuli response of LCNs by integrating enzymes as molecular triggers. Specifically, the enzyme urease was immobilized in LCN films via acyl fluoride conjugation chemistry. Activity assays and confocal fluorescence imaging confirmed retention of urease activity after immobilization as well as widespread distribution of enzyme on the film. The addition of urea triggered a response in the LCN whereby newly generated ammonia reacted with free acyl fluorides to form benzamide moieties. These moieties were capable of dimerizing through the formation of supramolecular hydrogen bonds, which was reflected in a 4-fold increase in Young's modulus. Through dynamic mechanical analysis and calorimetry, we further confirmed that the degree of hydrogen bonding in the LCNs could be judiciously designed to fine-tune the mechanical properties and glass transition temperature. These findings demonstrate the untapped potential of biochemical mechanisms as molecular triggers in LCNs and open the door to the use of nucleophilic chemistries in modulating the mechanical properties of LCNs.
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Affiliation(s)
- Albert Velasco Abadia
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Katie M Herbert
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Valentina M Matavulj
- Material Science and Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Timothy J White
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States
- Material Science and Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Daniel K Schwartz
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Joel L Kaar
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States
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9
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Sosa AFC, Bednar RM, Mehl RA, Schwartz DK, Kaar JL. Faster Surface Ligation Reactions Improve Immobilized Enzyme Structure and Activity. J Am Chem Soc 2021; 143:7154-7163. [PMID: 33914511 PMCID: PMC8574164 DOI: 10.1021/jacs.1c02375] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
During integration into materials, the inactivation of enzymes as a result of their interaction with nanometer size denaturing "hotspots" on surfaces represents a critical challenge. This challenge, which has received far less attention than improving the long-term stability of enzymes, may be overcome by limiting the exploration of surfaces by enzymes. One way this may be accomplished is through increasing the rate constant of the surface ligation reaction and thus the probability of immobilization with reactive surface sites (i.e., ligation efficiency). Here, the connection between ligation reaction efficiency and the retention of enzyme structure and activity was investigated by leveraging the extremely fast reaction of strained trans-cyclooctene (sTCOs) and tetrazines (Tet). Remarkably, upon immobilization via Tet-sTCO chemistry, carbonic anhydrase (CA) retained 77% of its solution-phase activity, while immobilization via less efficient reaction chemistries, such as thiol-maleimide and azide-dibenzocyclooctyne, led to activity retention of only 46% and 27%, respectively. Dynamic single-molecule fluorescence tracking methods further revealed that longer surface search distances prior to immobilization (>0.5 μm) dramatically increased the probability of CA unfolding. Notably, the CA distance to immobilization was significantly reduced through the use of Tet-sTCO chemistry, which correlated with the increased retention of structure and activity of immobilized CA compared to the use of slower ligation chemistries. These findings provide an unprecedented insight into the role of ligation reaction efficiency in mediating the exploration of denaturing hotspots on surfaces by enzymes, which, in turn, may have major ramifications in the creation of functional biohybrid materials.
