Transmembrane protein 57, also known as macoilin, is a 664-amino acid protein. Expression was high in testis, lung, spleen, and pancreas, intermediate in brain, thymus, and liver, and low in heart, kidney, small intestine, and muscle. In primary hippocampal neurons, Tmem57 was found in neurites and their terminals, and it partially colocalized with synapsin-1, a presynaptic marker.