Steriod acute regulator protein (StAR) is the protein involved in the time-limiting step of stereogenesis since one molecule StAR must be produced to transport one molecule cholesterol from the cell membrane to the mitochondrium. There, the side-chain cleavage enzyme converts the cholesterol to pregnenolone to begin the steroid synthesis for androgens and estrogens, mineralocorticoids and cortisols. StAR is therefore an important molecule for the Endocrinologist. Whereever StAR is expressed, steroids are supposed to be made. Its characteristic structure – a pocket to acquire just one molecule of cholesterol – has been crystallized and determined by X-ray spectrometry. What is much less known that it has homologues throughout the animal kingdom, even other taxa share the structure which is thus fairly old and that is used not only for cholesterol, but for numerous lipids, too.
Strange enough, a molecule which is at the beginning of a specialized reaction chain such as steroidogenesis is widely used. Sometimes the introduction to an article is an eye-opener: In Current Biology the paper by Schrick shows just such a case. They are concerned with StAR homologues in the plant Arabidopsis and their role as transcription factors. Maybe not so interesting to the general audience, but the introduction resumes the role of StAR and StAR-like proteins fairly well. Recommended.