The molecular chaperone system and other anti-stress mechanisms in archaea

This article presents a brief review of stressors, their cellular and intra cellular targets, stress proteins, molecular chaperones, and other anti-str ess mechanisms. New data are reported on cochaperones and multicellular str uctures in archaea. The molecular chaperoning systems of bacteria and eukar yotes have been studied for many years and are relatively well known in ter ms of their components and mechanisms of action, although many details rema in to be elucidated and almost certainly other components will be discovere d in the future. By comparison, the molecular chaperoning system of archaea is still unexplored. Since archaea have some molecular genetic and physiol ogic features similar to those of bacteria and some resembling those of euk aryotes, extrapolation from what is known of organisms from these two phylo genetic domains to archaeal species is unwarranted. For example, the compon ents of the molecular chaperone machine, Hsp70( DnaK), Hsp40( DnaJ), and Gr pE, in the archaeal species that have it, are closely related to bacterial counterparts, whereas the archaeal chaperonins are like the eukaryotic equi valents. Furthermore, many archaeal species lack the chaperone machine, in contrast to bacteria and eukaryotes that have it without any known exceptio n. A search for the cochaperones trigger factor, Hop, Hip, BAG-1, and NAC i n archaeal genomes demonstrated no conserved equivalents, but two families of archaeal molecules were identified that might be related to NAC and Hop, respectively. Multicellular structures with a single species such as packe t and lamina are formed by Methanosarcina species, among which the best stu died is M. mazeii. Multispecies multicellular structures are formed by a va riety of archaeal organisms, which are either flat (biofilm) or globular (g ranule) and constitute a functional association or consortium. Details of m orphology, formation, and internal organization are described for represent ative examples of multicellular structures. These may be seen as the result of primitive histogenesis reflecting primeval mechanisms of differentiatio n-development that might have evolved driven by environmental stressors. Ce lls in these complex threedimensional arrangements are not only positioned so they can interact with each other for more efficient functioning as in a tissue or organ, but are also protected from stressors. Single cells lacki ng the protective shield of other cells packed together with intercellular connective material, which is typical of multicellular structures, are dire ctly exposed to environmental stressors and, thus, are at a disadvantage fr om the evolutionary standpoint. It seems reasonable to argue that different iation-development leading to histogenesis might have arisen in primeval ti mes as a consequence of the harsh conditions that primitive life forms had to endure, and that the ability to form tissue-like structures was a primar y characteristic that ensured positive selection.