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McSpadden ED, Xia Z, Chi CC, Susa AC, Shah NH, Gee CL, Williams ER, Kuriyan J. Variation in assembly stoichiometry in non-metazoan homologs of the hub domain of Ca 2+ /calmodulin-dependent protein kinase II. Protein Sci 2019; 28:1071-1082. [PMID: 30942928 DOI: 10.1002/pro.3614] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Accepted: 04/01/2019] [Indexed: 11/12/2022]
Abstract
The multi-subunit Ca2+ /calmodulin-dependent protein kinase II (CaMKII) holoenzyme plays a critical role in animal learning and memory. The kinase domain of CaMKII is connected by a flexible linker to a C-terminal hub domain that assembles into a 12- or 14-subunit scaffold that displays the kinase domains around it. Studies on CaMKII suggest that the stoichiometry and dynamic assembly/disassembly of hub oligomers may be important for CaMKII regulation. Although CaMKII is a metazoan protein, genes encoding predicted CaMKII-like hub domains, without associated kinase domains, are found in the genomes of some green plants and bacteria. We show that the hub domains encoded by three related green algae, Chlamydomonas reinhardtii, Volvox carteri f. nagarensis, and Gonium pectoral, assemble into 16-, 18-, and 20-subunit oligomers, as assayed by native protein mass spectrometry. These are the largest known CaMKII hub domain assemblies. A crystal structure of the hub domain from C. reinhardtii reveals an 18-subunit organization. We identified four intra-subunit hydrogen bonds in the core of the fold that are present in the Chlamydomonas hub domain, but not in metazoan hubs. When six point mutations designed to recapitulate these hydrogen bonds were introduced into the human CaMKII-α hub domain, the mutant protein formed assemblies with 14 and 16 subunits, instead of the normal 12- and 14-subunit assemblies. Our results show that the stoichiometric balance of CaMKII hub assemblies can be shifted readily by small changes in sequence.
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Affiliation(s)
- Ethan D McSpadden
- Department of Molecular and Cell Biology, University of California, Berkeley, California.,California Institute for Quantitative Biosciences (QB3), University of California, Berkeley, California.,Howard Hughes Medical Institute, University of California, Berkeley, California
| | - Zijie Xia
- Department of Chemistry, University of California, Berkeley, California
| | - Chris C Chi
- Department of Molecular and Cell Biology, University of California, Berkeley, California.,California Institute for Quantitative Biosciences (QB3), University of California, Berkeley, California.,Howard Hughes Medical Institute, University of California, Berkeley, California
| | - Anna C Susa
- Department of Chemistry, University of California, Berkeley, California
| | - Neel H Shah
- Department of Molecular and Cell Biology, University of California, Berkeley, California.,California Institute for Quantitative Biosciences (QB3), University of California, Berkeley, California.,Howard Hughes Medical Institute, University of California, Berkeley, California
| | - Christine L Gee
- Department of Molecular and Cell Biology, University of California, Berkeley, California.,California Institute for Quantitative Biosciences (QB3), University of California, Berkeley, California.,Howard Hughes Medical Institute, University of California, Berkeley, California
| | - Evan R Williams
- California Institute for Quantitative Biosciences (QB3), University of California, Berkeley, California.,Department of Chemistry, University of California, Berkeley, California
| | - John Kuriyan
- Department of Molecular and Cell Biology, University of California, Berkeley, California.,California Institute for Quantitative Biosciences (QB3), University of California, Berkeley, California.,Howard Hughes Medical Institute, University of California, Berkeley, California.,Department of Chemistry, University of California, Berkeley, California.,Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California
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2
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Susa AC, Lippens JL, Xia Z, Loo JA, Campuzano IDG, Williams ER. Submicrometer Emitter ESI Tips for Native Mass Spectrometry of Membrane Proteins in Ionic and Nonionic Detergents. J Am Soc Mass Spectrom 2018; 29:203-206. [PMID: 29027132 PMCID: PMC5786471 DOI: 10.1007/s13361-017-1793-x] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Revised: 08/21/2017] [Accepted: 08/23/2017] [Indexed: 05/11/2023]
Abstract
Native mass spectrometry (native-MS) of membrane proteins typically requires a detergent screening protocol, protein solubilization in the preferred detergent, followed by protein liberation from the micelle by collisional activation. Here, submicrometer nano-ESI emitter tips are used for native-MS of membrane proteins solubilized in both nonionic and ionic detergent solutions. With the submicrometer nano-ESI emitter tips, resolved charge-state distributions of membrane protein ions are obtained from a 150 mM NaCl, 25 mM Tris-HCl with 1.1% octyl glucoside solution. The relative abundances of NaCl and detergent cluster ions at high m /z are significantly reduced with the submicrometer emitters compared with larger nano-ESI emitters that are commonly used. This technique is beneficial for significantly decreasing the abundances (by two to three orders of magnitude compared with the larger tip size: 1.6 μm) of detergent cluster ions formed from aqueous ammonium acetate solutions containing detergents that can overlap with the membrane protein ion signal. Resolved charge-state distributions of membrane protein ions from aqueous ammonium acetate solutions containing ionic detergents were obtained with the submicrometer nano-ESI emitters; this is the first report of native-MS of membrane proteins solubilized by ionic detergents. Graphical Abstract.
