Characterization of {alpha}X I-domain binding to Thy-1
- Divisions of Science Education and Biology, Kangwon National University, Choonchun, Kangwon (Korea, Republic of)
- FONDAP Center for Molecular Studies of the Cell, ICBM-Faculty of Medicine, University of Chile, Santiago (Chile)
The {beta}2 integrins are found exclusively in leukocytes and they are composed of a common {beta} chain, CD18, and one of four unique {alpha} chains, CD11a ({alpha}L subunit), CD11b ({alpha}M subunit), CD11c ({alpha}X subunit), or CD11d ({alpha}D subunit). {alpha}X-{beta}2 which binds several ligands including fibrinogen and iC3b is expressed in monocytes/macrophages and dendritic cells playing an important role in the host defense. Despite the unique characteristics on expression and regulation, {alpha}X-{beta}2 is less functionally characterized than other {beta}2 integrins. To understand the biological function of {alpha}X-{beta}2 more, we tested the possibility that {alpha}X-{beta}2 binds Thy-1, a membrane protein involved in cell adhesion and signaling regulation in neurons and T cells. Here we report that a ligand binding moiety of {alpha}X-{beta}2, the I-domain, bound Thy-1 in a specific and divalent cation-dependent manner. The dissociation constant (K{sub D}) of {alpha}X I-domain binding to Thy-1 was 1.16 {mu}M and the affinity of the binding was roughly 2-fold higher than that of {alpha}M I-domain. Amino acid substitutions on the {beta}D-{alpha}5 of {alpha}X I-domain (D249, KE243/244) showed low affinities for Thy-1 while other point mutations on {alpha}3-{alpha}4 and {beta}E-{alpha}6 loops of I-domain did not, suggesting that Thy-1 recognizes the portion of a {beta}D-{alpha}5 loop, possibly {alpha}5 helix. Taken together, these results indicate that {alpha}X-{beta}2 specifically interacts with Thy-1. Additionally, kinetic analysis reveals a moderate affinity interaction in the presence of divalent cations. Given the reported role of Thy-1 in the regulation of T cell homeostasis and proliferation, it is tempting to speculate that {alpha}X-{beta}2 may be involved in Thy-1 function.
- OSTI ID:
- 20709216
- Journal Information:
- Biochemical and Biophysical Research Communications, Vol. 331, Issue 2; Other Information: DOI: 10.1016/j.bbrc.2005.04.006; PII: S0006-291X(05)00754-0; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0006-291X
- Country of Publication:
- United States
- Language:
- English
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