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Tseng YH, Ma TL, Tan DH, Su AJA, Washington KM, Wang CC, Huang YC, Wu MC, Su WF. Injectable Hydrogel Guides Neurons Growth with Specific Directionality. Int J Mol Sci 2023; 24:ijms24097952. [PMID: 37175657 PMCID: PMC10178216 DOI: 10.3390/ijms24097952] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2023] [Revised: 04/19/2023] [Accepted: 04/25/2023] [Indexed: 05/15/2023] Open
Abstract
Visual disabilities affect more than 250 million people, with 43 million suffering from irreversible blindness. The eyes are an extension of the central nervous system which cannot regenerate. Neural tissue engineering is a potential method to cure the disease. Injectability is a desirable property for tissue engineering scaffolds which can eliminate some surgical procedures and reduce possible complications and health risks. We report the development of the anisotropic structured hydrogel scaffold created by a co-injection of cellulose nanofiber (CNF) solution and co-polypeptide solution. The positively charged poly (L-lysine)-r-poly(L-glutamic acid) with 20 mol% of glutamic acid (PLLGA) is crosslinked with negatively charged CNF while promoting cellular activity from the acid nerve stimulate. We found that CNF easily aligns under shear forces from injection and is able to form hydrogel with an ordered structure. Hydrogel is mechanically strong and able to support, guide, and stimulate neurite growth. The anisotropy of our hydrogel was quantitatively determined in situ by 2D optical microscopy and 3D X-ray tomography. The effects of PLLGA:CNF blend ratios on cell viability, neurite growth, and neuronal signaling are systematically investigated in this study. We determined the optimal blend composition for stimulating directional neurite growth yielded a 16% increase in length compared with control, reaching anisotropy of 30.30% at 10°/57.58% at 30°. Using measurements of calcium signaling in vitro, we found a 2.45-fold increase vs. control. Based on our results, we conclude this novel material and unique injection method has a high potential for application in neural tissue engineering.
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Affiliation(s)
- Yun-Hsiu Tseng
- Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Tien-Li Ma
- Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Dun-Heng Tan
- Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - An-Jey A Su
- Department of Surgery, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Kia M Washington
- Department of Surgery, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Chun-Chieh Wang
- National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Yu-Ching Huang
- Department of Materials Engineering, Ming Chi University of Technology, New Taipei 24301, Taiwan
| | - Ming-Chung Wu
- Department of Chemical and Materials Engineering, Chang Gung University, Taoyuan 33302, Taiwan
- Center for Green Technology, Chang Gung University, Taoyuan 33302, Taiwan
- Division of Neonatology, Department of Pediatrics, Chang Gung Memorial Hospital at Linkou, Taoyuan 33305, Taiwan
| | - Wei-Fang Su
- Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
- Department of Materials Engineering, Ming Chi University of Technology, New Taipei 24301, Taiwan
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Puljung MC. Cryo-electron microscopy structures and progress toward a dynamic understanding of K ATP channels. J Gen Physiol 2018; 150:653-669. [PMID: 29685928 PMCID: PMC5940251 DOI: 10.1085/jgp.201711978] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Accepted: 03/26/2018] [Indexed: 12/11/2022] Open
Abstract
Puljung reviews recent cryo-EM KATP channel structures and proposes a mechanism by which ligand binding results in channel opening. Adenosine triphosphate (ATP)–sensitive K+ (KATP) channels are molecular sensors of cell metabolism. These hetero-octameric channels, comprising four inward rectifier K+ channel subunits (Kir6.1 or Kir6.2) and four sulfonylurea receptor (SUR1 or SUR2A/B) subunits, detect metabolic changes via three classes of intracellular adenine nucleotide (ATP/ADP) binding site. One site, located on the Kir subunit, causes inhibition of the channel when ATP or ADP is bound. The other two sites, located on the SUR subunit, excite the channel when bound to Mg nucleotides. In pancreatic β cells, an increase in extracellular glucose causes a change in oxidative metabolism and thus turnover of adenine nucleotides in the cytoplasm. This leads to the closure of KATP channels, which depolarizes the plasma membrane and permits Ca2+ influx and insulin secretion. Many of the molecular details regarding the assembly of the KATP complex, and how changes in nucleotide concentrations affect gating, have recently been uncovered by several single-particle cryo-electron microscopy structures of the pancreatic KATP channel (Kir6.2/SUR1) at near-atomic resolution. Here, the author discusses the detailed picture of excitatory and inhibitory ligand binding to KATP that these structures present and suggests a possible mechanism by which channel activation may proceed from the ligand-binding domains of SUR to the channel pore.