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Affiliation(s)
- Anna C Susa
- Department of Chemistry, University of California, Berkeley, CA, 94720-1460, USA
| | | | - Zijie Xia
- Department of Chemistry, University of California, Berkeley, CA, 94720-1460, USA
| | - Joseph A Loo
- Department of Chemistry and Biochemistry, and Department of Biological Chemistry, University of California-Los Angeles, Los Angeles, CA, 90095, USA
| | | | - Evan R Williams
- Department of Chemistry, University of California, Berkeley, CA, 94720-1460, USA.
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3
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Mortensen DN, Susa AC, Williams ER. Collisional Cross-Sections with T-Wave Ion Mobility Spectrometry without Experimental Calibration. J Am Soc Mass Spectrom 2017; 28:1282-1292. [PMID: 28432656 DOI: 10.1007/s13361-017-1669-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Revised: 03/21/2017] [Accepted: 03/27/2017] [Indexed: 06/07/2023]
Abstract
A method for relating traveling-wave ion mobility spectrometry (TWIMS) drift times with collisional cross-sections using computational simulations is presented. This method is developed using SIMION modeling of the TWIMS potential wave and equations that describe the velocity of ions in gases induced by electric fields. The accuracy of this method is assessed by comparing the collisional cross-sections of 70 different reference ions obtained using this method with those obtained from static drift tube ion mobility measurements. The cross-sections obtained here with low wave velocities are very similar to those obtained using static drift (average difference = 0.3%) for ions formed from both denaturing and buffered aqueous solutions. In contrast, the cross-sections obtained with high wave velocities are significantly greater, especially for ions formed from buffered aqueous solutions. These higher cross-sections at high wave velocities may result from high-order factors not accounted for in the model presented here or from the protein ions unfolding during TWIMS. Results from this study demonstrate that collisional cross-sections can be obtained from single TWIMS drift time measurements, but that low wave velocities and gentle instrument conditions should be used in order to minimize any uncertainties resulting from high-order effects not accounted for in the present model and from any protein unfolding that might occur. Thus, the method presented here eliminates the need to calibrate TWIMS drift times with collisional cross-sections measured using other ion mobility devices. Graphical Abstract ᅟ.
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Affiliation(s)
- Daniel N Mortensen
- Department of Chemistry, University of California, Berkeley, CA, 94720-1460, USA
| | - Anna C Susa
- Department of Chemistry, University of California, Berkeley, CA, 94720-1460, USA
| | - Evan R Williams
- Department of Chemistry, University of California, Berkeley, CA, 94720-1460, USA.
