TOMM20 (Translocase of Outer Mitochondrial Membrane 20) is a ~20 kDa receptor subunit of the TOM complex embedded in the outer mitochondrial membrane; together with TOMM22 it forms the initial binding site that recognizes N-terminal matrix-targeting sequences on cytosol-synthesized pre-proteins and threads them through the TOMM40 channel into mitochondria, thereby governing mitochondrial biogenesis and bioenergetics, while also moonlighting as a mitophagy adaptor via PINK1, a regulator of apoptosis through BCL2/BAX, and a chaperone-like stabilizer of the androgen receptor in prostate cancer, making it a widely used marker for mitochondrial mass and a potential biomarker for diseases such as Parkinson’s and cancer .