Lysosomal Trafficking Regulator (LYST) gene codes for a protein that plays a major role in the transport of molecules into and from lysosomes and lysosome-related organelles. Although, the exact mechanism of this protein is not known, there is evidence to suggest that the protein may help determine the size of lysosomes and regulate their movement within cells. It may also be involved in the sorting of endosomal proteins into late multi-vesicular endosomes by a mechanism involving microtubules. The LYST protein is known to interact with several other proteins involved in membrane fusion events, such as v-SNAREs, t-SNAREs, Casein Kinase II, and other signaling proteins.

Abnormalities in the proper functioning of this protein lead to the development of abnormally large lysosomes. In the immune cells, these abnormal lysosomes could interfere with the immune response to pathogens. In the platelets, these abnormal lysosomes result in bruising and bleeding, while in skin, eye, and hair cells, the abnormal melanosomes can trap too much melanin resulting in lack of pigmentation. In fact, mutations in the LYST gene have been found to cause Chediak Higashi syndrome, an autosomal recessive disease characterized by oculocutaneous albinism, recurrent infections, abnormal bruising and bleeding, and a progressive primary neurological disease.

The LYST gene is located on the long arm of chromosome 1. It spans a total length of 222 Kb, and contains 53 exons, 51 of which are coding. The LYST protein is a 430 KDa cytoplasmic protein that is made up of 3,801 amino acids. This protein is a member of the BEACH (Beige and Chediak-Higashi) family of proteins. These proteins are characterized by the presence of a BEACH motif, which consists of a WIDL-enriched sequence followed by several WD-40 domains. This motif lies at the C-terminal end of the LYST protein, while at the N-terminus of the protein is a series of ARM/HEAT repeat, which is known to play a role in membrane identification.

More than 40 mutations, including missense and nonsense mutations and indels, in the LYST gene have been identified to date. As expected, loss of function mutations have been found to be associated with severe childhood-onset form of Chediak-Higashi syndrome, while the missense mutations are associated with a milder adolescent or adult-onset form of the disorder.