Metallothionein (MT) is characterized by its high content in cysteine residues (30%) and lack of aromatic
amino acids and histidines. Metallothionein also lacks disulfide bonds, thus is capable of binding a large number
of metal ions (7 in the case of mammalian MT). The first function attributed to MT was metal detoxification (Hg2+, Cd2+),
other possible roles are metallo-regulator of Zn2+ and Cu+ as well as the detoxification of reactive oxygen species
and metabolism of metallodrugs and alkylating agents [1]. Human and mammalian MTs bind 7 Zni2+ or Cd 2+ ions via 20 cysteine residues, which are distributed in two independent
and kinetically and thermodynamically different clusters, Cd4S11 and Cd3S9, located in the a-
and b-domains of the protein,
respectively. Crustacean MTs contain only 18 cysteines and 6 Cd2+ (Figure 1) which give rise to two b domains containing a Cd3S9
cluster each, referred to as bN and bC.
Previous structural studies carried out in both species by 2D-NMR techniques show
that the Cd-cysteine coordination and therefore the folding differs among these Cd3S9 clusters in the
b-domains of crustacean
and mammalian MTs [2,3]. It was also shown that the reactions of lobster
MT with thiol reagents such as DTNB (5,5'-dithio-2,2'dinitro
benzoic acid) or DTP (2-2'-dithiopyridine) were also biphasic but more rapid than in the case of the mammalian MT reactions. Thus,
the difference in cluster structure as reason for the biphasic kinetic was ruled out. It was proposed then, that the kinetic
and thermodynamic reactivity of the MT domains is related to the detailed folding of the peptides around their clusters.
To analyze structure-function relationships among these domains, in this poster we describe the 3D-structure of the chemically
synthesized isolated native lobster b domains as determined by 2D-NMR spectroscopy and their reactivity toward DTNB.
Converted to HTML by F. Holger Försterling March 2001
