CRYSTAL-STRUCTURE OF A CYTOKINE-BINDING REGION OF GP130

The structure of the cytokine-binding homology region of the cell surf ace receptor gp130 has been determined by X-ray crystallography at 2.0 Angstrom resolution. The beta sandwich structure of the two domains c onforms to the topology of the cytokine receptor superfamily. This fir st structure of an uncomplexed receptor exhibits a similar L-shaped qu aternary structure to that of ligand-boumd family members and suggests a limited flexibility in relative domain orientation of some 3 degree s. The putative ligand-binding loops are relatively rigid, with a phen ylalanine side chain similarly positioned to exposed aromatic residues implicated in ligand binding for other such receptors. The positionin g and structure of the N-terminal portion of the polypeptide chain hav e implications for the structure and function of cytokine receptors, s uch as gp130, which contain an additional N-terminal immunoglobulin-li ke domain.