Moonlighting proteins: putting the spotlight on enzymes

Aromatic Amino Acids: Exploring Microalgae as a Potential Biofactory

In recent times, microalgae have emerged as powerful hosts for biotechnological applications, ranging from the production of lipids and specialized metabolites (SMs) of pharmaceutical interest to biofuels, nutraceutical supplements, and more. SM synthesis through bioengineered pathways relies on the availability of aromatic amino acids (AAAs) as an essential precursor. AAAs, phenylalanine, tyrosine, and tryptophan are also the building blocks of proteins, maintaining the structural and functional integrity of cells. Hence, they are crucial intermediates linking the primary and specialized metabolism. The biosynthesis pathway of AAAs in microbes and plants has been studied for decades, but not much is known about microalgae. The allosteric control present in this pathway has been targeted for metabolic engineering in microbes. This review focuses on the biosynthesis of AAAs in eukaryotic microalgae and engineering techniques for enhanced production. All the putative genes involved in AAA pathways in the model microalgae Chlamydomonas reinhardtii and Phaeodactylum tricornutum are listed in this review.

Moonlighting Proteins: The Case of the Hexokinases

Moonlighting proteins are defined as proteins with two or more functions that are unrelated and independent to each other, so that inactivation of one of them should not affect the second one and vice versa. Intriguingly, all the glycolytic enzymes are described as moonlighting proteins in some organisms. Hexokinase (HXK) is a critical enzyme in the glycolytic pathway and displays a wide range of functions in different organisms such as fungi, parasites, mammals, and plants. This review discusses HXKs moonlighting functions in depth since they have a profound impact on the responses to nutritional, environmental, and disease challenges. HXKs’ activities can be as diverse as performing metabolic activities, as a gene repressor complexing with other proteins, as protein kinase, as immune receptor and regulating processes like autophagy, programmed cell death or immune system responses. However, most of those functions are particular for some organisms while the most common moonlighting HXK function in several kingdoms is being a glucose sensor. In this review, we also analyze how different regulation mechanisms cause HXK to change its subcellular localization, oligomeric or conformational state, the response to substrate and product concentration, and its interactions with membrane, proteins, or RNA, all of which might impact the HXK moonlighting functions.

Transcriptome analyses reveal key genes involved in skin color changes of 'Xinlimei' radish taproot

The color of radish (Raphanus sativus) taproot skin is an important visual quality. 'Xinlimei' radish is a red-fleshed cultivar with skin that changes color from red to white and finally to green at the mature stage, and appearance quality is strongly affected if the red color does not fade completely on a single taproot or simultaneously among different taproots. In the present study, anthocyanin and chlorophyll contents and the transcriptome of radish taproot skin at three distinct coloration stages were analyzed to explore the mechanism of color changes. The results showed that decreased anthocyanin and increased chlorophyll contents correlated with the color-fading process. Kyoto Encyclopedia of Genes and Genomes enrichment analysis of differentially expressed genes indicated that anthocyanin and chlorophyll metabolism pathways play important roles in color changes. In red color-fading process, the expression levels of anthocyanin biosynthetic genes (except PAL and C4H), a transport gene (RsTT19), and two anthocyanin biosynthesis transcription factors (TFs), RsMYB1 and RsTT8, were significantly downregulated, whereas peroxidase-encoding genes were significantly upregulated. In the skin-greening process, expression of most chlorophyll biosynthetic genes and two TFs (RsGLK1 and RsGLK2) that likely positively regulate chlorophyll biosynthesis was significantly upregulated. Thus, changes in the expression of these genes may be responsible for the color changes that occur in 'Xinlimei' taproot skin. This is the first report on the roles of chlorophyll metabolism genes and their dynamic relationship with anthocyanin metabolism genes in radish. The findings provide valuable information and theoretical guidelines for improving the appearance quality of 'Xinlimei' radish taproots.