Macoilin, also known as TMEM57 (transmembrane protein 57), is a 664 amino acid multi-pass membrane protein that belongs to the macoilin family. It is expressed in lung, testis, pancreas, spleen, liver, brain, thymus, kidney and muscle tissue. Human Macoilin is thought to play a role in axonal traffic or signaling events and shares 99% sequence homology with its mouse counterpart, suggesting a conserved function between species.