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Affiliation(s)
- Michael C Puljung
- Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford, England, UK
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Martin GM, Kandasamy B, DiMaio F, Yoshioka C, Shyng SL. Anti-diabetic drug binding site in a mammalian K ATP channel revealed by Cryo-EM. eLife 2017; 6:31054. [PMID: 29035201 PMCID: PMC5655142 DOI: 10.7554/elife.31054] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2017] [Accepted: 10/11/2017] [Indexed: 12/25/2022] Open
Abstract
Sulfonylureas are anti-diabetic medications that act by inhibiting pancreatic KATP channels composed of SUR1 and Kir6.2. The mechanism by which these drugs interact with and inhibit the channel has been extensively investigated, yet it remains unclear where the drug binding pocket resides. Here, we present a cryo-EM structure of a hamster SUR1/rat Kir6.2 channel bound to a high-affinity sulfonylurea drug glibenclamide and ATP at 3.63 Å resolution, which reveals unprecedented details of the ATP and glibenclamide binding sites. Importantly, the structure shows for the first time that glibenclamide is lodged in the transmembrane bundle of the SUR1-ABC core connected to the first nucleotide binding domain near the inner leaflet of the lipid bilayer. Mutation of residues predicted to interact with glibenclamide in our model led to reduced sensitivity to glibenclamide. Our structure provides novel mechanistic insights of how sulfonylureas and ATP interact with the KATP channel complex to inhibit channel activity.
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Affiliation(s)
- Gregory M Martin
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, United States
| | - Balamurugan Kandasamy
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, United States
| | - Frank DiMaio
- Department of Biochemistry, University of Washington, Seattle, United States
| | - Craig Yoshioka
- Department of Biomedical Engineering, Oregon Health and Science University, Portland, United States
| | - Show-Ling Shyng
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, United States
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Moran O, Grottesi A, Chadburn AJ, Tammaro P. Parametrisation of the free energy of ATP binding to wild-type and mutant Kir6.2 potassium channels. Biophys Chem 2012; 171:76-83. [PMID: 23219002 DOI: 10.1016/j.bpc.2012.10.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2012] [Revised: 10/30/2012] [Accepted: 10/30/2012] [Indexed: 11/28/2022]
Abstract
ATP-sensitive K(+) (K(ATP)) channels, comprised of pore-forming Kir6.x and regulatory SURx subunits, play important roles in many cellular functions; because of their sensitivity to inhibition by intracellular ATP, K(ATP) channels provide a link between cell metabolism and membrane electrical activity. We constructed structural homology models of Kir6.2 and a series of Kir6.2 channels carrying mutations within the putative ATP-binding site. Computational docking was carried out to determine the conformation of ATP in its binding site. The Linear Interaction Energy (LIE) method was used to estimate the free-energy of ATP binding to wild-type and mutant Kir6.2 channels. Comparisons of the theoretical binding free energies for ATP with those determined from mutational experiments enabled the identification of the most probable conformation of ATP bound to the Kir6.2 channel. A set of LIE parameters was defined that may enable prediction of the effects of additional Kir6.2 mutations within the ATP binding site on the affinity for ATP.
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Diaz-Sylvester PL, Copello JA. Voltage-dependent modulation of cardiac ryanodine receptors (RyR2) by protamine. PLoS One 2009; 4:e8315. [PMID: 20016815 PMCID: PMC2789381 DOI: 10.1371/journal.pone.0008315] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Accepted: 11/19/2009] [Indexed: 11/18/2022] Open
Abstract
It has been reported that protamine (>10 µg/ml) blocks single skeletal RyR1 channels and inhibits RyR1-mediated Ca2+ release from sarcoplasmic reticulum microsomes. We extended these studies to cardiac RyR2 reconstituted into planar lipid bilayers. We found that protamine (0.02–20 µg/ml) added to the cytosolic surface of fully activated RyR2 affected channel activity in a voltage-dependent manner. At membrane voltage (Vm; SR lumen - cytosol) = 0 mV, protamine induced conductance transitions to several intermediate states (substates) as well as full block of RyR2. At Vm>10 mV, the substate with the highest level of conductance was predominant. Increasing Vm from 0 to +80 mV, decreased the number of transitions and residence of the channel in this substate. The drop in current amplitude (full opening to substate) had the same magnitude at 0 and +80 mV despite the ∼3-fold increase in amplitude of the full opening. This is more similar to rectification of channel conductance induced by other polycations than to the action of selective conductance modifiers (ryanoids, imperatoxin). A distinctive effect of protamine (which might be shared with polylysines and histones but not with non-peptidic polycations) is the activation of RyR2 in the presence of nanomolar cytosolic Ca2+ and millimolar Mg2+ levels. Our results suggest that RyRs would be subject to dual modulation (activation and block) by polycationic domains of neighboring proteins via electrostatic interactions. Understanding these interactions could be important as such anomalies may be associated with the increased RyR2-mediated Ca2+ leak observed in cardiac diseases.
