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Figure 1.
Figure 1. FcRn/Fc, FcRn/hdFc, and nbFc Structures(A)
FcRn/Fc complexes in the oligomeric ribbon observed in crystals
of FcRn bound to wtFc. FcRn/Fc crystals grown using human,
mouse, or rat FcRn and human, mouse, or rat Fc subclasses all
appear to contain the oligomeric ribbon packing in which FcRn
dimers are bridged by Fc homodimers. Such crystals diffract
aniostropically to 3.5 Å–8 Å, with the highest
resolution in the direction of the long axis of the FcRn
dimer.(B) Ribbon diagrams of the structures of FcRn/hdFc and
nbFc. Ordered N-linked carbohydrates are shown in ball-and-stick
representation. Disulfide bonds are yellow. Regions of disorder
in the distal C[γ]2 domain are shown as dashed lines. The
FcRn/hdFc complexes are packed in the crystals such that the
nbFc chain of the hdFc contacts an FcRn in an adjacent FcRn/hdFc
complex. This interaction involves a face of the FcRn α3 domain
opposite from the Fc binding site, and the buried surface area
(577 Å^2 total) is near the mean size buried in typical
crystal contacts (570 Å^2) (Janin, 1997), thus it is a
nonspecific interaction.(C) Close-up of the FcRn/hdFc interface.
Interface residues are turquoise (positively charged), pink
(negatively charged), and yellow (hydrophobic). The carbohydrate
attached to residue Asn-87 was omitted for clarity.(D) The
FcRn/hdFc model in the region of the N-linked carbohydrate
attached to FcRn Asn-128 superimposed on a 2.8 Å
SIGMAA-weighted 2F[o]-F[c] annealed omit electron density map
contoured at 1.0 σ.(E) Comparison of the Fc 251 to 256 loop in
the wt (red) and nb (gold) sides of hdFc (Cα rms deviation of
1.78 Å)
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