Abstract
Heavy metals are found in all living organisms where, as indispensable microelements (e.g. zinc, iron, copper), are involved in endless metabolic processes. However, living organisms are also at a risk of exposure to highly toxic metals, including cadmium or lead, which do not play any physiological role. Among multiple mechanisms associated with the maintenance of micronutrient homeostasis and detoxification of unwanted metals, there is a family of low-molecular-weight, cysteine-rich proteins, able to chelate multiple metal ions i.e. the metallothioneins (MTs). They are widely distributed among Eucaryota, however, they have also been found in some limited Procaryota, including cyanobacteria, pseudomonads and mycobacteria. These bacterial MTs differ in terms of primary structure, the number and type of metal ions they bind, as well as with regard to their physiological functions. The expression of bacterial MTs is regulated by metals via metalosensors. MTs from cyanobacteria seem to be involved in zinc homeostasis, while in Pseudomonas they are linked to cadmium detoxification. In Mycobacterium, MTs bind copper ions and may play a pivotal role in the virulence of these bacteria. The presence of MTs in other groups of bacteria remains questionable. Problems with identification of new bacterial MTs are mainly associated with low level of homology between MT amino acid sequences of different bacterial groups. Further research is needed to evaluate the physiological functions of metallothioneins in Procaryota.
1. Introduction. 2. The history of discoveries of bacterial metallothioneins. 3. Structure and metal-binding properties of bacterial MTs. 4. Functions of bacterial metallothioneins. 5. Regulation of metallothionein gene expression. 6. Presence of metallothioneins in bacteria. 7. Summary
1. Wstęp. 2. Historia odkryć metalotionein u bakterii. 3. Budowa i sposób wiązania jonów metali ciężkich przez bakteryjne MT. 4. Funkcje metalotionein bakteryjnych. 5. Regulacja ekspresji bakteryjnych metalotionein. 6. Obecność metalotionein u bakterii. 7. Podsumowanie