Structure of the gamma-chain of the human IgE Fc(epsilon)R1 receptor: NMR and molecular dynamics studies

The solution structure of the 37-residue intracellular gamma-chain of the h uman Fc(epsilon)R1 receptor protein has been determined using high field H- 1 nuclear magnetic resonance (NMR) spectroscopy combined with molecular dyn amics simulations. Two closely related groups of alpha-helical structures w ere found, with disruptions of the helix between residues 20 to 24; for one group the disruption is a type I beta-turn, and in the second this region is less structured and acts as a loose 'hinge' between the alpha-helical re gions. All structures exhibited a major and a minor hydrophobic region. The two tyrosines of the ARAM (antigen recognition activation motif) consensus motif lie on a single face of the helix, as do the two hydrophobic ARAM le ucine and isoleucine residues. Three of the five threonines define a third face. These data are used to propose a model for the in vivo dimer of the g amma-chain which is consistent with the susceptibility of the tyrosines and threonines to phosphorylation as an important feature of signal transducti on.