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4
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Elliott AG, Harper CC, Lin HW, Susa AC, Xia Z, Williams ER. Simultaneous Measurements of Mass and Collisional Cross-Section of Single Ions with Charge Detection Mass Spectrometry. Anal Chem 2017. [PMID: 28621517 DOI: 10.1021/acs.analchem.7b01675] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The masses and mobilities of single multiply charged ions of cytochrome c, ubiquitin, myoglobin, and bovine serum albumin formed by electrospray ionization are measured using charge detection mass spectrometry (CDMS). Single ions are trapped and repeatedly measured as they oscillate inside an electrostatic ion trap with cone electrodes for up to the maximum trapping time set at 500 ms. The histograms of the many single ion oscillation frequencies have resolved peaks that correspond to the different charge states of each protein. The m/z of each ion is determined from the initial oscillation frequency histogram, and the evolution of the ion energy with time is obtained from the changing frequency. A short-time Fourier transform of the time-domain data indicates that the increase in ion frequency occurs gradually with time with occasional sudden jumps in frequency. The frequency jumps are similar for each protein and may be caused by collision-induced changes in the ion trajectory. The rate of the gradual frequency shift increases with protein mass and charge state. This gradual frequency change is due to ion energy loss from collisions with the background gas. The total energy lost by an ion is determined from the latter frequency shifts normalized to a 500 ms lifetime, and these values increase nearly linearly with measured collisional cross-sections for these protein ions. These results show that the mass and collisional cross-section of single multiply charged ions can be obtained from these CDMS measurements by using proteins with known collisional cross-sections for calibration.
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Affiliation(s)
- Andrew G Elliott
- Department of Chemistry, University of California , Berkeley, California 94720-1460, United States
| | - Conner C Harper
- Department of Chemistry, University of California , Berkeley, California 94720-1460, United States
| | - Haw-Wei Lin
- Department of Chemistry, University of California , Berkeley, California 94720-1460, United States
| | - Anna C Susa
- Department of Chemistry, University of California , Berkeley, California 94720-1460, United States
| | - Zijie Xia
- Department of Chemistry, University of California , Berkeley, California 94720-1460, United States
| | - Evan R Williams
- Department of Chemistry, University of California , Berkeley, California 94720-1460, United States
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5
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Affiliation(s)
- Anna C. Susa
- Department of Chemistry; University of California, Berkeley, California; B42 Hildebrand Hall Berkeley CA 94720 USA
| | - Zijie Xia
- Department of Chemistry; University of California, Berkeley, California; B42 Hildebrand Hall Berkeley CA 94720 USA
| | - Evan R. Williams
- Department of Chemistry; University of California, Berkeley, California; B42 Hildebrand Hall Berkeley CA 94720 USA
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6
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Susa AC, Xia Z, Williams ER. Native Mass Spectrometry from Common Buffers with Salts That Mimic the Extracellular Environment. Angew Chem Int Ed Engl 2017; 56:7912-7915. [DOI: 10.1002/anie.201702330] [Citation(s) in RCA: 63] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2017] [Indexed: 12/18/2022]
Affiliation(s)
- Anna C. Susa
- Department of Chemistry; University of California, Berkeley, California; B42 Hildebrand Hall Berkeley CA 94720 USA
| | - Zijie Xia
- Department of Chemistry; University of California, Berkeley, California; B42 Hildebrand Hall Berkeley CA 94720 USA
| | - Evan R. Williams
- Department of Chemistry; University of California, Berkeley, California; B42 Hildebrand Hall Berkeley CA 94720 USA
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7
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Susa AC, Xia Z, Williams ER. Small Emitter Tips for Native Mass Spectrometry of Proteins and Protein Complexes from Nonvolatile Buffers That Mimic the Intracellular Environment. Anal Chem 2017; 89:3116-3122. [DOI: 10.1021/acs.analchem.6b04897] [Citation(s) in RCA: 97] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Anna C. Susa
- Department of Chemistry, University of California, Berkeley, California 94720-1460, United States
| | - Zijie Xia
- Department of Chemistry, University of California, Berkeley, California 94720-1460, United States
| | - Evan R. Williams
- Department of Chemistry, University of California, Berkeley, California 94720-1460, United States
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8
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Susa AC, Xia Z, Tang HYH, Tainer JA, Williams ER. Charging of Proteins in Native Mass Spectrometry. J Am Soc Mass Spectrom 2017; 28:332-340. [PMID: 27734326 PMCID: PMC5283922 DOI: 10.1007/s13361-016-1517-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Revised: 09/22/2016] [Accepted: 09/27/2016] [Indexed: 05/19/2023]
Abstract
Factors that influence the charging of protein ions formed by electrospray ionization from aqueous solutions in which proteins have native structures and function were investigated. Protein ions ranging in molecular weight from 12.3 to 79.7 kDa and pI values from 5.4 to 9.6 were formed from different solutions and reacted with volatile bases of gas-phase basicities higher than that of ammonia in the cell of a Fourier-transform ion cyclotron resonance mass spectrometer. The charge-state distribution of cytochrome c ions formed from aqueous ammonium or potassium acetate is the same. Moreover, ions formed from these two solutions do not undergo proton transfer to 2-fluoropyridine, which is 8 kcal/mol more basic than ammonia. These results provide compelling evidence that proton transfer between ammonia and protein ions does not limit protein ion charge in native electrospray ionization. Both circular dichroism and ion mobility measurements indicate that there are differences in conformations of proteins in pure water and aqueous ammonium acetate, and these differences can account for the difference in the extent of charging and proton-transfer reactivities of protein ions formed from these solutions. The extent of proton transfer of the protein ions with higher gas-phase basicity bases trends with how closely the protein ions are charged to the value predicted by the Rayleigh limit for spherical water droplets approximately the same size as the proteins. These results indicate that droplet charge limits protein ion charge in native mass spectrometry and are consistent with these ions being formed by the charged residue mechanism. Graphical Abstract ᅟ.
