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Figure 2.
FIG. 2. The RAG2 C terminus contains a noncanonical PHD
finger. A, alignment of the RAG2 zinc finger to representative
zinc fingers from similar structural classes. The RAG2 sequence
(aa 414-487) was aligned to the indicated PHD, RING, and FYVE
finger sequences. Red circles represent zinc-binding residues
Cys-419, His-452, and His-481 of RAG2 that deviate from the PHD
finger consensus. Zn1, first zinc; Zn2, second zinc; L1 and L2,
extended segments of sequence between pairs of zinc-coordinating
residues. B, the RAG2 zinc finger is structurally most similar
to the PHD finger. Ribbon schematics compare the C-terminal zinc
finger of RAG2 to the indicated PHD, RING, and FIVE fingers. The
ligands of the two zinc ions appear as interleaved pairs in the
primary sequence of these proteins as shown in A. Two extended
polypeptide segments (L1 and L2, see A) separate equivalent
pairs of zinc-coordinating residues. The L1 segment contains the
first strand of the conserved  -sheet, whereas the
conformation of L2 varies significantly between different
proteins. The four domains are oriented in the same way using
conserved -sheet and zinc ions as
structural reference. The L2  -helix of RAG2 is
denoted in blue. Yellow, zinc-coordinating cysteine residues;
blue, zinc-coordinating histidine residues; red spheres, zinc
atoms.
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