Carbohydrate Metabolism in Archaea: Current Insights into Unusual Enzymes and Pathways and Their Regulation

<jats:title>SUMMARY</jats:title><jats:p>The metabolism of<jats:named-content content-type="genus-species">Archaea</jats:named-content>, the third domain of life, resembles in its complexity those of<jats:named-content content-type="genus-species">Bacteria</jats:named-content>and lower<jats:named-content content-type="genus-species">Eukarya</jats:named-content>. However, this metabolic complexity in<jats:named-content content-type="genus-species">Archaea</jats:named-content>is accompanied by the absence of many “classical” pathways, particularly in central carbohydrate metabolism. Instead,<jats:named-content content-type="genus-species">Archaea</jats:named-content>are characterized by the presence of unique, modified variants of classical pathways such as the Embden-Meyerhof-Parnas (EMP) pathway and the Entner-Doudoroff (ED) pathway. The pentose phosphate pathway is only partly present (if at all), and pentose degradation also significantly differs from that known for bacterial model organisms. These modifications are accompanied by the invention of “new,” unusual enzymes which cause fundamental consequences for the underlying regulatory principles, and classical allosteric regulation sites well established in<jats:named-content content-type="genus-species">Bacteria</jats:named-content>and<jats:named-content content-type="genus-species">Eukarya</jats:named-content>are lost. The aim of this review is to present the current understanding of central carbohydrate metabolic pathways and their regulation in<jats:named-content content-type="genus-species">Archaea</jats:named-content>. In order to give an overview of their complexity, pathway modifications are discussed with respect to unusual archaeal biocatalysts, their structural and mechanistic characteristics, and their regulatory properties in comparison to their classic counterparts from<jats:named-content content-type="genus-species">Bacteria</jats:named-content>and<jats:named-content content-type="genus-species">Eukarya</jats:named-content>. Furthermore, an overview focusing on hexose metabolic, i.e., glycolytic as well as gluconeogenic, pathways identified in archaeal model organisms is given. Their energy gain is discussed, and new insights into different levels of regulation that have been observed so far, including the transcript and protein levels (e.g., gene regulation, known transcription regulators, and posttranslational modification via reversible protein phosphorylation), are presented.</jats:p>