Evidence for more than two metallothionein isoforms in primates

Area of Science:

• Biochemistry
• Molecular Biology
• Toxicology

Background:

• Mammalian cells typically express two isoforms of metallothionein (MT).
• Metallothioneins are low molecular weight, cysteine-rich proteins involved in metal ion homeostasis and detoxification.
• Previous studies suggested a limited number of MT isoforms in mammals.

Purpose of the Study:

• To investigate the diversity of metallothionein isoforms in primate cells.
• To characterize cadmium-induced metallothioneins (Cd-MTs) in HeLa cells and rhesus monkey liver.
• To determine if more than two MT isoforms exist in primates.

Main Methods:

• Exposure of HeLa cells and rhesus monkeys to cadmium (Cd2+).
• Separation of Cd-binding proteins using gel filtration and ion-exchange chromatography.
• Identification of proteins as MTs via amino acid analysis.
• Carboxymethylation and analysis by electrophoresis under denaturing conditions.

Main Results:

• Four distinct low molecular weight Cd-binding proteins were isolated from Cd2+-exposed HeLa cells.
• Amino acid analysis and electrophoresis confirmed three of these HeLa cell proteins as distinct MT molecules.
• Analysis of hepatic MTs from Cd2+-exposed rhesus monkeys revealed five distinct isomers.
• These findings demonstrate the presence of more than two MT isoforms in primate species.

Conclusions:

• The study demonstrates the existence of at least three MT isoforms in primate HeLa cells and five in rhesus monkey liver.
• This finding expands the known diversity of metallothionein isoforms beyond the traditionally recognized two in mammals.
• Further research is needed to fully elucidate the functional significance of these multiple MT isoforms in primates.