10. Labelling strategies and biosensors
Over the years a variety of labelling strategies and biosensors suitable
for imaging GPCR signalling have been developed (Figure 4). Finding the
optimal probe or their combination is a cornerstone of any imaging
project because different probes have their advantages, limitations, and
areas of application. The most common labelling strategies applied in
GPCR research include the use of fluorescent ligands, FPs, direct and
ligand-directed labelling, self-labelling systems, protein conjugation
systems, quantum dots, and nanodiamonds. Existing biosensors are used to
detect a multitude of signalling processes, including ligand binding
(Rosier et al., 2021), signalling cascade activation (Maziarz et al.,
2020), GPCR conformation changes (Banerjee et al., 2022), receptor
heteromerization (Sleno et al., 2017), interactions between signalling
proteins (Olsen et al., 2020), the release of neurotransmitters
(Patriarchi et al., 2018; Sun et al., 2018), signalling in different
subcellular compartments (Irannejad et al., 2013), the production of
second messengers and their spatial localisation (Anton et al., 2022),
and many others.