Kinetics of the reaction of a myelin basic protein peptide with soluble IAu

The kinetics of formation and dissociation of IAu-peptide complexes have been examined in the absence of detergent, using a glycosylphosphatidylinositol (GPI)-linked form of IAu. The GPI-linked form contains a lipid membrane anchor which can be specifically cleaved by phosphatidylinositol-specific phospholipase C to yield a water-soluble form of IAu. We find rapid binding of the myelin basic protein (MBP) peptide analogue Ac(1-14)A4C15 to IAu, as well as rapid dissociation of IAu-MBP peptide complexes at neutral pH in the absence of detergent. The reaction kinetics of the water-soluble and detergent-solubilized complexes are the same to within experiment error. In the presence of this MBP peptide, Ac(1-14)A4C15, cells transfected with native IAu as well as cells transfected with a GPI-linked form of IAu are functional in stimulating T-helper hybridoma cells.