The biophysical basis of receptor tyrosine kinase ligand functional selectivity: Trk-B case study

Abstract

Tropomyosin receptor kinase B (Trk-B) belongs to the second largest family of membrane receptors, Receptor Tyrosine Kinases (RTKs). Trk-B is known to interact with three different neurotrophins: Brain-Derived Neurotrophic Factor (BDNF), Neurotrophin-4 (NT-4), and Neurotrophin-3 (NT-3). All three neurotrophins are involved in survival and proliferation of neuronal cells, but each induces distinct signaling through Trk-B. We hypothesize that the different biological effects correlate with differences in the interactions between the Trk-B receptors, when bound to different ligands, in the plasma membrane. To test this hypothesis, we use quantitative FRET to characterize Trk-B dimerization in response to NT-3 and NT-4 in live cells, and compare it to the previously published data for Trk-B in the absence and presence of BDNF. Our study reveals that the distinct Trk-B signaling outcomes are underpinned by both different configurations and different stabilities of the three ligand-bound Trk-B dimers in the plasma membrane.

Interaction between the transmembrane domains of neurotrophin receptors p75 and TrkA mediates their reciprocal activation

“…The finding that mutations in the p75 protein interface, as shown here with the p75-AGA mutant, impact the TrkA activation and supports the requirement of specific TMD interactions in the neurotrophin receptors. As it has been shown recently, NGF binding can induce the rotation of the TrkA TM dimer form the inactive to the active interface (36,51). This conformational change is supported by our FRET analysis, which reveals that NGF binding alters the TrkA-p75 heterocomplex that we observed in the absence of ligand.…”

A molecular mechanism for the generation of ligand-dependent differential outputs by the epidermal growth factor receptor

“…In this way, EGF and TGF-α can generate different responses from EGFR by differentially modulating the structure of the junction point between the extracellular module and the transmembrane helices, altering the balance between alternative dimeric configurations of the transmembrane helices ( Figure 10B ). A lack of rigidity in the linkage between the extracellular module and the transmembrane helices is emerging as a common feature in receptor tyrosine kinases ( Diwanji et al, 2021 ; Li et al, 2019 ; Lu et al, 2010 ; Uchikawa et al, 2019 ; Zhang et al, 2020 ), and the mechanism we have defined, involving modulation of the separation of the tips of the extracellular modules, could potentially be utilized by other receptor tyrosine kinases to generate ligand-specific signaling outputs ( Ahmed et al, 2020 ).…”

Quantitative characterization of tetraspanin 8 homointeractions in the plasma membrane

“…Tspan8 has one of the highest dissociation constants quantitatively measured in living cells, and thus it exhibits one of the weakest self-interaction propensity among membrane proteins. (26,40,(47)(48)(49)(50)(51)(52) Association rates are believed to be diffusion limited, and thus similar for all proteins, while dissociation rates reflect the strength of the interactions. (61) Thus, the measured high dissociation constant implies high dissociation rates and therefore short lifetimes of Tspan dimers.…”