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Category: Microbial Genetics and Molecular Biology; Environmental Microbiology
Sensing, Signal Transduction, and Posttranslational Modification, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815516/9781555813918_Chap11-1.gif /docserver/preview/fulltext/10.1128/9781555815516/9781555813918_Chap11-2.gifAbstract:
This chapter focuses on other modalities of signal transduction, including intracellular second messengers, feedback regulation, and posttranslational modifications such as the phosphorylation-dephosphorylation of proteins. Empirical studies of archaeal-archaeal and archaeal-bacterial communication have been few in number and preliminary in nature. Inspection of archaeal genomes has revealed them to be devoid of homologs of the prototypic bacterial quorum-sensing proteins LuxS and LuxR. Two-component systems differ in several fundamental respects from protein-serine/threonine/tyrosine phosphorylation cascades. First, autophosohorylation is the predominant mechanism of phosphorylation in the two-component system, whereas protein-serine/threonine/tyrosine phosphorylation cascades rely primarily on phosphotransfer reactions catalyzed by protein kinases that are distinct from the phosphoacceptor protein. Second, the chemical nature of the phosphoryl moieties formed during two-component signaling differs significantly from that of protein-serine/threonine/tyrosine phosphorylation. Posttranslational modifications have discussed and demonstrated, at least in some instances, to modulate the function of one or more target proteins from the Archaea or other organisms. It is widely presumed that (poly)ADP-ribosylation regulates the functional properties of proteins, as is the case with other covalent modifications such as protein phosphorylation-dephosphorylation. Given that the members of the bacterial domain have been the subject of decades of intensive study, it appears highly likely that the Archaea will not only be found to contain new sensor-response mechanisms and molecules, but that they will provide new insights into this vital process in other organisms as well.
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Environmental variables and internal cues known or likely to be monitored by members of the Archaea.
Basic elements of biological sensor-response pathways. (A) Hypothetical multistep signal transduction pathway in which an external signal (open diamond) interacts with a transmembrane receptor complex to activate a target protein. The sensor-response pathway comprises two steps. In the first, the transmission domain of the receptor complex produces a second messenger (filled circle) that, in turn, serves as an allosteric activator for a second transmission domain (hatched circle) that catalyzes the covalent modification (open triangle) of the target (open quadrilateral). In this example, binding of the allosteric ligand and covalent modification both activate their respective target proteins by altering their conformation. (B) Hypothetical multistep biosynthetic pathway that is subject to feedback inhibition by one of the products of the final enzyme in the pathway (filled diamond). In this case, the indicator metabolite binds to and allosterically activates a sensor-transmitter fusion protein that subsequently binds to and inhibits the activity of the first enzyme in the pathway (target). The second and third enzymes in the pathway are denoted by diagonal hatching and cross hatching, respectively. See Table 1 for definitions of terms used.
Phosphorylation of phosphohexosemutase from S. solfataricus. Ser-309 on the phosphohexosemutase inhibits catalysis by electrosterically interfering with the binding of substrate phosphohexoses.
Examples of typical architectures of two-component signal transduction cascades. Shown are schematic representations of three hypothetical two-component signal transduction cascades. For each example, an external signal (open diamond) activates a histidine kinase (hatched oval) by binding to its transmembrane receptor domain (open pentagon). Response regulator domains are represented as diagonally striped rectangles. Output domains (filled circles and filled hexagons); Hpt domains (open triangles); phosphoryl transfer events (hatched arrows); conserved histidine (H) and conserved aspartate (D) residues within each two-component domain. A basic two-component signaling cascade (left); an extended two-component cascade employing a hybrid histidine kinase, i.e., one that is fused to a response regulator domain, and phosphoryl shuttle via an Hpt domain (middle); a branched two-component cascade whose right-hand branch includes an response regulator domain-Hpt domain fusion protein that serves as a phosphoryl group shuttle bridging the histidine kinase to a downstream target response regulator protein (right).
Redox regulation of coenzyme F390 metabolism in M. thermautotrophicus. Enzyme names are italicized. Events that stimulate (plus sign) or inhibit (minus sign) enzymatic activity; cysteine sulfhydryl groups (SH); cystine disulfides (S—S).