Original Research ARTICLE
Functional status of neuronal calcium sensor-1 is modulated by zinc binding
- 1Aix-Marseille Université, France
- 2Institute of Physiologically Active Compounds (RAS), Russia
- 3Lomonosov Moscow State University, Russia
- 4Institute for Biological Instrumentation (RAS), Russia
- 5Institute of Bioorganic Chemistry (RAS), Russia
- 6I.M. Sechenov First Moscow State Medical University, Russia
Neuronal calcium sensor-1 (NCS-1) protein is abundantly expressed in the central nervous system and retinal neurons, where it regulates many vital processes such as synaptic transmission. It coordinates three calcium ions by EF-hands 2-4, thereby transducing Ca2+ signals to a wide range of protein targets, including G protein-coupled receptors and their kinases. Here, we demonstrate that NCS-1 also has Zn2+-binding sites, which affect its structural and functional properties upon filling. Fluorescence and circular dichroism experiments reveal the impact of Zn2+ binding on NCS-1 secondary and tertiary structure. According to atomic absorption spectroscopy and isothermal titration calorimetry studies, apo-NCS-1 has two high-affinity (4×106 M-1) and one low-affinity (2×105 M-1) Zn2+-binding sites, whereas Mg2+-loaded and Ca2+-loaded forms (which dominate under physiological conditions) bind two zinc ions with submicromolar affinity. Metal competition analysis and circular dichroism studies suggest that Zn2+-binding sites of apo- and Mg2+-loaded NCS-1 overlap with functional EF-hands of the protein. Consistently, high Zn2+ concentrations displace Mg2+ from the EF-hands and decrease the stoichiometry of Ca2+ binding. Meanwhile, one of the EF-hands of Zn2+-saturated NCS-1 exhibits a 14-fold higher calcium affinity, which increases the overall calcium sensitivity of the protein. Based on QM/MM molecular dynamics simulations, Zn2+ binding to Ca2+-loaded NCS-1 could occur at EF-hands 2 and 4. The high-affinity zinc binding increases the thermal stability of Ca2+-free NCS-1 and favours the interaction of its Ca2+-loaded form with target proteins, such as dopamine receptor D2R and GRK1. In contrast, low-affinity zinc binding promotes NCS-1 aggregation accompanied by the formation of twisted rope-like structures. Altogether, our findings suggest a complex interplay between magnesium, calcium and zinc binding to NCS-1, leading to the appearance of multiple conformations of the protein, in turn modulating its functional status.
Keywords: Neuronal calcium sensor-1, Zinc, Calcium, Magnesium, EF-hand motif, dopamine receptor D2R, GRK1, protein aggregation, neurodegeneration
Received: 21 Jul 2018;
Accepted: 28 Nov 2018.
Edited by:JOSE R. NARANJO, Spanish National Research Council (CSIC), Spain
Reviewed by:Alexander Dizhoor, Salus University, United States
Yogendra Sharma, Centre for Cellular and Molecular Biology (CSIR), India
Copyright: © 2018 Tsvetkov, Roman, Baksheeva, Nazipova, Shevelyova, Vladimirov, Buyanova, Zinchenko, Zamyatnin Jr., Devred, Golovin, Permyakov and Zernii. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. Evgeni Y. Zernii, Lomonosov Moscow State University, Moscow, 119992, Russia, firstname.lastname@example.org