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Abstract
Over the last few decades, mass spectrometry-based proteomics has become an increasingly powerful tool that is now able to routinely detect and quantify thousands of proteins. A major advance for global protein quantification was the introduction of isobaric tags, which, in a single experiment, enabled the global quantification of proteins across multiple samples. Herein, these methods are referred to as multiplexed proteomics. The principles, advantages, and drawbacks of various multiplexed proteomics techniques are discussed and compared with alternative approaches. We also discuss how the emerging combination of multiplexing with targeted proteomics might enable the reliable and high-quality quantification of very low abundance proteins across multiple conditions. Lastly, we suggest that fusing multiplexed proteomics with data-independent acquisition approaches might enable the comparison of hundreds of different samples without missing values, while maintaining the superb measurement precision and accuracy obtainable with isobaric tag quantification.
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Affiliation(s)
- Nishant Pappireddi
- Department of Molecular Biology, Princeton University, Icahn Laboratory, #246, Washington Road, Princeton, NJ, 08544, USA.,The Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, 08544, USA
| | - Lance Martin
- Department of Molecular Biology, Princeton University, Icahn Laboratory, #246, Washington Road, Princeton, NJ, 08544, USA.,The Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, 08544, USA
| | - Martin Wühr
- Department of Molecular Biology, Princeton University, Icahn Laboratory, #246, Washington Road, Princeton, NJ, 08544, USA.,The Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, 08544, USA
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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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