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Yagi S, Akanuma S, Kaji A, Niiro H, Akiyama H, Uchida T, Yamagishi A. Selection of a platinum-binding sequence in a loop of a four-helix bundle protein. J Biosci Bioeng 2017; 125:192-198. [PMID: 29050803 DOI: 10.1016/j.jbiosc.2017.09.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Revised: 09/01/2017] [Accepted: 09/20/2017] [Indexed: 10/18/2022]
Abstract
Protein-metal hybrids are functional materials with various industrial applications. For example, a redox enzyme immobilized on a platinum electrode is a key component of some biofuel cells and biosensors. To create these hybrid materials, protein molecules are bound to metal surfaces. Here, we report the selection of a novel platinum-binding sequence in a loop of a four-helix bundle protein, the Lac repressor four-helix protein (LARFH), an artificial protein in which four identical α-helices are connected via three identical loops. We created a genetic library in which the Ser-Gly-Gln-Gly-Gly-Ser sequence within the first inter-helical loop of LARFH was semi-randomly mutated. The library was then subjected to selection for platinum-binding affinity by using the T7 phage display method. The majority of the selected variants contained the Tyr-Lys-Arg-Gly-Tyr-Lys (YKRGYK) sequence in their randomized segment. We characterized the platinum-binding properties of mutant LARFH by using quartz crystal microbalance analysis. Mutant LARFH seemed to interact with platinum through its loop containing the YKRGYK sequence, as judged by the estimated exclusive area occupied by a single molecule. Furthermore, a 10-residue peptide containing the YKRGYK sequence bound to platinum with reasonably high affinity and basic side chains in the peptide were crucial in mediating this interaction. In conclusion, we have identified an amino acid sequence, YKRGYK, in the loop of a helix-loop-helix motif that shows high platinum-binding affinity. This sequence could be grafted into loops of other polypeptides as an approach to immobilize proteins on platinum electrodes for use as biosensors among other applications.
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Affiliation(s)
- Sota Yagi
- Department of Applied Life Science, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
| | - Satoshi Akanuma
- Faculty of Human Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa, Saitama 359-1192, Japan
| | - Asumi Kaji
- Department of Applied Life Science, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
| | - Hiroya Niiro
- Department of Applied Life Science, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
| | - Hayato Akiyama
- Department of Applied Life Science, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
| | - Tatsuya Uchida
- Department of Applied Life Science, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
| | - Akihiko Yamagishi
- Department of Applied Life Science, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan.
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Wibowo D, Yang GZ, Middelberg APJ, Zhao CX. Non-chromatographic bioprocess engineering of a recombinant mineralizing protein for the synthesis of silica nanocapsules. Biotechnol Bioeng 2016; 114:335-343. [PMID: 27543861 DOI: 10.1002/bit.26079] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2016] [Revised: 07/19/2016] [Accepted: 08/17/2016] [Indexed: 11/06/2022]
Abstract
Inspired by nature, synthetic mineralizing proteins have been developed to synthesize various structures of silica-based nanomaterials under environmentally friendly conditions. However, the development of bioprocesses able to assist in the translation of these new materials has lagged the development of the materials themselves. The development of cost-effective and scalable bioprocesses which minimize reliance on chromatography to recover biomolecules from microbial cell factories remains a significant challenge. This paper reports a simplified purification process for a recently reported recombinant catalytic modular (D4S2) protein (M(DPSMKQLADS-LHQLARQ-VSRLEHA)4 EPSRKKRKKRKKRKKGGGY; M 13.3 kDa; pI 10.9), which combines a variant of the established designer biosurfactant protein DAMP4 with a new biomimetic sequence (RKKRKKRKKRKKGGGY), providing for a bi-modular functionality (emulsification and biosilicification). The four-helix bundle structure of the protein has been demonstrated to remain stable and soluble under high temperature and high salt conditions, which confers simplified bioprocessing character. However, the high positive charge on the biosilification sequence necessitates