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This review discusses the intriguing yet controversial concept of metabolons, focusing on the malate dehydrogenase-citrate synthase (MDH-CISY) metabolon as a model. Metabolons are multienzyme complexes composed of enzymes that catalyze sequential reactions in metabolic pathways. Metabolons have been proposed to enhance metabolic pathway efficiency by facilitating substrate channeling. However, there is skepticism about the presence of metabolons and their functionality in physiological conditions in vivo. We address the skepticism by reviewing compelling evidence supporting the existence of the MDH-CISY metabolon and highlighting its potential functions in cellular metabolism. The electrostatic interaction between MDH and CISY and the intermediate oxaloacetate, channeled within the metabolon, has been demonstrated using various experimental techniques, including protein–protein interaction assays, isotope dilution studies, and enzyme coupling assays. Regardless of the wealth of in vitro evidence, further validation is required to elucidate the functionality of MDH-CISY metabolons in living systems using advanced structural and spatial analysis techniques. 

The COVID-19 outbreak has had a significant impact on higher education worldwide. In-person courses had to be quickly transited to online, including lab courses embedded with Course-based Undergraduate Research Experiences (CUREs). In response to this challenge, we successfully converted a fully in-person biochemistry lab that integrated with a 6-week modular CURE (mCURE) into a hybrid CURE (hCURE) in Fall 2020, with support from the Malate dehydrogenase CUREs Community. The hCURE was structured to have in-person labs and online activities arranged on an alternating weekly basis, so that only half of the regular class size of students attended the hands-on labs at any given time to maintain proper social distancing. To evaluate the efficacy of the hCURE, student science self-efficacy and conceptual understanding of protein structure–function relationships were measured using pre-course and post-course surveys and tests, respectively. Our data showed a significant increase in student science self-efficacy and conceptual knowledge test scores. Furthermore, we compared the pre-lab quiz scores that assessed various biochemical concepts and skills across three different semesters, Fall 2019 with a fully in-person mCURE before the pandemic, Fall 2020 with the hCURE implemented during the pandemic, and Fall 2021 when the lab returned to the fully in-person mCURE following the pandemic. A significant decline in quiz scores from Fall 2019 to Fall 2020, and an even further decline from Fall 2019 to Fall 2021 were observed, suggesting that apart from the impact of course modality, the pandemic may have exerted a lasting adverse effect on student learning. 

Selective autolysosomal degradation of damaged mitochondria, also called mitophagy, is an indispensable process for maintaining integrity and homeostasis of mitochondria. One well-established mechanism mediating selective removal of mitochondria under relatively mild mitochondria-depolarizing stress is PINK1-Parkin-mediated or ubiquitin-dependent mitophagy. However, additional mechanisms such as LC3-mediated or ubiquitin-independent mitophagy induction by heavy environmental stress exist and remain poorly understood. The present study unravels a novel role of stress-inducible protein Sestrin2 in degradation of mitochondria damaged by transition metal stress. By utilizing proteomic methods and studies in cell culture and rodent models, we identify autophagy kinase ULK1-mediated phosphorylation sites of Sestrin2 and demonstrate Sestrin2 association with mitochondria adaptor proteins in HEK293 cells. We show that Ser-73 and Ser-254 residues of Sestrin2 are phosphorylated by ULK1, and a pool of Sestrin2 is strongly associated with mitochondrial ATP5A in response to Cu-induced oxidative stress. Subsequently, this interaction promotes association with LC3-coated autolysosomes to induce degradation of mitochondria damaged by Cu-induced ROS. Treatment of cells with antioxidants or a Cu chelator significantly reduces Sestrin2 association with mitochondria. These results highlight the ULK1-Sestrin2 pathway as a novel stress-sensing mechanism that can rapidly induce autophagic degradation of mitochondria under severe heavy metal stress.