Hexokinase 1 forms rings that constrict mitochondria during energy stress

Summary Metabolic enzymes can adapt during energy stress, but the precise mechanisms and consequences of these adaptations remain understudied. Here, we discovered that hexokinase 1 (HK1), a key glycolytic enzyme, clusters into ring-like structures around mitochondria during energy stress. These HK1-rings constrict mitochondria at contact sites with the endoplasmic reticulum (ER) and prevent mitochondrial fission by displacing the dynamin-related protein 1 (Drp1) from mitochondrial constriction sites. Mechanistically, we identified that the lack of ATP and glucose-6-phosphate (G6P) promotes the clustering of HK1. Moreover, we found several mutations that are critical for the formation of HK1-rings. Utilizing these mutations, we could show that HK1-rings keep mitochondria connected and rewire cellular metabolism during energy stress. Our findings highlight that HK1 is a robust energy stress sensor that regulates the shape, connectivity and metabolic activity of mitochondria. Thus, the formation of HK1-rings may affect mitochondrial function in energy stress-related pathologies.