Chris Habrian

All Publications

• Homo- and hetero-dimeric subunit interactions set affinity and efficacy in metabotropic glutamate receptors. Nature communications Habrian, C., Latorraca, N., Fu, Z., Isacoff, E. Y. 2023; 14 (1): 8288

  Abstract

  Metabotropic glutamate receptors (mGluRs) are dimeric class C G-protein-coupled receptors that operate in glia and neurons. Glutamate affinity and efficacy vary greatly between the eight mGluRs. The molecular basis of this diversity is not understood. We used single-molecule fluorescence energy transfer to monitor the structural rearrangements of activation in the mGluR ligand binding domain (LBD). In saturating glutamate, group II homodimers fully occupy the activated LBD conformation (full efficacy) but homodimers of group III mGluRs do not. Strikingly, the reduced efficacy of Group III homodimers does not arise from differences in the glutamate binding pocket but, instead, from interactions within the extracellular dimerization interface that impede active state occupancy. By contrast, the functionally boosted mGluR II/III heterodimers lack these interface 'brakes' to activation and heterodimer asymmetry in the flexibility of a disulfide loop connecting LBDs greatly favors occupancy of the activated conformation. Our results suggest that dimerization interface interactions generate substantial functional diversity by differentially stabilizing the activated conformation. This diversity may optimize mGluR responsiveness for the distinct spatio-temporal profiles of synaptic versus extrasynaptic glutamate.

  View details for DOI 10.1038/s41467-023-44013-4

  View details for PubMedID 38092773

  View details for PubMedCentralID 6535337

• Step-wise activation of a Family C GPCR. bioRxiv : the preprint server for biology Kumar, K. K., Wang, H., Habrian, C., Latorraca, N. R., Xu, J., O'Brien, E. S., Zhang, C., Montabana, E., Koehl, A., Marqusee, S., Isacoff, E. Y., Kobilka, B. K. 2023

  Abstract

  Metabotropic glutamate receptors belong to a family of G protein-coupled receptors that are obligate dimers and possess a large extracellular ligand-binding domain (ECD) that is linked via a cysteine-rich domain (CRDs) to their 7-transmembrane (TM) domain. Upon activation, these receptors undergo a large conformational change to transmit the ligand binding signal from the ECD to the G protein-coupling TM. In this manuscript, we propose a model for a sequential, multistep activation mechanism of metabotropic glutamate receptor subtype 5. We present a series of structures in lipid nanodiscs, from inactive to fully active, including agonist-bound intermediate states. Further, using bulk and single-molecule fluorescence imaging we reveal distinct receptor conformations upon allosteric modulator and G protein binding.

  View details for DOI 10.1101/2023.08.29.555158

  View details for PubMedID 37693614

  View details for PubMedCentralID PMC10491200

• Negative allosteric modulation of the glucagon receptor by RAMP2. Cell Krishna Kumar, K., O'Brien, E. S., Habrian, C. H., Latorraca, N. R., Wang, H., Tuneew, I., Montabana, E., Marqusee, S., Hilger, D., Isacoff, E. Y., Mathiesen, J. M., Kobilka, B. K. 2023; 186 (7): 1465-1477.e18

  Abstract

  Receptor activity-modifying proteins (RAMPs) modulate the activity of many Family B GPCRs. We show that RAMP2 directly interacts with the glucagon receptor (GCGR), a Family B GPCR responsible for blood sugar homeostasis, and broadly inhibits receptor-induced downstream signaling. HDX-MS experiments demonstrate that RAMP2 enhances local flexibility in select locations in and near the receptor extracellular domain (ECD) and in the 6th transmembrane helix, whereas smFRET experiments show that this ECD disorder results in the inhibition of active and intermediate states of the intracellular surface. We determined the cryo-EM structure of the GCGR-Gs complex at 2.9 Å resolution in the presence of RAMP2. RAMP2 apparently does not interact with GCGR in an ordered manner; however, the receptor ECD is indeed largely disordered along with rearrangements of several intracellular hallmarks of activation. Our studies suggest that RAMP2 acts as a negative allosteric modulator of GCGR by enhancing conformational sampling of the ECD.

  View details for DOI 10.1016/j.cell.2023.02.028

  View details for PubMedID 37001505

• Negative allosteric modulation of the glucagon receptor by RAMP2 O'Brien, E. S., Kumar, K., Habrian, C., Latorraca, N. R., Wang, H., Tuneew, I., Montabana, E., Marqusee, S., Hilger, D., Isacoff, E. Y., Mathiesen, J. M., Kobilka, B. K. CELL PRESS. 2023: 161A

  View details for Web of Science ID 000989629700786

• Negative allosteric modulation of the glucagon receptor by RAMP2. Biophysical journal O'Brien, E. S., Krishna Kumar, K., Habrian, C., Latorraca, N. R., Wang, H., Tuneew, I., Montabana, E., Marqusee, S., Hilger, D., Isacoff, E. Y., Mathiesen, J. M., Kobilka, B. K. 2023; 122 (3S1): 161a

  View details for DOI 10.1016/j.bpj.2022.11.1023

  View details for PubMedID 36782752