Abstract
Homodimeric class 1 cytokine receptors include the erythropoietin (EPOR), thrombopoietin (TPOR), granulocyte colony-stimulating factor 3 (CSF3R), growth hormone (GHR), and prolactin receptors (PRLR). They are cell-surface single-pass transmembrane (TM) glycoproteins that regulate cell growth, proliferation, and differentiation and induce oncogenesis. An active TM signaling complex consists of a receptor homodimer, one or two ligands bound to the receptor extracellular domains and two molecules of Janus Kinase 2 (JAK2) constitutively associated with the receptor intracellular domains. Although crystal structures of soluble extracellular domains with ligands have been obtained for all the receptors except TPOR, little is known about the structure and dynamics of the complete TM complexes that activate the downstream JAK-STAT signaling pathway. Three-dimensional models of five human receptor complexes with cytokines and JAK2 were generated using AlphaFold Multimer. Given the large size of the complexes (from 3220 to 4074 residues), the modeling required a stepwise assembly from smaller parts with selection and validation of the models through comparisons with published experimental data. The modeling of active and inactive complexes supports a general activation mechanism that involves ligand binding to a monomeric receptor followed by receptor dimerization and rotational movement of the receptor TM α-helices causing proximity, dimerization, and activation of associated JAK2 subunits. The binding mode of two eltrombopag molecules to TM α-helices of the active TPOR dimer was proposed. The models also help elucidating the molecular basis of oncogenic mutations that may involve non-canonical activation route. Models equilibrated in explicit lipids of the plasma membrane are publicly available.
Competing Interest Statement
The authors have declared no competing interest.
Abbreviations
- AFM
- AlphaFold Multimer
- CHM
- cytokine homology module
- CRT
- calreticulin
- CSF3
- granulocyte colony-stimulating factor
- CSF3R
- granulocyte colony-stimulating factor 3 receptor
- CSH1
- placental lactogen or chorionic somatomammotropin hormone 1
- ECD
- extracellular domain
- EPOR
- erythropoietin receptor
- ET
- essential thrombocythemia
- FERM
- four-point-one, ezrin, radixin, moesin
- FnIII
- fibronectin type III
- GH1
- somatotropin
- GHR
- growth hormone receptor
- GOF
- gain-of-function (mutation)
- JAK2
- Janus Kinase 2
- ICD
- intracellular domain
- IL
- interleukin
- LOF
- loss-of-function (mutation)
- MD
- molecular dynamics
- MPN
- myeloproliferative neoplasms
- NVT
- dynamics, constant number, constant-volume, and constant-temperature simulation
- NPT
- ensemble, isothermal-isobaric ensemble
- PK
- pseudokinase
- PMF
- primary myelofibrosis
- PRLR
- prolactin receptor
- PV
- polycythemia vera
- SH2L
- Src-homology 2-like SHP, tyrosine phosphatase
- SOCS
- suppressors of cytokine signaling
- TPOR
- thrombopoietin receptor
- TK
- tyrosine kinase
- TM
- transmembrane
- TMD
- transmembrane domain
- TM-JM
- transmembrane and juxtamembrane regions.