Structural evaluation of potent NKT cell agonists: implications for design of novel stimulatory ligands.
Natural killer T (NKT) cells are a subset of T cells that are activated by CD1d-glycolipid complexes through a semi-invariant alphabeta T cell receptor (NKT TCR). Upon activation, NKT cells secrete regulatory cytokines that are implicated in T helper cell responses. alpha-Galactosylceramide (alpha-GalCer) is a potent NKT cell agonist when presented by CD1d. Phenyl ring substitutions of the alpha-GalCer fatty acid moiety were recently found to be superior in eliciting regulatory cytokines. Crystal structures of four new mouse CD1d-lipid complexes (five structures), a new PBS-25 complex, and CD1d with an endogenous ligand, at 1.6-1.9 A resolution, reveal that the alpha-GalCer phenyl analogues impart minor structural differences to the A'-pocket, while the sphingosine and galactose moieties, important for NKT TCR recognition, remain virtually unchanged. The observed differences in cytokine-release profiles appear to be associated with increased stability of the CD1d-glycolipid complexes rather than increased affinity for the NKT TCR. Furthermore, comparison of mouse CD1d-glycolipid complexes in different crystallographic space groups reveals considerable conformational variation, particularly above the F'-pocket, the primary site of interaction with the NKT TCR. We propose that modifications of the sphingosine moiety or other substitutions that decrease alpha-GalCer flexibility would stabilize the F'-pocket. Such compounds might then increase CD1d affinity for the NKT TCR and further enhance the stimulatory and regulatory properties of alpha-GalCer derivatives.
Schiefner
André
A
Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
Fujio
Masakazu
M
Wu
Douglass
D
Wong
Chi-Huey
CH
Wilson
Ian A
IA
D000818:Animals; D055610:Antigens, CD1d / Q000737:chemistry / Q000276:immunology*; D018360:Crystallography, X-Ray; D006017:Glycolipids / Q000737:chemistry / Q000276:immunology*; D008024:Ligands; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D008958:Models, Molecular; D055611:Natural Killer T-Cells / Q000276:immunology*; D018583:Pliability; D017433:Protein Structure, Secondary; D055672:Static Electricity
D055610:Antigens, CD1d; D006017:Glycolipids; D008024:Ligands