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Affiliation(s)
- Anna C Susa
- Department of Chemistry, University of California, Berkeley, CA, 94720-1460, USA
| | - Zijie Xia
- Department of Chemistry, University of California, Berkeley, CA, 94720-1460, USA
| | - Henry Y H Tang
- Department of Chemistry, University of California, Berkeley, CA, 94720-1460, USA
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - John A Tainer
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
- Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, 77030, USA
| | - Evan R Williams
- Department of Chemistry, University of California, Berkeley, CA, 94720-1460, USA.
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9
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Bhattacharyya M, Stratton MM, Going CC, McSpadden ED, Huang Y, Susa AC, Elleman A, Cao YM, Pappireddi N, Burkhardt P, Gee CL, Barros T, Schulman H, Williams ER, Kuriyan J. Molecular mechanism of activation-triggered subunit exchange in Ca(2+)/calmodulin-dependent protein kinase II. eLife 2016; 5. [PMID: 26949248 PMCID: PMC4859805 DOI: 10.7554/elife.13405] [Citation(s) in RCA: 72] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 03/03/2016] [Indexed: 12/04/2022] Open
Abstract
Activation triggers the exchange of subunits in Ca2+/calmodulin-dependent protein kinase II (CaMKII), an oligomeric enzyme that is critical for learning, memory, and cardiac function. The mechanism by which subunit exchange occurs remains elusive. We show that the human CaMKII holoenzyme exists in dodecameric and tetradecameric forms, and that the calmodulin (CaM)-binding element of CaMKII can bind to the hub of the holoenzyme and destabilize it to release dimers. The structures of CaMKII from two distantly diverged organisms suggest that the CaM-binding element of activated CaMKII acts as a wedge by docking at intersubunit interfaces in the hub. This converts the hub into a spiral form that can release or gain CaMKII dimers. Our data reveal a three-way competition for the CaM-binding element, whereby phosphorylation biases it towards the hub interface, away from the kinase domain and calmodulin, thus unlocking the ability of activated CaMKII holoenzymes to exchange dimers with unactivated ones. DOI:http://dx.doi.org/10.7554/eLife.13405.001 How does memory outlast the lifetime of the molecules that encode it? One enzyme that is found in neurons and has been suggested to help long-term memories to form is called CaMKII. Each CaMKII assembly is typically composed of 12 to 14 protein subunits associated in a ring and can exist in either an “unactivated” or “activated” state. In 2014, researchers showed that CaMKII assemblies can exchange subunits with each other. Importantly, an active CaMKII can mix with an unactivated CaMKII and share its activation state. CaMKII may use this mechanism to spread information to the next generation of proteins – thereby allowing activation to outlast the lifespan of the initially activated proteins. However the molecular mechanism that underlies this process was not clear. Now, Bhattacharyya et al. – including some of the researchers involved in the 2014 work – address two questions about this mechanism. How do subunits exchange between CaMKII assemblies? And how does the activation of CaMKII initiate subunit exchange? A closed-ring hub ties the subunits of CaMKII together, similar to the organization of the segments in an orange. To undergo subunit exchange, the hub must open up to release and accept subunits. Bhattacharyya et al. have now uncovered an intrinsic flexibility in the hub that is triggered by a short peptide segment in CaMKII. This segment, which is exposed in activated CaMKII but not in the unactivated form, can crack open the hub ring by binding between the hub subunits, like a finger separating the segments of an orange. This allows the hub to flex and expand, and once open, the hub’s flexibility allows room for subunits to be released or accepted. Although this subunit exchange mechanism could be a powerful means for spreading the activated state throughout signaling pathways, the biological relevance of this phenomenon has not been clarified. However, the mechanistic framework provided by Bhattacharyya et al. may allow new experiments to be performed that test the consequences of subunit exchange in live cells and organisms. It could also enable investigations into the importance of subunit exchange in long-term memory. DOI:http://dx.doi.org/10.7554/eLife.13405.002
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Affiliation(s)
- Moitrayee Bhattacharyya
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
| | - Margaret M Stratton
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
| | - Catherine C Going
- Department of Chemistry, University of California, Berkeley, Berkeley, United States