removal of DNA contaminants from crude cell-extract at an early stage in the process by adding poly(ethyleneimine) (PEI). In this process, cellular protein contaminants were selectively precipitated by adding Na2 SO4 to the protein mixture up to a high concentration (1 M) and mixed at high temperature (90°C, 5 min) where D4S2 remained stable and soluble due to its four-helix bundle structure. Further increase of the Na2 SO4 concentration to 1.8 M precipitated, thus separated, D4S2 from residual PEI. The overall yield of the protein D4S2 was 28.8 mg per 800 mL cells (final cultivation OD600 ∼2) which gives an approximate 79% D4S2-protein yield. In comparison with the previously reported chromatographic purification of D4S2 protein (Wibowo et al., 2015), the final yield of D4S2 protein is increased fourfold in this study. The bio-produced protein D4S2 was proved to retain it emulsification and biosilicification functionalities enabling the formation of oil-core silica-shell nanocapsules at near-neutral pH and room temperature without the use of any toxic organic solvents, confirming no adverse effects due to bioprocess simplification. This work demonstrates that, through proper bioprocess engineering including the removal of critical contaminants such as DNA, a more efficient, simple, and scalable purification process can be used for the high-yield bio-production of a recombinant templating protein useful in the synthesis of bio-inspired nanomaterials. This simplified process is expected to be easily adapted to recover other mineralizing helix bundle-based functional proteins from microbial cell factories. Biotechnol. Bioeng. 2017;114: 335-343. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- David Wibowo
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia
| | - Guang-Ze Yang
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia
| | - Anton P J Middelberg
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia
| | - Chun-Xia Zhao
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia
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Yagi S, Akanuma S, Yamagishi M, Uchida T, Yamagishi A. De novo design of protein-protein interactions through modification of inter-molecular helix-helix interface residues. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2016; 1864:479-87. [PMID: 26867971 DOI: 10.1016/j.bbapap.2016.02.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Revised: 01/27/2016] [Accepted: 02/03/2016] [Indexed: 01/18/2023]
Abstract
For de novo design of protein-protein interactions (PPIs), information on the shape and chemical complementarity of their interfaces is generally required. Recent advances in computational PPI design have allowed for de novo design of protein complexes, and several successful examples have been reported. In addition, a simple and easy-to-use approach has also been reported that arranges leucines on a solvent-accessible region of an α-helix and places charged residues around the leucine patch to induce interactions between the two helical peptides. For this study, we adopted this approach to de novo design a new PPI between the helical bundle proteins sulerythrin and LARFH. A non-polar patch was created on an α-helix of LARFH around which arginine residues were introduced to retain its solubility. The strongest interaction found was for the LARFH variant cysLARFH-IV-3L3R and the sulerythrin mutant 6L6D (KD=0.16 μM). This artificial protein complex is maintained by hydrophobic and ionic interactions formed by the inter-molecular helical bundle structure. Therefore, by the simple and easy-to-use approach to create de novo interfaces on the α-helices, we successfully generated an artificial PPI. We also created a second LARFH variant with the non-polar patch surrounded by positively charged residues at each end. Upon mixing this LARFH variant with 6L6D, mesh-like fibrous nanostructures were observed by atomic force microscopy. Our method may, therefore, also be applicable to the de novo design of protein nanostructures.
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Affiliation(s)
- Sota Yagi
- Department of Applied Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
| | - Satoshi Akanuma
- Faculty of Human Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa, Saitama 359-1192, Japan
| | - Manami Yamagishi
- Department of Applied Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
| | - Tatsuya Uchida
- Department of Molecular Life Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
| | - Akihiko Yamagishi
- Department of Applied Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan.