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Affiliation(s)
- Andres F. Chaparro Sosa
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309
| | - Riley M. Bednar
- Department of Biochemistry and Biophysics, Oregon State University, 2011 Agricultural & Life Sciences Building, Corvallis, OR 97331-7305
| | - Ryan A. Mehl
- Department of Biochemistry and Biophysics, Oregon State University, 2011 Agricultural & Life Sciences Building, Corvallis, OR 97331-7305
| | - Daniel K. Schwartz
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309
| | - Joel L. Kaar
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309
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10
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Thompson CJ, Vu VH, Leckband DE, Schwartz DK. Cadherin cis and trans interactions are mutually cooperative. Proc Natl Acad Sci U S A 2021; 118:e2019845118. [PMID: 33658369 PMCID: PMC7958404 DOI: 10.1073/pnas.2019845118] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Cadherin transmembrane proteins are responsible for intercellular adhesion in all biological tissues and modulate tissue morphogenesis, cell motility, force transduction, and macromolecular transport. The protein-mediated adhesions consist of adhesive trans interactions and lateral cis interactions. Although theory suggests cooperativity between cis and trans bonds, direct experimental evidence of such cooperativity has not been demonstrated. Here, the use of superresolution microscopy, in conjunction with intermolecular single-molecule Förster resonance energy transfer, demonstrated the mutual cooperativity of cis and trans interactions. Results further demonstrate the consequent assembly of large intermembrane junctions, using a biomimetic lipid bilayer cell adhesion model. Notably, the presence of cis interactions resulted in a nearly 30-fold increase in trans-binding lifetimes between epithelial-cadherin extracellular domains. In turn, the presence of trans interactions increased the lifetime of cis bonds. Importantly, comparison of trans-binding lifetimes of small and large cadherin clusters suggests that this cooperativity is primarily due to allostery. The direct quantitative demonstration of strong mutual cooperativity between cis and trans interactions at intermembrane adhesions provides insights into the long-standing controversy of how weak cis and trans interactions act in concert to create strong macroscopic cell adhesions.
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Affiliation(s)
- Connor J Thompson
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309
| | - Vinh H Vu
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, IL 61801
| | - Deborah E Leckband
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, IL 61801
- Department of Chemical and Biomolecular Engineering, University of Illinois Urbana-Champaign, Urbana, IL 61801
| | - Daniel K Schwartz
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309;
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11
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Grigolato F, Arosio P. The role of surfaces on amyloid formation. Biophys Chem 2021; 270:106533. [PMID: 33529995 DOI: 10.1016/j.bpc.2020.106533] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Revised: 12/18/2020] [Accepted: 12/18/2020] [Indexed: 01/02/2023]
Abstract
Interfaces can strongly accelerate or inhibit protein aggregation, destabilizing proteins that are stable in solution or, conversely, stabilizing proteins that are aggregation-prone. Although this behaviour is well-known, our understanding of the molecular mechanisms underlying surface-induced protein aggregation is still largely incomplete. A major challenge is represented by the high number of physico-chemical parameters involved, which are highly specific to the considered combination of protein, surface properties, and solution conditions. The key aspect determining the role of interfaces is the relative propensity of the protein to aggregate at the surface with respect to bulk. In this review, we discuss the multiple molecular determinants that regulate this balance. We summarize current experimental techniques aimed at characterizing protein aggregation at interfaces, and highlight the need to complement experimental analysis with theoretical modelling. In particular, we illustrate how chemical kinetic analysis can be combined with experimental methods to provide insights into the molecular mechanisms underlying surface-induced protein aggregation, under both stagnant and agitation conditions. We summarize recent progress in the study of important amyloids systems, focusing on selected relevant interfaces.
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Affiliation(s)
- Fulvio Grigolato
- Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering, ETH Zurich, Zurich 8093, Switzerland
| | - Paolo Arosio
- Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering, ETH Zurich, Zurich 8093, Switzerland.
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12
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Gehlen MH, Foltran LS, Kienle DF, Schwartz DK. Single-Molecule Observations Provide Mechanistic Insights into Bimolecular Knoevenagel Amino Catalysis. J Phys Chem Lett 2020; 11:9714-9724. [PMID: 33136415 DOI: 10.1021/acs.jpclett.0c03030] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
While single-molecule (SM) methods have provided new insights to various catalytic processes, bimolecular reactions have been particularly challenging to study. Here, the fluorogenic Knoevenagel condensation of an aromatic aldehyde with methyl cyanoacetate promoted by surface-immobilized piperazine is quantitatively characterized using super-resolution fluorescence imaging and stochastic analysis using hidden Markov modeling (HMM). Notably, the SM results suggest that the reaction follows the iminium intermediate pathway before the formation of a fluorescent product with intramolecular charge-transfer character. Moreover, the overall process is limited by the turnover rate of the catalyst, which is involved in multiple steps along the reaction coordinate.
