51
views
0
recommends
+1 Recommend
0 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: found
      Is Open Access

      Otoferlin is a calcium sensor that directly regulates SNARE-mediated membrane fusion

      research-article
      1 , 2 , 1 , 2 ,
      The Journal of Cell Biology
      The Rockefeller University Press

      Read this article at

      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          Mutations in otoferlin are linked to human hearing loss. New research defines a function for this C2 domain–containing protein in synaptic vesicle exocytosis in cochlear hair cells.

          Abstract

          Otoferlin is a large multi–C2 domain protein proposed to act as a calcium sensor that regulates synaptic vesicle exocytosis in cochlear hair cells. Although mutations in otoferlin have been associated with deafness, its contribution to neurotransmitter release is unresolved. Using recombinant proteins, we demonstrate that five of the six C2 domains of otoferlin sense calcium with apparent dissociation constants that ranged from 13–25 µM; in the presence of membranes, these apparent affinities increase by up to sevenfold. Using a reconstituted membrane fusion assay, we found that five of the six C2 domains of otoferlin stimulate membrane fusion in a calcium-dependent manner. We also demonstrate that a calcium binding–deficient form of the C2C domain is incapable of stimulating membrane fusion, further underscoring the importance of calcium for the protein’s function. These results demonstrate for the first time that otoferlin is a calcium sensor that can directly regulate soluble N-ethyl-maleimide sensitive fusion protein attachment protein receptor–mediated membrane fusion reactions.

          Related collections

          Most cited references28

          • Record: found
          • Abstract: found
          • Article: not found

          Mechanisms of tryptophan fluorescence shifts in proteins.

          Tryptophan fluorescence wavelength is widely used as a tool to monitor changes in proteins and to make inferences regarding local structure and dynamics. We have predicted the fluorescence wavelengths of 19 tryptophans in 16 proteins, starting with crystal structures and using a hybrid quantum mechanical-classical molecular dynamics method with the assumption that only electrostatic interactions of the tryptophan ring electron density with the surrounding protein and solvent affect the transition energy. With only one adjustable parameter, the scaling of the quantum mechanical atomic charges as seen by the protein/solvent environment, the mean absolute deviation between predicted and observed fluorescence maximum wavelength is 6 nm. The modeling of electrostatic interactions, including hydration, in proteins is vital to understanding function and structure, and this study helps to assess the effectiveness of current electrostatic models.
            Bookmark
            • Record: found
            • Abstract: found
            • Article: not found

            How does synaptotagmin trigger neurotransmitter release?

            Neurotransmitter release at synapses involves a highly specialized form of membrane fusion that is triggered by Ca(2+) ions and is optimized for speed. These observations were established decades ago, but only recently have the molecular mechanisms that underlie this process begun to come into view. Here, we summarize findings obtained from genetically modified neurons and neuroendocrine cells, as well as from reconstituted systems, which are beginning to reveal the molecular mechanism by which Ca(2+)-acting on the synaptic vesicle (SV) protein synaptotagmin I (syt)-triggers rapid exocytosis. This work sheds light not only on presynaptic aspects of synaptic transmission, but also on the fundamental problem of membrane fusion, which has remained a puzzle that has yet to be solved in any biological system.
              Bookmark
              • Record: found
              • Abstract: found
              • Article: not found

              Transmitter release at the hair cell ribbon synapse.

              Neurotransmitters are released continuously at ribbon synapses in the retina and cochlea. Notably, a single ribbon synapse of inner hair cells provides the entire input to each cochlear afferent fiber. We investigated hair cell transmitter release in the postnatal rat cochlea by recording excitatory postsynaptic currents (EPSCs) from afferent boutons directly abutting the ribbon synapse. EPSCs were carried by rapidly gating AMPA receptors. EPSCs were clustered in time, indicating the possibility of coordinate release. Amplitude distributions of spontaneous EPSCs were highly skewed, peaking at 0.4 nS and ranging up to 20 times larger. Hair cell depolarization increased EPSC frequency up to 150 Hz without altering the amplitude distribution. We propose that the ribbon synapse operates by multivesicular release, possibly to achieve high-frequency transmission.
                Bookmark

                Author and article information

                Journal
                J Cell Biol
                J. Cell Biol
                jcb
                The Journal of Cell Biology
                The Rockefeller University Press
                0021-9525
                1540-8140
                4 October 2010
                : 191
                : 1
                : 187-197
                Affiliations
                [1 ]Howard Hughes Medical Institute and [2 ]Department of Physiology, University of Wisconsin, Madison, WI 53706
                Author notes
                Correspondence to Edwin R. Chapman: chapman@ 123456physiology.wisc.edu
                Article
                201002089
                10.1083/jcb.201002089
                2953437
                20921140
                21b064f2-412a-42ef-bc86-7e2a5ade4ecb
                © 2010 Johnson and Chapman

                This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

                History
                : 16 February 2010
                : 7 September 2010
                Categories
                Research Articles
                Article

                Cell biology
                Cell biology

                Comments

                Comment on this article