Biology Reference
In-Depth Information
F
IG
. 4. Crystal structures of the dimerization domain of MutL. The structures of
B. subtilis
MutL (residues 433-627),
N. gonorrhoeae
MutL (residues 463-656), and
E. coli
MutL (residues
432-615) are shown as ribbon diagrams with the secondary structure motifs labeled. The conserved
motifs defining the endonuclease site are highlighted in purple and the
b
-binding motifs are colored
orange and labeled. The Zn
2
þ
metal ions found in the structure of
B. subtilis
MutL are shown as
teal spheres. Helices are labeled with letters (A-F) and strands with consecutive numbers from the
N to the C terminus.
Despite the low sequence conservation among the dimerization regions of
MutL proteins from different organisms, the structures available reveal a
common topology (
Fig. 4
). Even helix
a
, which only in certain MutL homo-
logs encompasses the endonuclease motif, is structurally conserved. However,
the orientation of this helix is different depending on whether the protein
contains the conserved endonuclease motif (like
B. subtilis
and
N. gonorrhoeae
MutL) or not (like
E. coli
MutL). In MutL proteins containing the conserved
endonuclease motif, helix
a
Α
undergoes a rigid-body movement that changes
Α