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Affiliation(s)
- Marcelo H Gehlen
- Department of Physical Chemistry, Institute of Chemistry of São Carlos, University of São Paulo, 13566-590 São Carlos, SP, Brazil
| | - Larissa S Foltran
- Department of Physical Chemistry, Institute of Chemistry of São Carlos, University of São Paulo, 13566-590 São Carlos, SP, Brazil
| | - Daniel F Kienle
- Department of Chemistry and Biological Engineering, University of Colorado, Boulder, Colorado 80309, United States
| | - Daniel K Schwartz
- Department of Chemistry and Biological Engineering, University of Colorado, Boulder, Colorado 80309, United States
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13
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Immobilization of lipase AYS on UiO-66-NH2 metal-organic framework nanoparticles as a recyclable biocatalyst for ester hydrolysis and kinetic resolution. Sep Purif Technol 2020. [DOI: 10.1016/j.seppur.2020.117398] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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14
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Sosa AFC, de Olivera da Silva SM, Morgan GP, Schwartz DK, Kaar JL. Mixed Phospholipid Vesicles Catalytically Inhibit and Reverse Amyloid Fibril Formation. J Phys Chem Lett 2020; 11:7417-7422. [PMID: 32803986 PMCID: PMC10164471 DOI: 10.1021/acs.jpclett.0c02074] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
While many approaches to reduce fibrillation of amyloid-β (Aβ) have been aimed at slowing fibril formation, the degradation of fibrils remains challenging. We provide insight into fibril degradation as well as the inhibition of fiber formation by lipid vesicles composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine and 1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol). In the presence of vesicles with the optimal lipid composition, fibril formation was inhibited up to 76%. Additionally, by tuning the lipid composition, mature fibril content decreased up to 74% and the β-sheet content of Aβ was significantly reduced. The reduction in fibril and β-sheet content was consistent with a decrease in fibril diameter and could be attributed to the chaperone-like activity of the mixed vesicles. While demonstrating this remarkable activity, our findings present new evidence that lipid composition has a significant effect on the strength of the interaction between lipid bilayers and Aβ peptides/fibrils. This understanding has intriguing therapeutic implications in treating protein misfolding diseases.
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Affiliation(s)
- Andres F. Chaparro Sosa
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309
| | | | - Garry P. Morgan
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO, 80309
| | - Daniel K. Schwartz
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309
- Corresponding Authors: Daniel K. Schwartz, University of Colorado Boulder, Department of Chemical and Biological Engineering, Campus Box 596, Boulder, CO 80309, Tel: (303) 735-0240, Fax: (303) 492-4341, ; Joel L. Kaar, University of Colorado Boulder, Department of Chemical and Biological Engineering, Campus Box 596, Boulder, CO 80309, Tel: (303) 492-6031, Fax: (303) 492-4341,
| | - Joel L. Kaar
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309
- Corresponding Authors: Daniel K. Schwartz, University of Colorado Boulder, Department of Chemical and Biological Engineering, Campus Box 596, Boulder, CO 80309, Tel: (303) 735-0240, Fax: (303) 492-4341, ; Joel L. Kaar, University of Colorado Boulder, Department of Chemical and Biological Engineering, Campus Box 596, Boulder, CO 80309, Tel: (303) 492-6031, Fax: (303) 492-4341,
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15
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Thompson CJ, Su Z, Vu VH, Wu Y, Leckband DE, Schwartz DK. Cadherin clusters stabilized by a combination of specific and nonspecific cis-interactions. eLife 2020; 9:e59035. [PMID: 32876051 PMCID: PMC7505656 DOI: 10.7554/elife.59035] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Accepted: 09/01/2020] [Indexed: 12/13/2022] Open
Abstract
We demonstrate a combined experimental and computational approach for the quantitative characterization of lateral interactions between membrane-associated proteins. In particular, weak, lateral (cis) interactions between E-cadherin extracellular domains tethered to supported lipid bilayers, were studied using a combination of dynamic single-molecule Förster Resonance Energy Transfer (FRET) and kinetic Monte Carlo (kMC) simulations. Cadherins are intercellular adhesion proteins that assemble into clusters at cell-cell contacts through cis- and trans- (adhesive) interactions. A detailed and quantitative understanding of cis-clustering has been hindered by a lack of experimental approaches capable of detecting and quantifying lateral interactions between proteins on membranes. Here single-molecule intermolecular FRET measurements of wild-type E-cadherin and cis-interaction mutants combined with simulations demonstrate that both nonspecific and specific cis-interactions contribute to lateral clustering on lipid bilayers. Moreover, the intermolecular binding and dissociation rate constants are quantitatively and independently determined, demonstrating an approach that is generalizable for other interacting proteins.
