StAR-related lipid transfer domain protein 7 (STARD7) or gestational trophoblastic tumor gene-1 (GTT1) is a lipid

Lipid

Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...

 transporter that specifically binds and transports phosphatidylcholine

Phosphatidylcholine

Phosphatidylcholines are a class of phospholipids that incorporate choline as a headgroup.They are a major component of biological membranes and can be easily obtained from a variety of readily available sources such as egg yolk or soy beans from which they are mechanically extracted or chemically...

 between membranes.

Function and tissue distribution

StarD7 is found in the cytosol

Cytosol

The cytosol or intracellular fluid is the liquid found inside cells, that is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into compartments....

 and associated with the mitochondrion

Mitochondrion

In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...

. When overproduced in the cell, mitochondrial levels of phosphatidylcholine rise. High levels of the protein are found in tumor

Tumor

A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...

 cells compared to normal cells, suggesting a role in cell proliferation.

Structure

There are two forms of StarD7: StarD7-I and StarD7-II. The former is 295 amino acids long. StarD7-I possesses an additional 75 amino acids at its amino-terminus, which form a signaling sequence that targets it to the outer membrane of the mitochondrion.

StarD7 contains a StAR-related transfer domain

StAR-related transfer domain

START is a lipid-binding domain in StAR, HD-ZIP and signalling proteins. The archetypical domain is found in StAR , a mitochondrial protein that is synthesized in steroid-producing cells. StAR and initiates steroid production by mediating the delivery of cholesterol to the first enzyme in...

 (START), from which it derives its name. Moreover, the protein is a member of the predominantly phosphatidylcholine transporter subfamily of START proteins, the StarD2 subfamily. It shares 25% sequence identity with StarD2.