Cholesterol interaction with the related steroidogenic acute regulatory lipid‐transfer (START) domains of StAR (STARD1) and MLN64 (STARD3)

Abstract

The steroidogenic acute regulatory (StAR)‐related lipid transfer (START) domains are found in a wide range of proteins involved in intracellular trafficking of cholesterol and other lipids. Among the START proteins are the StAR protein itself (STARD1) and the closely related MLN64 protein (STARD3), which both function in cholesterol movement. We compared the cholesterol‐binding properties of these two START domain proteins. Cholesterol stabilized STARD3‐START against trypsin‐catalyzed degradation, whereas cholesterol had no protective effect on STARD1‐START. [3H]Azocholestanol predominantly labeled a 6.2 kDa fragment of STARD1‐START comprising amino acids 83–140, which contains residues proposed to interact with cholesterol in a hydrophobic cavity. Photoaffinity labeling studies suggest that cholesterol preferentially interacts with one side wall of this cavity. In contrast, [3H]azocholestanol was distributed more or less equally among the polypeptides of STARD3‐START. Overall, our results provide evidence for differential cholesterol binding of the two most closely related START domain proteins STARD1 and STARD3.

The role of mitochondrial fusion and StAR phosphorylation in the regulation of StAR activity and steroidogenesis

“…It is hard to elucidate a putative model to describe the effect of the Ser232 phosphorylation on StAR affinity for cholesterol. StAR molecular structure has been partially studied (Mathieu et al, 2002;Petrescu et al, 2001;Tsujishita and Hurley, 2000;Yaworsky et al, 2005) and it can be inferred that the Ser232 residue is localized in one of the last β barrels of the START domain (Reitz et al, 2008;Yaworsky et al, 2005). It is well known that amino acidic phosphorylation involves changes in protein stability and regulates affinity with other components.…”

“…Cholesterol release could result from a pH-dependent transition to a molten globule structure, involving the loss of association between the C-terminal α-helix and lipid molecules in the OMM. Under acidic pH conditions, the cholesterol affinity for START domain is significantly decreased (Reitz et al, 2008). Thus, ERK phosphorylation of StAR could determine a local decrease in pH, leading to a putative conformational change on StAR, rendering the protein slightly more capable of releasing its bound cholesterol.…”

Cholesterol lowering drug may influence cellular immune response by altering MHC II function

“…Binding of cholesterol with TM-MHC-II was monitored by the change in fl uorescence spectrum of NBD-cholesterol ( 30,31 ). This revealed that the fl uorescence emission spectrum of NBD-cholesterol undergoes a large increase in intensity in the presence of TM-MHC-II in PBS containing 2 mM CHAPS (detergent) ( Fig.…”

“…Similarly, increasing concentration of NBD-cholesterol was added to PBS and the 10 nM concentration of peptide added to PBS as a control. NBD-cholesterol was excited at 470 nm and emission measured from 500 to 570 nm ( 30,31 ). The buffer controls were subtracted from fl uorescence data.…”

STARD3/MLN64 is Striving at Membrane Contact Sites: Intracellular Cholesterol Trafficking for Steroidogenesis in Human Placental Cells

“…This observation casts doubt on whether the START domain fragment directly recruits and transports cholesterol to the mitochondria. Trypsin-catalyzed proteolytic analysis, in contrast, indicates differential cholesterol binding by each START domain [23]. Thus, an alternative idea is that the START domains of StAR and STARD3 differ slightly in their ability to transport cholesterol to mitochondria.…”