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Affiliation(s)
- Connor J Thompson
- Department of Chemical and Biological Engineering, University of Colorado BoulderBoulderUnited States
| | - Zhaoqian Su
- Department of Systems and Computational Biology, Albert Einstein College of MedicineBronxUnited States
| | - Vinh H Vu
- Department of Biochemistry and University of Illinois, Urbana-ChampaignUrbanaUnited States
| | - Yinghao Wu
- Department of Systems and Computational Biology, Albert Einstein College of MedicineBronxUnited States
| | - Deborah E Leckband
- Department of Biochemistry and University of Illinois, Urbana-ChampaignUrbanaUnited States
- Department of Chemical and Biomolecular Engineering, University of Illinois, Urbana-ChampaignUrbanaUnited States
| | - Daniel K Schwartz
- Department of Chemical and Biological Engineering, University of Colorado BoulderBoulderUnited States
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Kienle DF, Chaparro Sosa AF, Kaar JL, Schwartz DK. Polyelectrolyte Multilayers Enhance the Dry Storage and pH Stability of Physically Entrapped Enzymes. ACS APPLIED MATERIALS & INTERFACES 2020; 12:22640-22649. [PMID: 32352745 DOI: 10.1021/acsami.0c04964] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Polyelectrolyte multilayers (PEMs) are attractive materials for immobilizing enzymes due to their unique ionic environment, which can prevent unfolding. Here, we demonstrated that the stability to dry storage and elevated pH were significantly enhanced when negatively charged nitroreductase (NfsB) was embedded in a PEM by depositing alternating layers of the enzyme and polycation (PC) onto porous silica particles. The PC strength (i.e., pKa) and the surface charge of the film were varied to probe the effects that internal and surface chemistry had on the pH stability of the entrapped NfsB. All films showed enhanced activity retention at elevated pH (>6), and inactivation at reduced pH (<6) similar to NfsB in solution, indicating that the primary stabilizing effect of immobilization was achieved through ionic interactions between NfsB and the PC and not through changes to the surface charge of the NfsB. Additionally, films that were stored dry at 4 °C for 1 month retained full activity, while those stored at room temperature lost 30% activity. Remarkably, at 50 °C, above the NfsB melting temperature, 40% activity was retained after 1 month of dry storage. Our results suggest that internal film properties are significantly more important than surface charge, which had minor effects on activity. Specifically, immobilization with the weak PC, poly(l-lysine), increased the optimal pH and the activity of immobilized NfsB (which we attribute to greater permeability), relative to immobilization with the strong PC, poly(diallyldimethylammonium chloride). However, NfsB was leached from the PLL film to a greater extent. Overall, these observations demonstrate that internal ionic cross-linking is key to the stabilizing effects of PEMs and that the pH response can be tuned by controlling the number of cross-links (e.g., by changing the strength of the PC). However, this may be at the cost of reduced loading, illustrating the necessity of simultaneously optimizing enzyme loading, internal ionic cross-linking, and substrate transport.