| | - Ethan D McSpadden
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
| | - Yongjian Huang
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States.,Biophysics Graduate Group, University of California, Berkeley, Berkeley, United States
| | - Anna C Susa
- Department of Chemistry, University of California, Berkeley, Berkeley, United States
| | - Anna Elleman
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
| | - Yumeng Melody Cao
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
| | - Nishant Pappireddi
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
| | - Pawel Burkhardt
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
| | - Christine L Gee
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
| | - Tiago Barros
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
| | | | - Evan R Williams
- Department of Chemistry, University of California, Berkeley, Berkeley, United States
| | - John Kuriyan
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States.,Biophysics Graduate Group, University of California, Berkeley, Berkeley, United States.,Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, United States
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10
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Susa AC, Wu C, Bernstein SL, Dupuis NF, Wang H, Raleigh DP, Shea JE, Bowers MT. Defining the molecular basis of amyloid inhibitors: human islet amyloid polypeptide-insulin interactions. J Am Chem Soc 2014; 136:12912-9. [PMID: 25144879 PMCID: PMC4183647 DOI: 10.1021/ja504031d] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2014] [Indexed: 11/28/2022]
Abstract
Human islet amyloid polypeptide (hIAPP or Amylin) is a 37 residue hormone that is cosecreted with insulin from the pancreatic islets. The aggregation of hIAPP plays a role in the progression of type 2 diabetes and contributes to the failure of islet cell grafts. Despite considerable effort, little is known about the mode of action of IAPP amyloid inhibitors, and this has limited rational drug design. Insulin is one of the most potent inhibitors of hIAPP fibril formation, but its inhibition mechanism is not understood. In this study, the aggregation of mixtures of hIAPP with insulin, as well as with the separate A and B chains of insulin, were characterized using ion mobility spectrometry-based mass spectrometry and atomic force microscopy. Insulin and the insulin B chain target the hIAPP monomer in its compact isoform and shift the equilibrium away from its extended isoform, an aggregation-prone conformation, and thus inhibit hIAPP from forming β-sheets and subsequently amyloid fibrils. All-atom molecular modeling supports these conclusions.
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Affiliation(s)
- Anna C. Susa
- Department
of Chemistry and Biochemistry, University
of California, Santa Barbara, California 93106, United States
| | - Chun Wu
- Department
of Chemistry and Biochemistry, University
of California, Santa Barbara, California 93106, United States
| | - Summer L. Bernstein
- Department
of Chemistry and Biochemistry, University
of California, Santa Barbara, California 93106, United States
| | - Nicholas F. Dupuis
- Department
of Chemistry and Biochemistry, University
of California, Santa Barbara, California 93106, United States
| | - Hui Wang
- Department
of Chemistry, Stony Brook University, Stony Brook, New York 11794-3400, United States
| | - Daniel P. Raleigh
- Department
of Chemistry, Stony Brook University, Stony Brook, New York 11794-3400, United States
| | - Joan-Emma Shea
- Department
of Chemistry and Biochemistry, University
of California, Santa Barbara, California 93106, United States
| | - Michael T. Bowers
- Department
of Chemistry and Biochemistry, University
of California, Santa Barbara, California 93106, United States
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11
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Susa AC, Mortensen DN, Williams ER. Effects of cations on protein and peptide charging in electrospray ionization from aqueous solutions. J Am Soc Mass Spectrom 2014; 25:918-27. [PMID: 24729190 PMCID: PMC4051497 DOI: 10.1007/s13361-014-0864-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/28/2013] [Revised: 02/12/2014] [Accepted: 02/18/2014] [Indexed: 05/11/2023]
Abstract