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Wibowo D, Zhao CX, Middelberg APJ. Interfacial biomimetic synthesis of silica nanocapsules using a recombinant catalytic modular protein. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:1999-2007. [PMID: 25604437 DOI: 10.1021/la504684g] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
This paper reports interfacially driven synthesis of oil-core silica-shell nanocapsules using a rationally designed recombinant catalytic modular protein (ReCaMoP), in lieu of a conventional chemical surfactant. A 116-residue protein, D4S2, was designed by modularizing a surface-active protein module having four-helix bundle structure in bulk and a biosilicification-active peptide module rich in cationic residues. This modular combination design allowed the protein to be produced via the industrially relevant cell factory Escherichia coli with simplified purification conferred by thermostability engineered in design. Dynamic interfacial tension and thin film pressure balance were used to gain an overview of the protein behavior at macroscopic interfaces. Functionalities of D4S2 to make silica nanocapsules were demonstrated by facilitating formation and stabilization of pharmaceutically grade oil droplets through its surface-active module and then by directing nucleation and growth of a silica shell at the oil-water interface through its biosilicification-active module. Through these synergistic activities in D4S2, silica nanocapsules could be formed at near-neutral pH and ambient temperature without using any organic solvents that might have negative environmental and sustainability impacts. This work introduces parallelization of biomolecular, scale-up and interfacial catalytic design strategies for the ultimate development of sustainable and scalable production of a recombinant modular protein that is able to catalyze synthesis of oil-filled silica nanocapsules under environmentally friendly conditions, suitable for use as controlled-release nanocarriers of various actives in biomedical and agricultural applications.
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Affiliation(s)
- David Wibowo
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland , St. Lucia QLD 4072, Australia
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5
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Dimitrijev Dwyer M, Brech M, Yu L, Middelberg AP. Intensified expression and purification of a recombinant biosurfactant protein. Chem Eng Sci 2014. [DOI: 10.1016/j.ces.2013.10.024] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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6
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Kaur C, Vishnoi A, Ariyadasa TU, Bhattacharya A, Singla-Pareek SL, Sopory SK. Episodes of horizontal gene-transfer and gene-fusion led to co-existence of different metal-ion specific glyoxalase I. Sci Rep 2013; 3:3076. [PMID: 24220130 PMCID: PMC3826101 DOI: 10.1038/srep03076] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2013] [Accepted: 10/04/2013] [Indexed: 02/05/2023] Open
Abstract
Glyoxalase pathway plays an important role in stress adaptation and many clinical disorders. The first enzyme of this pathway, glyoxalase I (GlxI), uses methylglyoxal as a substrate and requires either Ni(II)/Co(II) or Zn(II) for activity. Here we have investigated the origin of different metal ion specificities of GlxI and subsequent pattern of inheritance during evolution. Our results suggest a primitive origin of single-domain Ni dependent GlxI [Ni-GlxI]. This subsequently evolved into Zn activated GlxI [Zn-GlxI] in deltaproteobacteria. However, origin of eukaryotic Zn-GlxI is different and can be traced to GlxI from Candidatus pelagibacter and Sphingomonas. In eukaryotes GlxI has evolved as two-domain protein but the corresponding Zn form is lost in plants/higher eukaryotes. In plants gene expansion has given rise to multiple two-domain Ni-GlxI which are differentially regulated under abiotic stress conditions. Our results suggest that different forms of GlxI have evolved to help plants adapt to stress.
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Affiliation(s)
- Charanpreet Kaur
- 1] International Centre for Genetic Engineering and Biotechnology Aruna Asaf Ali Marg 110 067 New Delhi, India [2] [3]
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Adachi M, Shimizu R, Kuroki R, Blaber M. Creation and structure determination of an artificial protein with three complete sequence repeats. JOURNAL OF SYNCHROTRON RADIATION 2013; 20:953-957. [PMID: 24121347 PMCID: PMC3795563 DOI: 10.1107/s0909049513022164] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Accepted: 08/07/2013] [Indexed: 06/02/2023]
Abstract
Symfoil-4P is a de novo protein exhibiting the threefold symmetrical β-trefoil fold designed based on the human acidic fibroblast growth factor. First three asparagine-glycine sequences of Symfoil-4P are replaced with glutamine-glycine (Symfoil-QG) or serine-glycine (Symfoil-SG) sequences protecting from deamidation, and His-Symfoil-II was prepared by introducing a protease digestion site into Symfoil-QG so that Symfoil-II has three complete repeats after removal of the N-terminal histidine tag. The Symfoil-QG and SG and His-Symfoil-II proteins were expressed in Eschericha coli as soluble protein, and purified by nickel affinity chromatography. Symfoil-II was further purified by anion-exchange chromatography after removing the HisTag by proteolysis. Both Symfoil-QG and Symfoil-II were crystallized in 0.1 M Tris-HCl buffer (pH 7.0) containing 1.8 M ammonium sulfate as precipitant at 293 K; several crystal forms were observed for Symfoil-QG and II. The maximum diffraction of Symfoil-QG and II crystals were 1.5 and 1.1 Å resolution, respectively. The Symfoil-II without histidine tag diffracted better than Symfoil-QG with N-terminal histidine tag. Although the crystal packing of Symfoil-II is slightly different from Symfoil-QG and other crystals of Symfoil derivatives having the N-terminal histidine tag, the refined crystal structure of Symfoil-II showed pseudo-threefold symmetry as expected from other Symfoils. Since the removal of the unstructured N-terminal histidine tag did not affect the threefold structure of Symfoil, the improvement of diffraction quality of Symfoil-II may be caused by molecular characteristics of Symfoil-II such as molecular stability.