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Affiliation(s)
- Daniel F Kienle
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, United States
| | - Andres F Chaparro Sosa
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, United States
| | - Joel L Kaar
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, United States
| | - Daniel K Schwartz
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, United States
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17
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Torres M, Rosselló CA, Fernández-García P, Lladó V, Kakhlon O, Escribá PV. The Implications for Cells of the Lipid Switches Driven by Protein-Membrane Interactions and the Development of Membrane Lipid Therapy. Int J Mol Sci 2020; 21:ijms21072322. [PMID: 32230887 PMCID: PMC7177374 DOI: 10.3390/ijms21072322] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Revised: 03/17/2020] [Accepted: 03/19/2020] [Indexed: 02/06/2023] Open
Abstract
The cell membrane contains a variety of receptors that interact with signaling molecules. However, agonist-receptor interactions not always activate a signaling cascade. Amphitropic membrane proteins are required for signal propagation upon ligand-induced receptor activation. These proteins localize to the plasma membrane or internal compartments; however, they are only activated by ligand-receptor complexes when both come into physical contact in membranes. These interactions enable signal propagation. Thus, signals may not propagate into the cell if peripheral proteins do not co-localize with receptors even in the presence of messengers. As the translocation of an amphitropic protein greatly depends on the membrane's lipid composition, regulation of the lipid bilayer emerges as a novel therapeutic strategy. Some of the signals controlled by proteins non-permanently bound to membranes produce dramatic changes in the cell's physiology. Indeed, changes in membrane lipids induce translocation of dozens of peripheral signaling proteins from or to the plasma membrane, which controls how cells behave. We called these changes "lipid switches", as they alter the cell's status (e.g., proliferation, differentiation, death, etc.) in response to the modulation of membrane lipids. Indeed, this discovery enables therapeutic interventions that modify the bilayer's lipids, an approach known as membrane-lipid therapy (MLT) or melitherapy.
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Affiliation(s)
- Manuel Torres
- Laboratory of Molecular Cell Biomedicine, Department of Biology, University of the Balearic Islands, Ctra. de Valldemossa km 7.5, E-07122 Palma, Spain; (M.T.); (C.A.R.); (P.F.-G.); (V.L.)
- Department of R&D, Laminar Pharmaceuticals SL. ParcBit, Ed. Naorte B, E-07121 Palma, Spain
| | - Catalina Ana Rosselló
- Laboratory of Molecular Cell Biomedicine, Department of Biology, University of the Balearic Islands, Ctra. de Valldemossa km 7.5, E-07122 Palma, Spain; (M.T.); (C.A.R.); (P.F.-G.); (V.L.)
- Department of R&D, Laminar Pharmaceuticals SL. ParcBit, Ed. Naorte B, E-07121 Palma, Spain
| | - Paula Fernández-García
- Laboratory of Molecular Cell Biomedicine, Department of Biology, University of the Balearic Islands, Ctra. de Valldemossa km 7.5, E-07122 Palma, Spain; (M.T.); (C.A.R.); (P.F.-G.); (V.L.)
- Department of R&D, Laminar Pharmaceuticals SL. ParcBit, Ed. Naorte B, E-07121 Palma, Spain
| | - Victoria Lladó
- Laboratory of Molecular Cell Biomedicine, Department of Biology, University of the Balearic Islands, Ctra. de Valldemossa km 7.5, E-07122 Palma, Spain; (M.T.); (C.A.R.); (P.F.-G.); (V.L.)
- Department of R&D, Laminar Pharmaceuticals SL. ParcBit, Ed. Naorte B, E-07121 Palma, Spain
| | - Or Kakhlon
- Department of Neurology, Hadassah-Hebrew University Medical Center, Ein Kerem, 91120 Jerusalem, Israel;
| | - Pablo Vicente Escribá
- Laboratory of Molecular Cell Biomedicine, Department of Biology, University of the Balearic Islands, Ctra. de Valldemossa km 7.5, E-07122 Palma, Spain; (M.T.); (C.A.R.); (P.F.-G.); (V.L.)