The effects of eight different cations with ionic radii between 69 and 337 pm on the charging of peptides and proteins with electrospray ionization from aqueous acetate salt solutions are reported. Significant adduction occurs for all cations except NH4(+), and the average protein charge is lower when formed from solutions containing salts compared with solutions without salts added. Circular dichroism and ion mobility results show the protein conformations are different in pure water compared with salt solutions, which likely affects the extent of charging. The average charge of protein and peptide ions formed from solutions with Li(+) and Cs(+), which have Gibbs solvation free energies (GSFEs) that differ by 225 kJ/mol, is similar. Lower charge states are typically formed from solutions with tetramethylammonium and tetraethylammonium that have lower GSFE values. Loss of the larger cations that have the lowest GSFEs is facile when adducted protein ions are collisionally activated, resulting in the formation of lower analyte charge states. This reaction pathway provides a route to produce abundant singly protonated protein ions under native mass spectrometry conditions. The average protein and peptide charge with NH4(+) is nearly the same as that with Rb(+) and K(+), cations with similar GSFE and ionic radii. This indicates that proton transfer from NH4(+) to proteins plays an insignificant role in the extent of protein charging in native mass spectrometry.
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Affiliation(s)
| | | | - Evan R. Williams
- Address correspondence to Prof. Evan R. Williams: Department of Chemistry, University of California, Berkeley, B42 Hildebrand Hall Berkeley, CA 94720, Phone: (510) 643-7161,
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12
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Cassou CA, Sterling HJ, Susa AC, Williams ER. Electrothermal supercharging in mass spectrometry and tandem mass spectrometry of native proteins. Anal Chem 2012. [PMID: 23194134 DOI: 10.1021/ac302256d] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Electrothermal supercharging of protein ions formed by electrospray ionization from buffered aqueous solutions results in significant increases to both the maximum and average charge states compared to native mass spectrometry in which ions are formed from the same solutions but with lower spray potentials. For eight of the nine proteins investigated, the maximum charge states of protonated ions formed from native solutions with electrothermal supercharging is greater than those obtained from conventional denaturing solutions consisting of water/methanol/acid, although the average charging is slightly lower owing to contributions of small populations of more folded low charge-state structures. Under these conditions, electrothermal supercharging is slightly less effective for anions than for cations. Equivalent sequence coverage (80%) is obtained with electron transfer dissociation of the same high charge-state ion of cytochrome c formed by electrothermal supercharging from native solutions and from denaturing solutions. Electrothermal supercharging should be advantageous for combining structural studies of proteins in native environments with mass spectrometers that have limited high m/z capabilities and for significantly improving tandem mass spectrometry performance for protein ions formed from solutions in which the molecules have native structures and activities.
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Affiliation(s)
- Catherine A Cassou
- Department of Chemistry, University of California, Berkeley, 94720-1460, United States
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13
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Abstract
The formation of high charge-state protein ions with nanoelectrospray ionization (nESI) from purely aqueous ammonium bicarbonate solutions at neutral pH, where the proteins have native or native-like conformations prior to ESI droplet formation, is demonstrated. This "electrothermal" supercharging method depends on the temperature of the instrument entrance capillary, the nESI spray potential, and the solution ionic strength and buffer, although other factors almost certainly contribute. Mass spectra obtained with electrothermal supercharging appear similar to those obtained from denaturing solutions where charging beyond the total number of basic sites can be achieved. For example, a 17+ ion of bovine ubiquitin was formed by nESI of a 100 mM ammonium bicarbonate, pH 7.0, solution, which is three more charges than the total number of basic amino acids plus the N-terminus. Heating of the ESI droplets in the vacuum/atmosphere interface and the concomitant denaturation of the protein in the ESI droplets prior to ion formation appears to be the primary origin of the very high charge-state ions formed from these purely aqueous, buffered solutions. nESI mass spectra resembling those obtained under traditional native or denaturing conditions can be reversibly obtained simply by toggling the spray voltage between low and high values.
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Affiliation(s)
- Harry J Sterling
- Department of Chemistry, University of California, Berkeley, California 94720-1460, United States
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