New publication sheds light onto the molecular basis of neurotransmitter signaling

A new paper led by Alex Luebbers in the Garcia-Marcos Lab dissects the molecular basis for how GINIP, a Gαi-interacting protein in neurons involved in controlling pain and seizures, modulates GPCR responses triggered by neurotransmitters. GINIP mimics how G-protein signaling effectors bind to Gα subunits via its PHD domain to differentially scale discrete G-protein signaling branches. The paper has been published in Structure (, and was previously posted on bioRxiv (

This paper builds and explands on another paper recently published in the same lab establishing that the neuronal protein GINIP shapes GPCR inhibitory neuromodulation via a unique mechanism of G-protein regulation that controls pain and seizure susceptibility (Park, Luebbers, et al Molecular Cell, 2023). However, the molecular basis of this mechanism remained ill-defined because the structural determinants of GINIP responsible for binding and regulating G proteins were not known. The newly published paper combined hydrogen-deuterium exchange mass spectrometry, computational structure predictions, biochemistry, and cell-based biophysical assays to demonstrate an effector-like binding mode of GINIP to Gαi. These findings explain the molecular basis for a post-receptor mechanism of G-protein regulation that fine-tunes inhibitory neuromodulation.

This paper features collaborations with the labs of Stephen Eyles at UMass-Amherst and of Joshua Levitz at Weill Cornell.

New Publication from the Garcia-Marcos Lab: Coordinating signaling responses in neurons

The Garcia-Marcos Lab has recently published a study in Molecular Cell (; prepint in: titled “Fine-tuning GPCR-mediated neuromodulation by biasing signaling through different G protein subunits”. The paper describes how different signaling responses triggered by the same neurotransmitter receptor must be carefully scaled to ensure proper brain function. They found that the protein named GINIP shifts the balance of two different G protein sub-species activated simultaneously by G protein-coupled receptors (GPCRs), a large family of surface receptors that respond many neurotransmitters and neuropeptides, including GABA, dopamine, serotonin, or opioids. This mechanism operates in synapses that dampen neurotransmission and, when disabled, results in increased seizure susceptibility in mouse models. These findings have important implications for the fundamental understanding of neuronal communication and for the development of new therapeutic agents that act on GPCRs.

This work was co-led by Jong-Chan Park (Postdoc) and Alex Luebbers (Graduate Student) with collaborations from the Martemyanov Lab at UF Scripps Biomedical Research Institute and the Yano Lab at Northeastern University, and has been highlighted by Molecular Cell ( and Science Signaling (

New Publication: The Garcia-Marcos lab, in collaboration with members of the Department of Chemistry at Boston University and the CSIC-CIB in Spain, have published in Proceeding of the National Academy of Sciences (PNAS) …

The Garcia-Marcos lab, in collaboration with members of the Department of Chemistry at Boston University and the CSIC-CIB in Spain, have published in Proceeding of the National Academy of Sciences (PNAS) the discovery of a chemical compound that specifically blocks an aberrant

mechanism of signaling in cancer cells that drives invasion and metastasis. The publication can be found here:

Human diseases frequently arise from defects in the mechanisms by which external cues are sensed and relayed to the interior of the cell. The proteins most widely targeted by existing therapeutic agents belong to a large family of cell surface receptors named G-protein-coupled receptors (GPCRs), which relay external cues by activating G-proteins in the interior of cells. Here, we report the surprising discovery of a synthetic small molecule that selectively targets G-proteins without compromising their ability to relay signals from GPCRs. Instead, this small molecule disrupts an atypical, GPCR-independent mechanism of G-protein signaling involved in cancer. This work reveals an alternative paradigm in targeting components of a signaling machinery with broad relevance in cellular communication in health and disease.

Jingyi Zhao, Ph.D (Garcia-Marcos Lab) awarded 2022 Dahod International Scholar

Congratulations to Jingyi Zhao, Ph.D. (Garcia-Marcos Lab) who was awarded 2022 Dahod International Scholar.