- Correspondence:
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Weltz JS, Kienle DF, Schwartz DK, Kaar JL. Reduced Enzyme Dynamics upon Multipoint Covalent Immobilization Leads to Stability-Activity Trade-off. J Am Chem Soc 2020; 142:3463-3471. [DOI: 10.1021/jacs.9b11707] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Affiliation(s)
- James S. Weltz
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Daniel F. Kienle
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Daniel K. Schwartz
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Joel L. Kaar
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States
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19
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Bolivar JM, Nidetzky B. On the relationship between structure and catalytic effectiveness in solid surface-immobilized enzymes: Advances in methodology and the quest for a single-molecule perspective. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2019; 1868:140333. [PMID: 31778816 DOI: 10.1016/j.bbapap.2019.140333] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2019] [Revised: 11/05/2019] [Accepted: 11/22/2019] [Indexed: 12/31/2022]
Abstract
The integration of enzymes with solid materials is important in many biotechnological applications, including the use of immobilized enzymes for biocatalytic synthesis. The development of functional enzyme-material composites is restrained by the lack of molecular-level insight into the behavior of enzymes in confined, surface-near environments. Here, we review recent advances in surface-sensitive spectroscopic techniques that push boundaries for the determination of enzyme structure and orientation at the solid-liquid interface. We discuss recent evidence from single-molecule studies showing that analyses sensitive to the temporal and spatial heterogeneities in immobilized enzymes can succeed in disentangling the effects of conformational stability and active-site accessibility on activity. Different immobilization methods involve distinct trade-off between these effects, thus emphasizing the need for a holistic (systems) view of immobilized enzymes for the rational development of practical biocatalysts.
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Affiliation(s)
- Juan M Bolivar
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Petersgasse 12, A-8010 Graz, Austria; Austrian Centre of Industrial Biotechnology, Petersgasse 12, A-8010 Graz, Austria; Chemical and Materials Engineering Department, Complutense University of Madrid, 28040 Madrid, Spain
| | - Bernd Nidetzky
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Petersgasse 12, A-8010 Graz, Austria; Austrian Centre of Industrial Biotechnology, Petersgasse 12, A-8010 Graz, Austria.
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20
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Faulón Marruecos D, Saleh LS, Kim HH, Bryant SJ, Schwartz DK, Kaar JL. Stabilization of Fibronectin by Random Copolymer Brushes Inhibits Macrophage Activation. ACS APPLIED BIO MATERIALS 2019; 2:4698-4702. [DOI: 10.1021/acsabm.9b00815] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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21
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Bull DS, Kienle DF, Chaparro Sosa AF, Nelson N, Roy S, Cha JN, Schwartz DK, Kaar JL, Goodwin AP. Surface-Templated Nanobubbles Protect Proteins from Surface-Mediated Denaturation. J Phys Chem Lett 2019; 10:2641-2647. [PMID: 31067058 PMCID: PMC8051143 DOI: 10.1021/acs.jpclett.9b00806] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
In this Letter, we report that surface-bound nanobubbles reduce protein denaturation on methylated glass by irreversible protein shell formation. Single-molecule total internal reflection fluorescence (SM-TIRF) microscopy was combined with intramolecular Förster resonance energy transfer (FRET) to study the conformational dynamics of nitroreductase (NfsB) on nanobubble-laden methylated glass surfaces, using reflection brightfield microscopy to register nanobubble locations with NfsB adsorption. First, NfsB adsorbed irreversibly to nanobubbles with no apparent desorption after 5 h. Moreover, virtually all (96%) of the NfsB molecules that interacted with nanobubbles remained folded, whereas less than 50% of NfsB molecules remained folded in the absence of nanobubbles on unmodified silica or methylated glass surfaces. This trend was confirmed by ensemble-average fluorometer TIRF experiments. We hypothesize that nanobubbles reduce protein damage by passivating strongly denaturing topographical surface defects. Thus, nanobubble stabilization on surfaces may have important implications for antifouling surfaces and improving therapeutic protein storage.