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Affiliation(s)
- Paula L. Diaz-Sylvester
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois, United States of America
| | - Julio A. Copello
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois, United States of America
- * E-mail:
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Tammaro P, Ashcroft FM. A mutation in the ATP-binding site of the Kir6.2 subunit of the KATP channel alters coupling with the SUR2A subunit. J Physiol 2007; 584:743-53. [PMID: 17855752 PMCID: PMC2277002 DOI: 10.1113/jphysiol.2007.143149] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Mutations in the pore-forming subunit of the ATP-sensitive K(+) (K(ATP)) channel Kir6.2 cause neonatal diabetes. Understanding the molecular mechanism of action of these mutations has provided valuable insight into the relationship between the structure and function of the K(ATP) channel. When Kir6.2 containing a mutation (F333I) in the putative ATP-binding site is coexpressed with the cardiac type of regulatory K(ATP) channel subunit, SUR2A, the channel sensitivity to ATP inhibition is reduced and the intrinsic open probability (P(o)) is increased. However, the extent of macroscopic current activation by MgADP was unaffected. Here we examine rundown and MgADP activation of wild-type and Kir6.2-F333I/SUR2A channels using single-channel recording, noise analysis and spectral analysis. We also compare the effect of mutating the adjacent residue, G334, on rundown and MgADP activation. All three approaches indicated that rundown of Kir6.2-F333I/SUR2A channels is due to a reduction in the number of active channels in the patch and that MgADP reactivation involves recruitment of inactive channels. In contrast, rundown and MgADP reactivation of wild-type and Kir6.2-G334D/SUR2A channels, and of Kir6.2-F333I/SUR1 channels, involve a gradual change in P(o). Our results suggest that F333 in Kir6.2 interacts functionally with SUR2A to modulate channel rundown and MgADP activation. This interaction is fairly specific as it is not disturbed when the adjacent residue (G334) is mutated. It is also not a consequence of the enhanced P(o) of Kir6.2-F333I/SUR2A channels, as it is not found for other mutant channels with high P(o) (Kir6.2-I296L/SUR2A).
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Affiliation(s)
- Paolo Tammaro
- Department of Physiology, Anatomy and Genetics, Oxford University, Oxford, UK
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Masia R, Koster JC, Tumini S, Chiarelli F, Colombo C, Nichols CG, Barbetti F. An ATP-binding mutation (G334D) in KCNJ11 is associated with a sulfonylurea-insensitive form of developmental delay, epilepsy, and neonatal diabetes. Diabetes 2007; 56:328-36. [PMID: 17259376 DOI: 10.2337/db06-1275] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Mutations in the pancreatic ATP-sensitive K(+) channel (K(ATP) channel) cause permanent neonatal diabetes mellitus (PNDM) in humans. All of the K(ATP) channel mutations examined result in decreased ATP inhibition, which in turn is predicted to suppress insulin secretion. Here we describe a patient with severe PNDM, which includes developmental delay and epilepsy, in addition to neonatal diabetes (developmental delay, epilepsy, and neonatal diabetes [DEND]), due to a G334D mutation in the Kir6.2 subunit of K(ATP) channel. The patient was wholly unresponsive to sulfonylurea therapy (up to 1.14 mg . kg(-1) . day(-1)) and remained insulin dependent. Consistent with the putative role of G334 as an ATP-binding residue, reconstituted homomeric and mixed WT+G334D channels exhibit absent or reduced ATP sensitivity but normal gating behavior in the absence of ATP. In disagreement with the sulfonylurea insensitivity of the affected patient, the G334D mutation has no effect on the sulfonylurea inhibition of reconstituted channels in excised patches. However, in macroscopic rubidium-efflux assays in intact cells, reconstituted mutant channels do exhibit a decreased, but still present, sulfonylurea response. The results demonstrate that ATP-binding site mutations can indeed cause DEND and suggest the possibility that sulfonylurea insensitivity of such patients may be a secondary reflection of the presence of DEND rather than a simple reflection of the underlying molecular basis.
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Affiliation(s)
- Ricard Masia
- Department of Cell Biology and Physiology, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA
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Hetényi C, van der Spoel D. Blind docking of drug-sized compounds to proteins with up to a thousand residues. FEBS Lett 2006; 580:1447-50. [PMID: 16460734 DOI: 10.1016/j.febslet.2006.01.074] [Citation(s) in RCA: 219] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2005] [Revised: 12/20/2005] [Accepted: 01/24/2006] [Indexed: 10/25/2022]
Abstract
Blind docking was introduced for the detection of possible binding sites and modes of peptide ligands by scanning the entire surface of protein targets. In the present study, the method is tested on a group of drug-sized compounds and proteins with up to a thousand amino acid residues. Both proteins from complex structures and ligand-free proteins were used as targets. Robustness, limitations and future perspectives of the method are discussed. It is concluded that blind docking can be used for unbiased mapping of the binding patterns of drug candidates.
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Affiliation(s)
- Csaba Hetényi
- Department of Biochemistry, Eötvös Loránd University, 1/C Pázmány P. sétány, 1117 Budapest, Hungary.
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