Structural comparisons of representative treble clef fingers.
Structural diagrams of the treble clef of the steroid hormone
"estrogen" receptor DNA-binding domain showing both zinc-binding sites
(1hcq, chain A, residues 3-36 and 39-71), prolyl-tRNA synthetase
(1hc7, chain A, residues 454-477; 418-440) and the RPB10 protein
from RNA polymerase II (1i3q, chain J, residues 3-54) are shown to
illustrate the wide range of variations in the structure of the treble
clef finger. The N-terminal site of 1hcq is a typical treble clef motif.
The C-terminal site (below), reoriented for clarity, lacks the β-hairpin
shown in yellow for the N-terminal treble clef and has a distorted knuckle
(red). This zinc-binding region shows some resemblance to other treble
clef fingers in the placement of the ligands for zinc-binding. However,
the knuckle, which contributes the other two ligands in treble clef fingers,
is significantly different and does not align structurally with those in other fingers.
PSI-BLAST alignment of representative nuclear receptor sequences is also shown.
The sequences included in the alignment are: the nuclear factor NHR-63 (gi 10198059),
peroxisome proliferator activated receptor (gi 13432234), NHR-18 (gi 11359799),
retenoid X receptor (2nll), estrogen receptor (1hcq), tailless protein (TLL_DROME gi 135913),
FTZ-F1 (gi 12239372), dissatisfaction (gi 4160012), NHR-67 (gi 3874154)
and NHR-2 (gi 7511505).