Enaptin also known as nesprin-1 or synaptic nuclear envelope protein 1 (syne-1) is an actin-binding protein that in humans that is encoded by the SYNE1 gene. This gene encodes a spectrin repeat containing protein expressed in skeletal and smooth muscle, and peripheral blood lymphocytes, that localizes to the nuclear membrane. Enaptin is a nuclear envelope protein found in human myocytes and synapses, which is made up of 8,797 amino acids. Enaptin is involved in the maintenance of nuclear organization and structural integrity, tethering the cell nucleus to the cytoskeleton by interacting with the nuclear envelope and with F-actin in the cytoplasm. Enaptin contains a coiled alpha-helical region and a large beta-sheet region in the upper part and at least four alpha-helices spliced together, indicating the similarity with collagen. The molecular weight of the mature protein is approximately 1,011 kDa, and it has a theoretical pI of 5.38. It has a theoretical Instability Index (II) of 51.63, indicating that it would be unstable in a test tube. The protein's in vivo half-life, the time it takes for half of the amount of protein in a cell to disappear after its synthesis in the cell, is predicted to be approximately 30 hours (in mammalian reticulocytes).