Ferroptosis is a form of regulated cell death with roles in degenerative diseases and cancer. Ferroptosis is driven by excessive iron-dependent peroxidation of membrane phospholipids, especially those containing the polyunsaturated fatty acid arachidonic acid. Here, we reveal that an understudied Golgi membrane scaffold protein, MMD, promotes susceptibility to ferroptosis in ovarian and renal carcinoma cells. Upregulation of MMD correlates with sensitization to ferroptosis upon monocyte-to-macrophage differentiation. Mechanistically, MMD interacts with ACSL4 and MBOAT7, two enzymes that catalyze consecutive reactions in the biosynthesis of phosphatidylinositol (PI) containing arachidonic acid. MMD increases cellular levels of arachidonoyl-phospholipids and heightens susceptibility to ferroptosis in an ACSL4- and MBOAT7-dependent manner. We propose that MMD potentiates the synthesis of arachidonoyl-PI by bridging ACSL4 with MBOAT7. This molecular mechanism not only clarifies the biochemical underpinnings of ferroptosis susceptibility, with potential therapeutic implications, but also contributes to our understanding of the regulation of cellular lipid metabolism.
SARS-CoV-2 virus spike (S) protein is an envelope protein responsible for binding to the ACE2 receptor, driving subsequent entry into host cells. The existence of multiple disulfide bonds in the S protein makes it potentially susceptible to reductive cleavage. Using a tri-part split luciferase-based binding assay, we evaluated the impacts of chemical reduction on S proteins from different virus variants and found that those from the Omicron family are highly vulnerable to reduction. Through manipulation of different Omicron mutations, we found that alterations in the receptor binding module (RBM) are the major determinants of this vulnerability. Specifically we discovered that Omicron mutations facilitate the cleavage of C480-C488 and C379-C432 disulfides, which consequently impairs binding activity and protein stability. The vulnerability of Omicron S proteins suggests a mechanism that can be harnessed to treat specific SARS-CoV-2 strains.
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