Residue 6.43 defines receptor function in class F GPCRs.

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Class F G protein-coupled receptors (GPCRs), including Frizzled (FZD) subtypes and Smoothened (SMO), are poorly understood.
• While SMO activation involves cholesterol binding to its 7TM core, FZD activation mechanisms remain largely unknown.

Purpose of the Study:

• To investigate FZD activation mechanisms using computational biology and experimental assays.
• To compare FZD activation with SMO and explore functional diversity within FZDs.

Main Methods:

• Computational biology approaches.
• Mutational analysis of FZD receptor function.
• Ligand binding assays.
• Downstream signaling assays in living cells (G protein activation, DVL2 recruitment, TOPflash activity).

Main Results:

• Frizzled receptors (FZDs) exhibit distinct activation-associated conformational changes compared to SMO.
• FZDs typically present a kinked TM6 upon activation due to residue P6.43, unlike SMO's straight TM6.
• Functional comparisons highlight significant diversity among FZD subtypes and between FZDs and SMO.

Conclusions:

• FZD and SMO receptor activation pathways differ substantially, particularly in TM6 conformation.
• The presence of P6.43 in FZDs contributes to a kinked TM6, a common GPCR feature.
• Considerable functional heterogeneity exists within the FZD family and in comparison to SMO.