MLN64

StAR-related lipid transfer (START) domain containing 3
Identifiers
Symbol	STARD3
Entrez	10948
HUGO	17579
OMIM	607048
RefSeq	NM_006804
UniProt	Q14849
Other data
Locus	Chr. 17 q11-q12

StAR-related lipid transfer domain protein 3 (STARD3) also known as metastatic lymph node 64 protein (MLN64) is a late endosomal integral membrane protein involved in cholesterol transport.

MLN64 is hypothesized to regulate cholesterol transport between the late endosome where it is tethered and cytoplasmic membranes. Some data further suggest that endogenous MLN64 can cause cholesterol transport to the mitochondria.

The closest homolog to MLN64 is the steroidogenic acute regulatory protein (StAR/StarD1), which initiates the production of steroids by moving cholesterol inside the . Thus, MLN64 is also proposed to move cholesterol inside the mitochondria under certain conditions to initiate StAR-independent steroidogenesis, such as in the human placenta which lacks StAR yet produces steroids. This functional role is supported by evidence that MLN64 expression can stimulate steroid production in a model cell system.

A recent study indicates that this protein also specifically binds lutein in the retina.

Its C-terminus contains a StAR-related transfer domain (START) that is homologous to the StAR. X-ray crystallography of the C-terminus indicates that this domain forms a pocket that can bind cholesterol. This places MLN64 within the StarD1/D3 subfamily of START domain-containing proteins.

The N-terminus consists of a MENTAL (MLN64 N-terminal) domain similar to the protein MLN64 N-terminal homologue (MENTHO) with unclear function. This domain is buried in the late endosomal membrane and may associate with the same domain in MENTHO.

MLN64 is expressed in all tissues in the body at various levels. In the brain, MLN64 is detectable in many but not all cells. Many malignant tumors highly express MLN64 as a result of its gene being part of a Her2/erbB2-containing gene locus that is duplicated.

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