Jingyi, a postdoc in Dr. Mikel Garcia-Marcos’ laboratory, will characterize a small molecule inhibitor of a novel signaling mechanism that promotes breast cancer metastasis. He has identified a promising candidate molecule, named IGGi-11, that disrupts a protein signaling complex specifically present in metastatic cancer cells. He intends to further confirm the specificity of this molecule in preventing cancer cell invasiveness without overt cytotoxic effects in normal cells, and to work towards developing analog compounds with improved properties in preclinical breast cancer models.

Remi Janicot awarded American Heart Association fellowship

Remi Janicot in the Garcia-Marcos laboratory was awarded an American Heart Association (AHA) predoctoral fellowship for his project "Optical biosensor platforms for the direct interrogation of GPCR signaling in cardiovascular cells”

The goal of this project is to create new experimental tools that can transform how GPCRs are studied. The main benefit over current methods is that these tools can be easily used in cell models that are relevant to study heart or lung disease, which has been an important limitation in the field. These new experimental possibilities would open new doors for the entire cardiovascular research community. The tools designed in this project will allow to study GPCRs with fidelity and precision. This would pave the way to develop new drugs to treat life-threatening cardiac disorders.

Congratulations Remi!


Mikel Garcia-Marcos receives John Abel Award from ASPET

Congratulations to Dr. Mikel Garcia-Marcos for receiving the 2022 American Society for Pharmacology and Experimental Therapeutics (ASPET) John J. Abel Award in Pharmacology. The Abel Award is named after the founder of ASPET. It was established in 1946 to stimulate fundamental research in pharmacology and experimental therapeutics by young investigators.

The award will be presented at the ASPET Business Meeting and Awards Presentation during the ASPET Annual Meeting at Experimental Biology 2022 on Saturday, April 2 at 4:30 pm in Philadelphia. Additionally, Dr. Garcia-Marcos will deliver the Abel Award Lecture titled The Secret Life of G Proteins to open the 2022 annual meeting on Saturday, April 2 at 10:00 am in Philadelphia.

Research News: New Discovery from the Garcia-Marcos Laboratory

The Garcia-Marcos laboratory has discovered that heterotrimeric G-proteins, which are critical molecular switches in cellular communication processes, can trigger different responses in cells depending on the type of protein that activates them.

Heterotrimeric G-proteins are typically activated by G-protein-coupled receptors (GPCRs), which are the target for over one-third of drugs approved for use in the clinic. But G-proteins can also be activated by other proteins that are not GPCRs, a mechanism with important implications for human physiology and disease. The Garcia-Marcos laboratory has used an innovative approach to dissect and compare the consequences of G-protein stimulation by different activators, including GPCRs and various non-GPCR proteins. The approach leveraged a recently developed type of biosensors capable of detecting different forms of active G-proteins in living cells in real time. These were combined with engineered G-protein activator constructs that could be turned on at will with an exogenous synthetic chemical.

The main conclusion is that, contrary to previous beliefs, GPCR and non-GPCR activators elicit different forms of G-protein activation in cells. These findings have important implications in our understanding of pharmacologically actionable signaling hubs in cells, which could be leveraged to envision and design new therapeutic agents.

You can read the article here:

Garcia-Marcos M. Complementary biosensors reveal different G-protein signaling modes triggered by GPCRs and non-receptor activators. Elife. 2021 Mar 31;10:e65620. PMID: 33787494

Research discoveries: seeing G-protein signaling

The Garcia-Marcos lab has developed a suite of modular optical biosensors that enables detection of hetrotrimeric G-protein activity in live cells in contexts ranging from tumor cells to primary neurons.
Heterotrimeric G-proteins are the main transducers of signals from GPCRs, mediating the action of countless natural stimuli and therapeutic agents (about one-third of FDA-approved drugs). The new biosensors described in the paper published in Cell allow the direct detection of endogenous active G-proteins, something that had not been possible to date. This work showcases several biosensors for different G-protein subtypes and applications in multiple cellular models and research areas, from characterizing cancer-associated G-protein mutants to neurotransmitter signaling in primary neurons. This new resource will be valuable in characterizing G-protein signaling in live cells with high fidelity, temporal resolution, and convenience, propelling both fundamental research and drug discovery applications.