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Affiliation(s)
- Motoyasu Adachi
- Molecular Structural Biology Group, Quantum Beam Science Directorate, Japan Atomic Energy Agency, Shirakatashirane 2-4, Nakagun Tokaimura, Ibaraki 319-1195, Japan
| | - Rumi Shimizu
- Molecular Structural Biology Group, Quantum Beam Science Directorate, Japan Atomic Energy Agency, Shirakatashirane 2-4, Nakagun Tokaimura, Ibaraki 319-1195, Japan
| | - Ryota Kuroki
- Molecular Structural Biology Group, Quantum Beam Science Directorate, Japan Atomic Energy Agency, Shirakatashirane 2-4, Nakagun Tokaimura, Ibaraki 319-1195, Japan
| | - Michael Blaber
- Molecular Structural Biology Group, Quantum Beam Science Directorate, Japan Atomic Energy Agency, Shirakatashirane 2-4, Nakagun Tokaimura, Ibaraki 319-1195, Japan
- Department of Biomedical Sciences, Florida State University, Tallahassee, FL 32306-4300, USA
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Fukuda M, Komatsu Y, Yamada H, Morikawa R, Miyakawa T, Takasu M, Akanuma S, Yamagishi A. Evaluation of the protein interfaces that form an intermolecular four-helix bundle as studied by computer simulation. MOLECULAR SIMULATION 2013. [DOI: 10.1080/08927022.2013.824571] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Doyle CM, Rumfeldt JA, Broom HR, Broom A, Stathopulos PB, Vassall KA, Almey JJ, Meiering EM. Energetics of oligomeric protein folding and association. Arch Biochem Biophys 2012; 531:44-64. [PMID: 23246784 DOI: 10.1016/j.abb.2012.12.005] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2012] [Revised: 11/29/2012] [Accepted: 12/05/2012] [Indexed: 12/11/2022]
Abstract
In nature, proteins most often exist as complexes, with many of these consisting of identical subunits. Understanding of the energetics governing the folding and misfolding of such homooligomeric proteins is central to understanding their function and misfunction, in disease or biotechnology. Much progress has been made in defining the mechanisms and thermodynamics of homooligomeric protein folding. In this review, we outline models as well as calorimetric and spectroscopic methods for characterizing oligomer folding, and describe extensive results obtained for diverse proteins, ranging from dimers to octamers and higher order aggregates. To our knowledge, this area has not been reviewed comprehensively in years, and the collective progress is impressive. The results provide evolutionary insights into the development of subunit interfaces, mechanisms of oligomer folding, and contributions of oligomerization to protein stability, function and regulation. Thermodynamic analyses have also proven valuable for understanding protein misfolding and aggregation mechanisms, suggesting new therapeutic avenues. Successful recent designs of novel, functional proteins demonstrate increased understanding of oligomer folding. Further rigorous analyses using multiple experimental and computational approaches are still required, however, to achieve consistent and accurate prediction of oligomer folding energetics. Modeling the energetics remains challenging but is a promising avenue for future advances.
