Metallothionein in Antarctic Fish
155
from cloned colonies was sequenced on both strands by the dideoxy
method using the T7 sequencing kit (Pharmacia Biotech.). The translated
amino acid sequence reported in Fig. 2 shows a protein made of 60
residues with 20 cysteines arranged in a fashion typical of vertebrate
MTs; the homology to rat MT-2 is also shown in Fig. 2.
TberMT MDP-CQCSKS GTCNCGGSCT CTNCSCTSCK KSCCPCCPSG CTKCASGCVC KGKTCDTSCC Q
RatMT2 MDPNCSCATD GSCSCAGSCK CKQCKCTSCK KSCCSCCPVG CAKCSQGCIC KEASDKCSCC A
*** * *
* * * *** * * ***** ****.*** * * ** **.* *
***
Fig. 2. Primary amino acid sequences of T bernacchii and rat MTs.
As MT lacks well-defined secondary structure elements such as uhelices and ~-strands, it is not well-suited for comparative model building.
However, since the domains that bind heavy metals in MT are likely to be
structurally conserved, a model building based on the replacement of the
substituted amino acids in a suitable template could be allowed. Modeling
of the T bernacchii MT was performed by Swiss PDB Viewer using
ProMod Tools [23] and rat MT-2 structure as template. The threedimensional structure of T bernacchii MT is shown in Fig. 3 together
with the experimentally determined structure of rat MT-2.
A
B
Fig. 3. Comparison between the experimental three-dimensional structure of rat MT (A)
and the homology modeled T bernacchii MT (B)