The specific molecular architecture of plant 3-hydroxy-3-methylglutaryl-CoA lyase

Biological and metabolic effects of the association between the microalga Galdieria sulphuraria and the fungus Penicillium citrinum

Contamination of microalgae cultures can reduce their productivity and affect the quality of biomass and valuable bioproducts. In this article, after having isolated and identified for the first time the filamentous fungus Penicillium citrinum from heterotrophic cultures of the red polyextremophilic microalga Galdieria sulphuraria, we investigated the biological and metabolic significance of this alga-fungus association. In the same medium, both organisms grow better in each other's presence than separately. Both cell density and cell size of G. sulphuraria increase in co-cultures compared to pure alga cultures. In co-cultures, despite very severe growth conditions, the load of P. citrinum increases compared to pure fungus cultures. Optical microscope images have shown physical contact between cells of P. citrinum hyphae and G. sulphuraria which, however, retain their morphology and cell wall intact. GC-MS-based metabolomics analysis of metabolites excreted in the culture medium shows that pure cultures of the fungus and alga and co-cultures of alga plus fungus can be easily differentiated based on their metabolic products. Indeed, a richer assortment of extracellular metabolites (comprising both products of primary and secondary metabolism) is a distinct feature of co-cultures compared to both pure alga and pure fungus cultures.

More Than One HMG-CoA Lyase: The Classical Mitochondrial Enzyme Plus the Peroxisomal and the Cytosolic Ones

There are three human enzymes with HMG-CoA lyase activity that are able to synthesize ketone bodies in different subcellular compartments. The mitochondrial HMG-CoA lyase was the first to be described, and catalyzes the cleavage of 3-hydroxy-3-methylglutaryl CoA to acetoacetate and acetyl-CoA, the common final step in ketogenesis and leucine catabolism. This protein is mainly expressed in the liver and its function is metabolic, since it produces ketone bodies as energetic fuels when glucose levels are low. Another isoform is encoded by the same gene for the mitochondrial HMG-CoA lyase (HMGCL), but it is located in peroxisomes. The last HMG-CoA lyase to be described is encoded by a different gene, HMGCLL1, and is located in the cytosolic side of the endoplasmic reticulum membrane. Some activity assays and tissue distribution of this enzyme have shown the brain and lung as key tissues for studying its function. Although the roles of the peroxisomal and cytosolic HMG-CoA lyases remain unknown, recent studies highlight the role of ketone bodies in metabolic remodeling, homeostasis, and signaling, providing new insights into the molecular and cellular function of these enzymes.