【Research News】Liu Jianfeng's team from the School of Life Sciences, Huazhong University of Science and Technology found that GPCR oligomers lead to a new mechanism of biased activation

On October 26, 2022, Professor Jianfeng's research team from the School of Life Sciences and the Key Laboratory of Molecular Biophysics of the Ministry of Education published an online publication entitled "Biased signaling due to oligomerization of the G protein-coupled platelet-activating" online in Nature Communications factor receptor" (G-protein-coupled biased signaling of platelet activator receptors results from receptor oligomerization
).

G protein-coupled receptor (GPCR) is a family of receptors with seven transmembrane helical (7TM) structures on the cell membrane, and it is also the largest membrane protein family in the human body, which is widely involved in the occurrence and development of diseases and is an important drug target
.
One-third of the drugs on the market target GPCRs and their signaling pathways
.
GPCRs include four types
: A, B, C, and F.
Among them, Class A GPCR has the largest
number of members.
In addition to the function of class C GPCRs that must form dimers, other GPCRs can activate downstream signals in the form of monomers, and have also been found to form dimers or oligomers
.
However, the correlation between the form of polymerization and physiological function and signal regulation is not clear
.
The downstream signaling of GPCR is mainly mediated
by G proteins and β-arrestin.
The balance between the two signals can be regulated
by biased ligands.
Biased ligands selectively activate certain signals while reducing or blocking others, providing direction
for the development of drugs with few side effects.
However, the internal mechanism of GPCR bias signaling has yet to be elucidated
.

The platelet-activating-factor receptor (PAFR) belongs to class A GPCRs and is closely related to
platelet aggregation and inflammatory response.
Stimulated by the endogenous ligand PAF, PAFR can activate Gq and Gi proteins and recruit β-arrestin to cause receptor internalization
.
In 2017, Jianfeng Liu's research team participated in the functional detection of PAFR crystal structure in inactivated states analyzed by Wu Beili/Zhao Qiang/Zhang Kai of the Chinese Academy of Sciences, and verified the binding pocket between ligand and PAFR (Nat.
Struct.
Mol.
Biol.
, 2017), however how PARF activates different signaling pathways downstream remains to be studied
.
In this research project, Liu Jianfeng's research team used PAFR as a representative of class A GPCR, and found that PAFR had monomers, dimers and oligomers on the cell membrane at low expression levels through single-molecule imaging and bioluminescence resonance energy transfer technology Mixed form
.
The SNAP-based cysteine crosslinking technique established by the team in the class C GPCR dimer study was used (Nat Chem Biol.
, 2015; Nat Commun.
, 2019; PNAS.
, 2020), found that PAFR forms dimers by TM1, TM4, and TM5 interactions, and transmembrane region conformational rearrangement does not occur between the two monomers during activation, which is different
from the relative structural characteristics of TM6 and TM6 when class C GPCR dimers are activated.
Then, when PAFR is locked in dimers and oligomers, PAF can biasively induce stronger G protein signaling activation and reduce the recruitment of β-arrestin and the associated receptor internalization process
。 At the same time, the recruitment of β-arrestin affects the bias of downstream signals by reducing the PAFR dimerization and oligomerization states (Figure 1), which provides a new mechanism for the regulation of GPCR bias signals and a new direction for biased drug development
。 Finally, in a natural genetic mutant of PAFR, they found that the ratio of dimers to oligomers increased, altering the sum of G proteins β-arrestin signal bias, which provides physiological significance
for the presence of different polymerization forms of GPCRs.

Figure 1: Schematic of GPCR generating bias signals through dimerization and oligomerization

Liu Junke, a postdoctoral fellow at the School of Life Science and Technology, Huazhong University of Science and Technology, and Tang Hengmin, a doctoral student, are the co-first authors
of this research paper.
Professor Liu Jianfeng of Huazhong University of Science and Technology, researcher Ji Wei of the Institute of Biophysics, Chinese Academy of Sciences, and Professor J-P Pin and P Rondard of the French Institute of Functional Genomics are the co-corresponding authors
.
The research was supported
by the National Key R&D Program of the Ministry of Science and Technology, the National Natural Science Foundation of China and the "111 Introduction Program" of the Ministry of Education.

This work is another important discovery
of Liu Jianfeng's team in the study of GPCR activation mechanism.
Professor Liu Jianfeng has been engaged in the research of membrane protein structure and function for a long time, especially on the structural and functional correlation of GPCR dimers, the dynamic activation mechanism of membrane receptors and downstream signal transduction pathways, etc.
, and has successively been the corresponding author in Cell x2 and Nature^x2 、NatureChemicalBiology^x2、Nature Communications^x3、Cell Research^x2、 ScienceAdvances、PNAS^x2、ScienceSignaling , eLife^x2 and other internationally renowned journals published a series of research papers
.
This study demonstrates the new mode of action of GPCR dimers and oligomers and the new mechanism of biased signal regulation, and expands the signal integration theory
of GPCR.

Original link: https://doi.
org/10.
1038/s41467-022-34056-4