Transglutaminases of the lower organisms. Across the link between life and death

Unicellular and small multicellular organisms have remarkable ability to protect themselves from environmental and physiologic changes and evolve to withstand complex patterns of life. One important mechanism by which they accomplish this is the synthesizing of rigid and inert structures around them. In general, these structures are highly stable and resistant to mechanical disruption and chemical attacks. Biochemically, they are composed of complex carbohydrates, such as chitin, and heavily crosslinked protein aggregates. Transglutaminases (TGases) are a family of enzymes that catelyze protein crosslink reactions by establishing E-(γ-glutamyl)lysine bonds that are resistant to reducing agents, detergents, and chaotropic agents. Therefore, it is likely that protective structures synthesized by the microorganisms under certain conditions involve active participation of TGases. In this review, we briefly describe the current knowledge of non-mammalian TGases and their possible role in growth, development, and survival of these small organisms. Special reference is made to nematode and bacterial TGases, since they are the most well characterized and studied enzymes among non-mammalian TGasss.