Abstract
The overarching paradigm for the activation of class III and V receptor tyrosine kinases (RTKs) prescribes cytokine-mediated dimerization of the receptor ectodomains and homotypic receptor-receptor interactions. However, structural studies have shown that the hematopoietic receptor FLT3, a class III RTK, does not appear to engage in such receptor-receptor contacts, despite its efficient dimerization by dimeric FLT3 ligand (FL). As part of efforts to better understand the intricacies of FLT3 activation, we sought to engineer a monomeric FL. It was found that a Leu27Asp substitution at the dimer interface of the cytokine led to a stable monomeric cytokine (FLL27D) without abrogation of receptor binding. The crystal structure of FLL27D at 1.65 Å resolution revealed that the introduced point mutation led to shielding of the hydrophobic footprint of the dimerization interface in wild-type FL without affecting the conformation of the FLT3 binding site. Thus, FLL27D can serve as a monomeric FL variant to further interrogate the assembly mechanism of extracellular complexes of FLT3 in physiology and disease.
Highlights
30% of newly diagnosed patients with acute myeloid leukemia (AML) harbor mutations in FMS-like tyrosine kinase receptor 3 (FLT3), which confer a poor disease prognosis
The receptor is a member of the class III tyrosine kinase receptors (RTK-IIIs), which include CSF-1R, KIT, PDGFR and PDGFR, which are all characterized by a conserved modular architecture featuring an extracellular domain (ECD) comprising five Ig-like domains, a single membrane-spanning helix (TM) followed by a juxtamembrane (JM) region, and an intracellular tyrosine kinase domain (TKD) (Fig. 1a; Lemmon & Schlessinger, 2010; Verstraete & Savvides, 2012)
While the intracellular activation mechanism of receptor tyrosine kinases (RTKs)-III is conserved in all RTK-IIIs, it has been shown that ligand binding to the membrane-distal domains takes place by homotypic receptor– receptor contacts that are mediated by the membraneproximal Ig-like domains D4 and/or D5
Summary
30% of newly diagnosed patients with acute myeloid leukemia (AML) harbor mutations in FMS-like tyrosine kinase receptor 3 (FLT3), which confer a poor disease prognosis (recently reviewed by Daver et al, 2019). The receptor is a member of the class III tyrosine kinase receptors (RTK-IIIs), which include CSF-1R, KIT, PDGFR and PDGFR , which are all characterized by a conserved modular architecture featuring an extracellular domain (ECD) comprising five Ig-like domains, a single membrane-spanning helix (TM) followed by a juxtamembrane (JM) region, and an intracellular tyrosine kinase domain (TKD) (Fig. 1a; Lemmon & Schlessinger, 2010; Verstraete & Savvides, 2012) Due to their highly similar build and the dimeric nature of their cognate cytokine ligands, RTK-IIIs are thought to be activated by similar mechanisms (Verstraete & Savvides, 2012). We hypothesized that a nonactivating, albeit receptor-binding-competent, variant of FL could lead to the stabilization of mechanistically relevant conformational states of FLT3
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
