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Engineering metallobiocatalysts is a promising approach to addressing challenges in energy-relevant electrocatalysis and photocatalysis. The design freedom provided by semisynthetic and fully synthetic approaches to catalyst design allows researchers to demonstrate how structural modifications can improve selectivity and activity of biocatalysts. Furthermore, the provision of a superstructure in many metallobiocatalysts facilitates active-site microenvironment engineering. Recurring themes include the role of the biomolecular scaffold in enhancing reactivity in water and catalyst robustness, the impact of the outer sphere on reactivity, and the importance of tuning system components in full system optimization. In this perspective, recent strategies to design and modify novel biocatalysts, understand proton and electron transfer mechanisms, and tune system activity by modifying catalysts and system conditions are highlighted within the field of energy-related catalysis. Opportunities in this field include developing robust structure-function relationships to support approaches to engineering second-sphere interactions and identifying ways to enhance biocatalyst activity over time. 

ABSTRACT We report on the discovery and validation of a two-planet system around a bright (V  = 8.85 mag) early G dwarf (1.43  R⊙, 1.15  M⊙, TOI 2319) using data from NASA’s Transiting Exoplanet Survey Satellite (TESS). Three transit events from two planets were detected by citizen scientists in the month-long TESS light curve (sector 25), as part of the Planet Hunters TESS project. Modelling of the transits yields an orbital period of $$11.6264 _{ - 0.0025 } ^ { + 0.0022 }$$ d and radius of $$3.41 _{ - 0.12 } ^ { + 0.14 }$$ R⊕ for the inner planet, and a period in the range 19.26–35 d and a radius of $$5.83 _{ - 0.14 } ^ { + 0.14 }$$ R⊕ for the outer planet, which was only seen to transit once. Each signal was independently statistically validated, taking into consideration the TESS light curve as well as the ground-based spectroscopic follow-up observations. Radial velocities from HARPS-N and EXPRES yield a tentative detection of planet b, whose mass we estimate to be $$11.56 _{ - 6.14 } ^ { + 6.58 }$$ M⊕, and allow us to place an upper limit of 27.5 M⊕ (99 per cent confidence) on the mass of planet c. Due to the brightness of the host star and the strong likelihood of an extended H/He atmosphere on both planets, this system offers excellent prospects for atmospheric characterization and comparative planetology.