Structural insights into the activation initiation of full-length mGlu1
- PDF / 1,009,740 Bytes
- 6 Pages / 595.276 x 785.197 pts Page_size
- 70 Downloads / 194 Views
Protein & Cell
LETTER
Dear Editor, Glutamate is the main excitatory neurotransmitter in the human brain, and it exerts diverse responses through ionotropic glutamate receptors (iGluRs) and metabotropic glutamate receptors (mGluRs) (Nakanishi and Masu, 1994). mGluRs are members of the C family of GPCRs, and are divided into three groups based on G protein coupling, sequence homology, and ligand selectivity (Stansley and Conn, 2019). mGlu1 and mGlu5 belong to group I and predominantly couple to Gq/11. They are postsynaptic glutamate receptors that respond much slower than the typical postsynaptic AMPA or NMDA-type iGluRs (millisecond timescale) (Scheefhals and MacGillavry, 2018). mGlu1 is involved in multiple physiological processes in the central nervous system (CNS) and is a promising therapeutic target for treating CNS associated disorders. Notably, positive allosteric modulators (PAMs) of mGlu1 show the selectivity in the striatum dopamine signaling inhibition and hold the potential for treating schizophrenia with fewer side effects (Stansley and Conn, 2019). Constitutive homo- or hetero-dimerization is the defining feature of class C GPCRs, and mGluRs form homodimers mediated by the intermolecular disulfide bond within the N-terminal extracellular domain (ECD) (Wu et al., 2014). The large ECD of mGluRs can be divided into two parts: the venus flytrap (VFT) domain and the cysteine-rich domain (CRD) (Muto et al., 2007). In contrast to GPCRs of other classes, ligands bind to the orthosteric site in the VFT domain or the allosteric site in the 7TM domain (Pin and Bettler, 2016). So far, crystal structures have been determined for the orthosteric ligand bound (agonist or antagonist) and ligand free form of VFT domain of mGlu1 (Kunishima et al., 2000; Tsuchiya et al., 2002), and the negative modulator (NAM) bound 7TM domain of mGlu1 (Wu et al., 2014). These structures provide clues about the dimerization of the VFT domain and high-resolution architecture of the mGlu1 transmembrane region. However, the full-length structure of mGlu1 is still unknown and the agonist-induced conformational transition of mGlu1 remains elusive due to the missing apo and active full-length mGlu1 structures. Here, we present two full-length mGlu1 structures in the apo and © The Author(s) 2020
intermediate active states at 3.96 Å and 3.65 Å, respectively, using cryo-EM single particle analysis. This study captures a new intermediate state of mGluRs and provides additional insights into the dynamic activation process of mGluRs. To enhance the expression and stability of mGlu1, the wild-type mGlu1 was modified by N- and C-terminal truncations and the optimized construct was expressed in the insect cell system (See Supplementary Materials). To seek the mGlu1 active conformation, the orthosteric agonist L-Quisqualic acid together with PAM Ro 67-4853 were added during protein purification. L-Quisqualic acid is a group I mGluRs preferred agonist that shows higher potency than glutamate (Schoepp et al., 1999), and Ro 67-4853 is a selective PAM of mGlu
Data Loading...
