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Figure 3.
(a) (4-DAPA)-HA was incubated with HLA-DR1 as described for
(4-DAPA)-RSMA[4]L, and the complex formed was purified by gel
filtration. Fluorescence of DR-(4-DAPA)-HA was compared with
that of the free peptide. (b) Activation of HA1.7 T-cell
receptor hybridoma by antigen-presenting cells pulsed with HA
(filled circles) or (4-DAPA)-HA (closed triangles) peptides.
T-cell activation reported as counts per minute (c.p.m.)
measured in a thymidine incorporation bioassay for IL-2 as
secreted by activated T cells. Error bars indicate s.d. of
triplicate measurements. (c–e) Crystal structure of
(4-DAPA)-HA bound to DR1. (c) (4-DAPA)-HA peptide shown with
surface representation of the DR1 peptide binding site, with the
4-DAPA side chain shown with yellow bonds extending down into
the P1 pocket (top); unmodified HA peptide from the crystal
structure of the DR1-HA-SEC (3B2) complex (PDB ID 1JWU) shown
after alignment of MHC peptide binding domain, with tyrosine
side chain at the P1 position shown with cyan bonds (bottom).
(d) 2F[o] - F[c] omit map of the region around the P1 pocket
with all residues shown removed from the model before map
calculation. (e) Section through the P1 pocket, showing the HA
peptide tyrosine side chain and the (4-DAPA)-HA fluorophore,
along with the corresponding ordered water molecules, colored as
in c. Panels c–e made using PyMOL^30.
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