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Affiliation(s)
- Colleen M Doyle
- Guelph-Waterloo Centre for Graduate Studies in Chemistry and Biochemistry, and Department of Chemistry, University of Waterloo, 200 University Ave. West, Waterloo, ON, Canada
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Blaber M, Lee J, Longo L. Emergence of symmetric protein architecture from a simple peptide motif: evolutionary models. Cell Mol Life Sci 2012; 69:3999-4006. [PMID: 22790181 PMCID: PMC11115074 DOI: 10.1007/s00018-012-1077-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2012] [Revised: 06/22/2012] [Accepted: 06/26/2012] [Indexed: 10/28/2022]
Abstract
Structural symmetry is observed in the majority of fundamental protein folds and gene duplication and fusion evolutionary processes are postulated to be responsible. However, convergent evolution leading to structural symmetry has also been proposed; additionally, there is debate regarding the extent to which exact primary structure symmetry is compatible with efficient protein folding. Issues of symmetry in protein evolution directly impact strategies for de novo protein design as symmetry can substantially simplify the design process. Additionally, when considering gene duplication and fusion in protein evolution, there are two competing models: "emergent architecture" and "conserved architecture". Recent experimental work has shed light on both the evolutionary process leading to symmetric protein folds as well as the ability of symmetric primary structure to efficiently fold. Such studies largely support a "conserved architecture" evolutionary model, suggesting that complex protein architecture was an early evolutionary achievement involving oligomerization of smaller polypeptides.
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Affiliation(s)
- Michael Blaber
- Department of Biomedical Sciences, College of Medicine, Florida State University, 1115 West Call St., Tallahassee, FL, 32306-4300, USA,
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Broom A, Doxey AC, Lobsanov YD, Berthin LG, Rose DR, Howell PL, McConkey BJ, Meiering EM. Modular evolution and the origins of symmetry: reconstruction of a three-fold symmetric globular protein. Structure 2011; 20:161-71. [PMID: 22178248 DOI: 10.1016/j.str.2011.10.021] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Revised: 10/09/2011] [Accepted: 10/24/2011] [Indexed: 10/14/2022]
Abstract
The high frequency of internal structural symmetry in common protein folds is presumed to reflect their evolutionary origins from the repetition and fusion of ancient peptide modules, but little is known about the primary sequence and physical determinants of this process. Unexpectedly, a sequence and structural analysis of symmetric subdomain modules within an abundant and ancient globular fold, the β-trefoil, reveals that modular evolution is not simply a relic of the ancient past, but is an ongoing and recurring mechanism for regenerating symmetry, having occurred independently in numerous existing β-trefoil proteins. We performed a computational reconstruction of a β-trefoil subdomain module and repeated it to form a newly three-fold symmetric globular protein, ThreeFoil. In addition to its near perfect structural identity between symmetric modules, ThreeFoil is highly soluble, performs multivalent carbohydrate binding, and has remarkably high thermal stability. These findings have far-reaching implications for understanding the evolution and design of proteins via subdomain modules.
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Affiliation(s)
- Aron Broom
- Guelph-Waterloo Centre for Graduate Studies in Chemistry and Biochemistry, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1, Canada
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12
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Experimental support for the evolution of symmetric protein architecture from a simple peptide motif. Proc Natl Acad Sci U S A 2010; 108:126-30. [PMID: 21173271 DOI: 10.1073/pnas.1015032108] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The majority of protein architectures exhibit elements of structural symmetry, and "gene duplication and fusion" is the evolutionary mechanism generally hypothesized to be responsible for their emergence from simple peptide motifs. Despite the central importance of the gene duplication and fusion hypothesis, experimental support for a plausible evolutionary pathway for a specific protein architecture has yet to be effectively demonstrated. To address this question, a unique "top-down symmetric deconstruction" strategy was utilized to successfully identify a simple peptide motif capable of recapitulating, via gene duplication and fusion processes, a symmetric protein architecture (the threefold symmetric β-trefoil fold). The folding properties of intermediary forms in this deconstruction agree precisely with a previously proposed "conserved architecture" model for symmetric protein evolution. Furthermore, a route through foldable sequence-space between the simple peptide motif and extant protein fold is demonstrated. These results provide compelling experimental support for a plausible evolutionary pathway of symmetric protein architecture via gene duplication and fusion processes.
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