STARD6 is a steroidogenic acute regulatory protein-related lipid transfer (START) domain protein that exhibits testis-specific expression and cholesterol-binding activity. The protein is expressed exclusively in male germ cells, specifically during the maturation stages of round and elongated spermatids in adult testis 1. STARD6 demonstrates steroidogenic activity equal to STARD1, the prototype cholesterol transport protein, and can stimulate steroidogenesis in mitochondrial assays 2. The protein contains a conserved START domain forming an α-helix/β-grip fold with an internal hydrophobic cavity that specifically binds cholesterol and testosterone 3. Structural studies reveal that STARD6 undergoes conformational changes involving the Ω1 loop and C-terminal helix on microsecond-millisecond timescales, allowing ligand entry into the binding site 3. Unlike other START domain proteins, STARD6 exhibits molten globule behavior similar to STARD1 and shows strong membrane association properties 2. In human ovarian tissues, STARD6 transcripts are present but appear to be splice variants that do not produce detectable protein 4. The protein's testis-specific expression pattern and steroidogenic capabilities suggest a specialized role in cholesterol transport during male germ cell development and steroid hormone synthesis.