A nanosecond fluorescence depolarization study on the segmental flexibility of receptor-bound immunoglobulin E.
Time-resolved fluorescence anisotropy measurements have been used to examine the segmental flexibility of anti-dansyl immunoglobulin E (IgE) bound to its high-affinity receptor on membrane vesicles from rat basophilic leukemia cells. Although IgE in this complex exhibits only a restricted angular range of segmental motion, much of this restricted motion occurs on a relatively rapid time scale. A fast component of motion with a rotational correlation time of 15-35 ns may correspond to the twisting of Fab segments about their major axis. Intermolecular cross-linking by a short bivalent ligand, N,N'-didansylcadaverine, results in complete loss of this segmental motion. Solubilization of monomeric IgE-receptor complexes using a zwitterionic detergent results in a time-dependent anisotropy decay that exhibits both a fast component and a slower component that is intermediate between the decay for soluble and membrane-bound forms of IgE at long times after excitation. These results are discussed in terms of a model in which binding of IgE to its membrane-bound receptor restricts not only its global rotation but also its slower modes of segmental flexibility as well, while allowing its Fab segments to undergo rapid reorientation within a limited angular range.
Holowka
D
D
Department of Chemistry, Cornell University, Ithaca, New York 14853.
Wensel
T
T
Baird
B
B
D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte / Q000378:metabolism*; D001666:Binding Sites, Antibody; D005454:Fluorescence Polarization; D007073:Immunoglobulin E / Q000378:metabolism*; D015471:Leukemia, Basophilic, Acute / Q000276:immunology / Q000378:metabolism; D009038:Motion; D051381:Rats; D011961:Receptors, Fc / Q000378:metabolism*; D017455:Receptors, IgE; D012995:Solubility
D000944:Antigens, Differentiation, B-Lymphocyte; D011961:Receptors, Fc; D017455:Receptors, IgE; D007073:Immunoglobulin E