Journal
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Volume 389, Issue 2, Pages 388-393Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.bbrc.2009.09.002
Keywords
Intrinsically disordered protein; T cell receptor; Membrane binding; Conformational change; Membrane model
Categories
Funding
- NIH/NIAID, University of Massachusetts Center for AIDS Research [P30 AI42845-08]
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Intrinsically disordered cytoplasmic domains of T cell receptor (TCR) signaling subunits including zeta(cyt) and CD3 epsilon(cyt) all contain one or more copies of an immunoreceptor tyrosine-based activation motif (ITAM), tyrosine residues of which are phosphorylated upon receptor triggering. Membrane binding-induced helical folding of zeta(cyt) and CD3 epsilon(cyt) ITAMs is thought to control TCR activation. However, the question whether or not lipid binding of zeta(cyt) and CD3 epsilon(cyt) is necessarily accompanied by a folding transition of ITAMs remains open. In this study, we investigate whether the membrane binding mechanisms of zeta(cyt) and CD3 epsilon(cyt) depend on the membrane model used. Circular dichroic and fluorescence data indicate that binding of zeta(cyt) and CD3 epsilon(cyt) to detergent micelles and unstable vesicles is accompanied by a disorder-to-order transition, whereas upon binding to stable vesicles these proteins remain unfolded. Using electron microscopy and dynamic light scattering, we show that upon protein binding, unstable vesicles fuse and rupture. In contrast, stable vesicles remain intact under these conditions. This suggests different membrane binding modes for zeta(cyt) and CD3 epsilon(cyt) depending on the bilayer stability: (1) coupled binding and folding, and (2) binding without folding. These findings explain the long-standing puzzle in the literature and highlight the importance of the choice of an appropriate membrane model for protein-lipid interactions Studies. (C) 2009 Elsevier Inc. All rights reserved.
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