Variable dimerization of the Ly49A natural killer cell receptor results in differential engagement of its MHC class I ligand.

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TitleVariable dimerization of the Ly49A natural killer cell receptor results in differential engagement of its MHC class I ligand.
Publication TypeJournal Article
Year of Publication2006
AuthorsDam, J, Baber, J, Grishaev, A, Malchiodi, EL, Schuck, P, Bax, A, Mariuzza, RA
JournalJ Mol Biol
Volume362
Issue1
Pagination102-13
Date Published2006 Sep 8
ISSN0022-2836
KeywordsAnimals, Antigens, Ly, Dimerization, Genes, MHC Class I, Hydrogen Bonding, Killer Cells, Natural, Lectins, C-Type, Mice, Models, Molecular, NK Cell Lectin-Like Receptor Subfamily A, Nuclear Magnetic Resonance, Biomolecular, Protein Structure, Quaternary, Protein Structure, Secondary, Receptors, NK Cell Lectin-Like
Abstract

Natural killer (NK) cells play a vital role in the detection and elimination of virally infected and tumor cells. The Ly49 family of NK receptors regulates NK cell function by sensing major histocompatibility complex (MHC) class I molecules on target cells. Previous crystal studies revealed that the Ly49A homodimer binds one MHC molecule in an asymmetric interaction, whereas the Ly49C homodimer binds two MHC in a symmetrical fashion. Moreover, the bound receptors adopt distinctly different homodimeric forms: a "closed state" for Ly49A and an "open state" for Ly49C. Steric clashes between MHC molecules would preclude the closed Ly49A dimer from engaging two MHC in the manner of the open Ly49C dimer. To determine whether individual Ly49 receptors can undergo a conformational switch enabling them to bind MHC in different ways, we carried out a solution NMR study of unbound Ly49A, aided by dipolar coupling technology. This study reveals that, in solution, unligated Ly49A adopts a symmetric, open-state, homodimer conformation similar to that seen previously for Ly49C. Hence, Ly49A can assume both closed and open states. To address whether the Ly49A dimer can bind two MHC molecules in solution, besides the binding of one MHC observed in the crystal, we carried out analytical ultracentrifugation experiments. Velocity sedimentation demonstrates that the Ly49A dimer can engage two MHC molecules in solution, in agreement with NMR results showing that unbound Ly49A exists predominantly in the open state.

DOI10.1016/j.jmb.2006.07.005
Alternate JournalJ. Mol. Biol.
PubMed ID16899255
Grant ListAI47990 / AI / NIAID NIH HHS / United States
R01 AI047990 / AI / NIAID NIH HHS / United States
/ / Intramural NIH HHS / United States