Evolutionary analysis of the functional plasticity of Staphylococcus aureus C30 carotenoid synthase

The Promiscuity of Squalene Synthase-Like Enzyme: Dehydrosqualene Synthase, a Natural Squalene Hyperproducer?

Dehydrosqualene synthase (CrtM), as a squalene synthase-like enzyme from Staphylococcus aureus, can naturally utilize farnesyl diphosphate to produce dehydrosqualene (C30H48). However, no study has documented the natural production of squalene (C30H50) by CrtM. Here, based on an HPLC-Q-Orbitrap-MS/MS study, we report that the expression of crtM in vitro or in Bacillus subtilis 168 both results in the output of squalene, dehydrosqualene, and phytoene (C40H64). Notably, wild-type CrtM exhibits a significantly higher squalene yield compared to squalene synthase (SQS) from Bacillus megaterium with an approximately 2.4-fold increase. Moreover, the examination of presqualene diphosphate's stereostructures in both CrtM and SQS enzymes provides further understanding into the presence of multiple identified terpenoids. In summary, this study not only provides insights into the promiscuity demonstrated by squalene synthase-like enzymes but also highlights a new strategy of utilizing CrtM as a potential replacement for SQS in cell factories, thereby enhancing squalene production.

The sources, properties, extraction, biosynthesis, pharmacology, and application of lycopene

Lycopene is an important pigment with an alkene skeleton from Lycopersicon esculentum, which is also obtained from some red fruits and vegetables. Lycopene is used in the food field with rich functions and serves in the medical field with multiple clinical values because it has dual functions of both medicine and food. It was found that lycopene was mainly isolated by solvent extraction, ultrasonic-assisted extraction, supercritical fluid extraction, high-intensity pulsed electric field-assisted extraction, enzymatic-assisted extraction, and microwave-assisted extraction. Meanwhile, it was also obtained via 2 synthetic pathways: chemical synthesis and biosynthesis. Pharmacological studies revealed that lycopene has anti-oxidant, hypolipidemic, anti-cancer, immunity-enhancing, hepatoprotective, hypoglycemic, cardiovascular-protective, anti-inflammatory, neuroprotective, and osteoporosis-inhibiting effects. The application of lycopene mainly includes food processing, animal breeding, and medical cosmetology fields. It is hoped that this review will provide some useful information and guidance for future study and exploitation of lycopene.

Engineering the β-Carotene Metabolic Pathway of Microalgae Dunaliella To Confirm Its Carotenoid Synthesis Pattern in Comparison To Bacteria and Plants

Dunaliella salina is the most salt-tolerant eukaryote and has the highest β-carotene content, but its carotenoid synthesis pathway is still unclear, especially the synthesis of lycopene, the upstream product of β-carotene. In this study, DsGGPS, DsPSY, DsPDS, DsZISO, DsZDS, DsCRTISO, and DsLYCB genes were cloned from D. salina and expressed in Escherichia coli. A series of carotenoid engineering E. coli strains from phytoene to β-carotene were obtained. ZISO was first identified from Chlorophyta, while CRTISO was first isolated from algae. It was found that DsZISO and DsCRTISO were essential for isomerization of carotenoids in photosynthetic organisms and could not be replaced by photoisomerization, unlike some plants. DsZDS was found to have weak beta cyclization abilities, and DsLYCB was able to catalyze 7,7',9,9'-tetra-cis-lycopene to generate 7,7',9,9'-tetra-cis-β-carotene, which had not been reported before. A new carotenoid 7,7',9,9'-tetra-cis-β-carotene, the beta cyclization product of prolycopene, was discovered. Compared with the bacterial-derived carotenoid synthesis pathway, there is higher specificity and greater efficiency of the carotenoid synthesis pathway in algae. This research experimentally confirmed that the conversion of phytoene to lycopene in D. salina was similar to that of plants and different from bacteria and provided a new possibility for the metabolic engineering of β-carotene. IMPORTANCE The synthesis mode of all trans-lycopene in bacteria and plants is clear, but there are still doubts in microalgae. Dunaliella is the organism with the highest β-carotene content, and plant-type and bacterial-type enzyme genes have been found in its carotenoid metabolism pathway. In this study, the entire plant-type enzyme gene was completely cloned into Escherichia coli, and high-efficiency expression was obtained, which proved that carotenoid synthesis of algae is similar to that of plants. In bacteria, CRT can directly catalyze 4-step continuous dehydrogenation to produce all trans-lycopene. In plants, four enzymes (PDS, ZISO, ZDS, and CRTISO) are involved in this process. Although a carotenoid synthetase similar to that of bacteria has been found in algae, it does not play a major role. This research reveals the evolutionary relationship of carotenoid metabolism in bacteria, algae, and plants and is of methodologically innovative significance for molecular evolution research.

An Efficient Virus-Induced Gene Silencing System for Functional Genomics Research in Walnut (Juglans regia L.) Fruits

The Persian walnut (Juglans regia L.) is a leading source of woody oil in warm temperate regions and has high nutritional and medicinal values. It also provides both tree nuts and woody products. Nevertheless, incomplete characterization of the walnut genetic system limits the walnut gene function analysis. This study used the tobacco rattle virus (TRV) vector to construct an infectious pTRV-JrPDS recombinant clone. A co-culture inoculation method utilizing Agrobacterium was screened out from four inoculation methods and optimized to set up an efficient virus-induced gene silencing (VIGS) system for J. regia fruit. The optimized VIGS-TRV system induced complete photobleaching phenotype on the walnut fruits of four cultivars, and the JrPDS transcript levels decreased by up to 88% at 8 days post-inoculation (dpi). While those of browning-related J. regia polyphenol oxidase (PPO) genes JrPPO1 and JrPPO2 decreased by 67 and 80% at 8 dpi, respectively, accompanied by a significant reduction in fruit browning phenotype. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis screening and Western Blot showed that the PPO protein levels were significantly reduced. Moreover, a model of TRV-mediated VIGS system for inoculating J. regia fruit with efficient silence efficiency via co-culture was developed. These results indicate that the VIGS-TRV system is an efficient tool for rapid gene function analysis in J. regia fruits.

Construction of a Nonnatural C60 Carotenoid Biosynthetic Pathway

Longer-chain carotenoids have interesting physiological and electronic/photonic properties due to their extensive polyene structures. Establishing nonnatural biosynthetic pathways for longer-chain carotenoids in engineerable microorganisms will provide a platform to diversify and explore the potential of these molecules. We have previously reported the biosynthesis of nonnatural C₅₀ carotenoids by engineering a C₃₀-carotenoid backbone synthase (CrtM) from Staphylococcus aureus. In the present work, we conducted a series of experiments to engineer C₆₀ carotenoid pathways. Stepwise introduction of cavity-expanding mutations together with stabilizing mutations progressively shifted the product size specificity of CrtM toward efficient synthases for C₆₀ carotenoids. By coexpressing these CrtM variants with hexaprenyl diphosphate synthase, we observed that C₆₀-phytoene accumulated together with a small amount of C₆₅-phytoene, which is the largest carotenoid biosynthesized to date. Although these carotenoids failed to serve as a substrate for carotene desaturases, the C₂₅-half of the C₅₅-phytoene was accepted by the variant of phytoene desaturase CrtI, leading to accumulation of the largest carotenoid-based pigments. Continuing effort should further expand the scope of carotenoids, which are promising components for various biological (light-harvesting, antioxidant, and communicating) and nonbiological (photovoltaic, photonic, and field-effect transistor) systems.