Blood, Vol. 94 No. 11 (December 1), 1999:
pp. 3748-3753
Kinetic Resolution of Two Mechanisms for High-Affinity
Granulocyte-Macrophage Colony-Stimulating Factor Binding to Its
Receptor
Linghao Niu,
David W. Golde,
Juan Carlos Vera, and
Mark L. Heaney
From the Program in Molecular Pharmacology and Therapeutics and
Department of Medicine, Memorial Sloan-Kettering Cancer Center, New
York, NY.
Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an
important hematopoietic cytokine that exerts its effects by interaction
with the GM-CSF receptor (GMR) on the surface of responsive cells. The
GM-CSF receptor consists of two subunits: GMR
, which binds GM-CSF
with low affinity, and GMR
, which lacks intrinsic ligand-binding
capability but complexes with GMR to form a high-affinity receptor
(GMR/). We conducted dynamic kinetic analyses of GM-CSF receptors
to define the role of GMR in the interaction of ligand and receptor.
Our data show that GMR/ exhibits a higher kon than
GMR, indicating that GMR facilitates ligand acquisition to the
binding pocket. Heterogeneity with regard to GM-CSF dissociation from
GMR/ points to the presence of loose and tight ligand-receptor complexes in high-affinity binding. Although the loose complex has a
koff similar to GMR, the lower koff
indicates that GMR inhibits GM-CSF release from the tight receptor
complex. The two rates of ligand dissociation may provide for discrete
mechanisms of interaction between GM-CSF and its high-affinity
receptor. These results show that the subunit functions to
stabilize ligand binding as well as to facilitate ligand acquisition.
