Tracing the tail of ubiquinone in mitochondrial complex I

► Ubiquinone interactions of complex I were analyzed by site-directed mutagenesis. ► Five ubiquinone derivatives with different tails were used for functional analysis. ► The isoprenoid tail structure is critical for access to the ubiquinone active site. ► A methionine rich domain acts as access gate for the hydrophobic ubiquinone tail.