In molecular biology, the auxin binding protein family is a family of proteins which bind auxin.[1] They are located in the lumen of the endoplasmic reticulum (ER). The primary structure of these proteins contains an N-terminalhydrophobic leader sequence of 30-40 amino acids, which could represent a signal for translocation of the protein to the ER.[2][3] The mature protein comprises around 165 residues, and contains a number of potential N-glycosylation sites. In vitrotransport studies have demonstrated co-translational glycosylation.[3] Retention within the lumen of the ER correlates with an additional signal located at the C terminus, represented by the sequence Lys-Asp-Glu-Leu, known to be responsible for preventing secretion of proteins from the lumen of the ER in eukaryoticcells.[2][3]