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Weltz JS, Kienle DF, Schwartz DK, Kaar JL. Dramatic Increase in Catalytic Performance of Immobilized Lipases by Their Stabilization on Polymer Brush Supports. ACS Catal 2019. [DOI: 10.1021/acscatal.9b01176] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- James S. Weltz
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, United States
| | - Daniel F. Kienle
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, United States
| | - Daniel K. Schwartz
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, United States
| | - Joel L. Kaar
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, United States
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23
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Meleleo D, Sblano C. Influence of cholesterol on human calcitonin channel formation. Possible role of sterol as molecular chaperone. AIMS BIOPHYSICS 2019. [DOI: 10.3934/biophy.2019.1.23] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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Plaks JG, Kaar JL. Lipoic Acid Ligase-Promoted Bioorthogonal Protein Modification and Immobilization. Methods Mol Biol 2019; 2012:279-297. [PMID: 31161513 DOI: 10.1007/978-1-4939-9546-2_14] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Protein bioconjugation benefits from precise regional and temporal control. One notable way of achieving this control is through the enzymatic attachment of bioorthogonal reactive handles to peptide recognition sequences that are genetically fused to target proteins of interest. The lipoic acid ligase variant, LplAW37V, functionalizes proteins by covalently attaching an azide-bearing lipoic acid derivative to a 13-amino acid recognition sequence known as the lipoic acid ligase acceptor peptide (LAP). Once attached, the azide group can be modified with diverse chemical entities through azide-alkyne click chemistry, enabling conjugation of chemical probes such as fluorophores and facilitating polymer attachment, glycosylation, and protein immobilization in addition to many other possible chemical modifications. The versatility of the attached azide group is complemented by the modular nature of the LAP sequence, which can be introduced within a protein at internal and/or terminal sites as well as at multiple sites simultaneously. In this chapter we describe the in vitro LplAW37V-mediated ligation of 10-azidodecanoic acid to a LAP-containing target protein (i.e., green fluorescent protein (GFP)) and the characterization of the ligation reaction products. Additionally, methods for the modification and immobilization of azide-functionalized LAP-GFP are discussed.
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Affiliation(s)
- Joseph G Plaks
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO, USA
| | - Joel L Kaar
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO, USA.
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Kienle DF, Falatach RM, Kaar JL, Schwartz DK. Correlating Structural and Functional Heterogeneity of Immobilized Enzymes. ACS NANO 2018; 12:8091-8103. [PMID: 30067333 DOI: 10.1021/acsnano.8b02956] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Many nanobiotechnology applications rely on stable and efficient integration of functional biomacromolecules with synthetic nanomaterials. Unfortunately, the reasons for the ubiquitous loss of activity of immobilized enzymes remain poorly understood due to the difficulty in distinguishing between distinct molecular-level mechanisms. Here, we employ complementary single-molecule fluorescence methods that independently measure the impact of immobilization on the structure and function ( i. e., substrate binding kinetics) of nitroreductase (NfsB). Stochastic statistical modeling methods were used to unambiguously quantify the effects of immobilized NfsB structural dynamics on function, allowing us to explicitly separate effects due to conformation and accessibility. Interestingly, we found that nonspecifically tethered NfsB exhibited enhanced stability compared to site-specifically tethered NfsB; however, the folded state of site-specifically tethered NfsB had faster substrate binding rates, suggesting improved active site accessibility. This demonstrated an unexpected intrinsic trade-off associated with competing bioconjugation methods, suggesting that it may be necessary to balance conformational stability versus active site accessibility. This nuanced view of the impact of immobilization will facilitate a rational approach to the integration of enzymes with synthetic nanomaterials.
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Affiliation(s)
- Daniel F Kienle
- Department of Chemical and Biological Engineering , University of Colorado , Boulder , Colorado 80309 , United States
| | - Rebecca M Falatach
- Department of Chemical and Biological Engineering , University of Colorado , Boulder , Colorado 80309 , United States
| | - Joel L Kaar
- Department of Chemical and Biological Engineering , University of Colorado , Boulder , Colorado 80309 , United States
| | - Daniel K Schwartz
- Department of Chemical and Biological Engineering , University of Colorado , Boulder , Colorado 80309 , United States
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