pH-dependent Interactions of the Carboxyl-terminal Helix of Steroidogenic Acute Regulatory Protein with Synthetic Membranes

Yaworsky, Dustin C.; Baker, Bo Y.; Bose, Himangshu S.; Best, Katrina B.; Jensen, Lauren B.; Bell, John D.; Baldwin, Michael A.; Miller, Walter L.

doi:10.1074/jbc.m410937200

Cited by 62 publications

(69 citation statements)

References 29 publications

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Section: C]-or Nbd-cholesterol As Wild-type Star Under Equilibrium Comentioning

confidence: 99%

“…All of these structures are characterized by four ␣-helices and nine antiparallel ␤-sheets that define a hydrophobic sterol-binding pocket (SBP). Structural modeling indicates that the position of the C-helix is stabilized by a network of hydrogen bonds with the adjacent structures, especially by a salt bridge with Asp 106 at the end of the loop between sheets ␤1 and ␤2 (residues 102-106) (10,15). Molecular dynamics simulations show that the C-helix is closely associated with this loop, but opens widely under acidic conditions (14).…”

mentioning

confidence: 99%

“…Only the COOH-terminal ␣-helix (C-helix) of StAR interacts with the OMM (10). Biophysical data show that StAR undergoes an acid-induced structural change to a molten globule state (11), and the association of StAR with the OMM is stronger under acidic conditions (10,(12)(13)(14)(15).The structure of StAR has not been determined experimentally, but the structures of three closely related proteins having "StAR-related lipid transfer" domains have been determined (16 -18) permitting the construction of computational models of StAR (10,15,16). All of these structures are characterized by four ␣-helices and nine antiparallel ␤-sheets that define a hydrophobic sterol-binding pocket (SBP).…”

mentioning

confidence: 99%

“…Nevertheless, StAR acts on the OMM, and is inactive inside the mitochondrion: deletion of 62 NH 2 -terminal residues yields a protein (N-62 StAR) that remains in the cytoplasm, yet retains full biologic activity (8), and affixing StAR to the OMM yields constituitive activity, whereas localizing it to the intramembranous space or the matrix side of the IMM ablates activity (9). Only the COOH-terminal ␣-helix (C-helix) of StAR interacts with the OMM (10). Biophysical data show that StAR undergoes an acid-induced structural change to a molten globule state (11), and the association of StAR with the OMM is stronger under acidic conditions (10,(12)(13)(14)(15).…”

mentioning

confidence: 99%

“…The structure of StAR has not been determined experimentally, but the structures of three closely related proteins having "StAR-related lipid transfer" domains have been determined (16 -18) permitting the construction of computational models of StAR (10,15,16). All of these structures are characterized by four ␣-helices and nine antiparallel ␤-sheets that define a hydrophobic sterol-binding pocket (SBP).…”

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confidence: 99%

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Cholesterol Binding Does Not Predict Activity of the Steroidogenic Acute Regulatory Protein, StAR

Baker

Epand

et al. 2007

Journal of Biological Chemistry

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Steroidogenic acute regulatory protein (StAR) stimulates adrenal and gonadal steroidogenesis by increasing the influx of cholesterol into mitochondria, where it is converted to pregnenolone to initiate steroidogenesis. StAR acts on the outer mitochondrial membrane where each molecule stimulates the mitochondrial import of several hundred molecules of cholesterol, but the precise mechanism of the action of StAR remains uncertain. StAR has a sterol-binding pocket that can accommodate one molecule of cholesterol. Direct assays show that StAR can bind cholesterol with stoichiometry approaching 1:1, and several disease-causing mutants with decreased or absent activity have correspondingly decreased cholesterol binding. We show that the StAR mutant R182L, which causes severe disease and is devoid of measurable activity in transfected cells or with isolated steroidogenic mitochondria, nevertheless, can bind as much [ C]-or NBD-cholesterol as wild-type StAR under equilibrium conditions and can transfer cholesterol between liposomes in vitro.Similarly, the artificial mutant S195A had 46.5% of the activity of wild-type StAR but bound cholesterol indistinguishably from wild-type. Competition assays showed that the rate of binding (t1 ⁄ 2on ) for R182L was only 36% of the wild-type and the rate of dissociation (t1 ⁄ 2off ) was 57% of wild-type, whereas the t1 ⁄ 2on and t1 ⁄ 2off for S195A and S195D were essentially the same for wild-type. These data indicate that cholesterol binding and transfer activities are distinct from its activity to induce steroidogenesis. StAR appears to act by other mechanisms in addition to cholesterol binding.In the adrenal and gonad, the steroidogenic acute regulatory protein (StAR) 2 facilitates the flow of cholesterol from the outer mitochondrial membrane (OMM) to the inner mitochondrial membrane (IMM) where it is converted to pregnenolone by the cholesterol side chain cleavage enzyme, P450scc, thus initiating the synthesis of steroid hormones (1, 2). Loss of StAR activity ablates adrenal and gonadal steroidogenesis, causing lifethreatening congenital lipoid adrenal hyperplasia (3). Fulllength StAR is expressed as a 37-kDa, 285-residue phosphoprotein having a mitochondrial leader sequence that is cleaved to a 30-kDa intramitochondrial form (4 -7). Nevertheless, StAR acts on the OMM, and is inactive inside the mitochondrion: deletion of 62 NH 2 -terminal residues yields a protein (N-62 StAR) that remains in the cytoplasm, yet retains full biologic activity (8), and affixing StAR to the OMM yields constituitive activity, whereas localizing it to the intramembranous space or the matrix side of the IMM ablates activity (9). Only the COOH-terminal ␣-helix (C-helix) of StAR interacts with the OMM (10). Biophysical data show that StAR undergoes an acid-induced structural change to a molten globule state (11), and the association of StAR with the OMM is stronger under acidic conditions (10,(12)(13)(14)(15).The structure of StAR has not been determined experimentally, but the structures of three clos...

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Section: C]-or Nbd-cholesterol As Wild-type Star Under Equilibrium Comentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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confidence: 99%

mentioning

confidence: 99%

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