The first genetic engineered system for ovothiol biosynthesis in diatoms reveals a mitochondrial localization for the sulfoxide synthase OvoA

Abstract

Diatoms represent one of the most abundant groups of microalgae in the ocean and are responsible for approximately 20% of photosynthetically fixed CO 2 on Earth. Due to their complex evolutionary history and ability to adapt to different environments, diatoms are endowed with striking molecular biodiversity and unique metabolic activities. Their high growth rate and the possibility to optimize their biomass make them very promising ‘biofactories’ for biotechnological applications. Among bioactive compounds, diatoms can produce ovothiols, histidine-derivatives, endowed with unique antioxidant and anti-inflammatory properties, and occurring in many marine invertebrates, bacteria and pathogenic protozoa. However, the functional role of ovothiols biosynthesis in organisms remains almost unexplored. In this work, we have characterized the thiol fraction of Phaeodactylum tricornutum , providing the first evidence of the presence of ovothiol B in pennate diatoms. We have used P. tricornutum to overexpress the 5-histidylcysteine sulfoxide synthase ovoA , the gene encoding the key enzyme involved in ovothiol biosynthesis and we have discovered that OvoA localizes in the mitochondria, a finding that uncovers new concepts in cellular redox biochemistry. We have also obtained engineered biolistic clones that can produce higher amount of ovothiol B compared to wild-type cells, suggesting a new strategy for the eco-sustainable production of these molecules.

Insights on the UV-Screening Potential of Marine-Inspired Thiol Compounds

“…These features indicate that ovothiols may display UVA-protecting properties, resembling the behaviour of MAAs, which are currently considered the strongest UVA-absorbing compounds in nature [11,12,35], due to their ability to absorb light both in the UVA (315-400 nm) and UVB (280-315 nm) range and to their high molar extinction coefficient [11,12]. Since obtaining ovothiols from the most abundant natural source e.g., sea urchin eggs [34], cannot be considered an eco-sustainable strategy, recent efforts have been devoted to developing engineered microorganisms aimed at their biosynthesis [17] and to screening the chemical and biological properties of synthetic derivatives to compare their activities with natural counterparts for further industrial development.…”

“…This work aimed to characterize the UV-screening properties of novel marine-inspired compounds to develop natural-based sunscreens and personal-care products that could be both safer for human use and more environmentally friendly. Our attention focused on sulfur-containing histidine compounds, named ovothiols, known to be produced by several marine invertebrates, like the sea urchin Paracentrotus lividus, bacteria (i.e., Erwinia tasmaniensis), and microalgae, especially diatoms belonging to stramenopiles, like Skeletonema marinoi and Phaeodactylum tricornutum [13][14][15][16][17]. These compounds occur in three differently methylated forms (A, B, and C) and are characterized by unique redox properties suggestive of numerous cellular functions [14,[16][17][18][19].…”

“…Our attention focused on sulfur-containing histidine compounds, named ovothiols, known to be produced by several marine invertebrates, like the sea urchin Paracentrotus lividus, bacteria (i.e., Erwinia tasmaniensis), and microalgae, especially diatoms belonging to stramenopiles, like Skeletonema marinoi and Phaeodactylum tricornutum [13][14][15][16][17]. These compounds occur in three differently methylated forms (A, B, and C) and are characterized by unique redox properties suggestive of numerous cellular functions [14,[16][17][18][19]. They possess unusual antioxidant properties due to the peculiar position of the sulfhydryl group on the imidazole ring of histidine, which confers ovothiols remarkable reactivity towards reactive oxygen species (ROS) [14,[20][21][22].…”

Microalgae Produce Antioxidant Molecules with Potential Preventive Effects on Mitochondrial Functions and Skeletal Muscular Oxidative Stress

“…Among them, resveratrol showed a positive role in AREs during physical activity [87,88], and ergothioneine, a sulfated derivate of histidine, was shown to stimulate the gene Nrf2, an important regulator of the ARE [89]. Ergothioneine is the only sulfur-derivate of histidine to be reported to have any effect on muscle, but it can be noticed that ovothiols, other derivates of histidine produced by microalgae [90,91] have also been reported to regulate Nrf2 into keratinocytes, inducing a dermo-protective effect [92].…”

The tonoplast localized protein PtNPF1 participates in the regulation of nitrogen response in diatoms

“…The two constructs were generated using the Gibson assembly method (Gibson et al, 2009(Gibson et al, , 2010 following the manufacturer's instructions. For PtNPF1-YFP, the PtLhcf2pPtovoAyfp plasmid (Russo et al, 2023), containing the Light Harvesting Complex protein family F2 promoter (Lhcf2p), was used as backbone, for PtGFP-NPF1, the PmH4pH4N-GFP plasmid (Sabatino et al, 2015), containing the Pseudo-nitzschia multistriata histone H4 promoter (PmH4p), was used as backbone.…”