A new N-terminal recognition domain in caveolin-1 interacts with sterol carrier protein-2 (SCP-2).
Although plasma membrane domains, such as caveolae, provide an organizing principle for signaling pathways and cholesterol homeostasis in the cell, relatively little is known regarding specific mechanisms, whereby intracellular lipid-binding proteins are targeted to caveolae. Therefore, the interaction between caveolin-1 and sterol carrier protein-2 (SCP-2), a protein that binds and transfers both cholesterol and signaling lipids (e.g., phosphatidylinositides and sphingolipids), was examined by yeast two-hybrid, in vitro binding and fluorescence resonance energy transfer (FRET) analyses. Results of the in vivo and in vitro assays identified for the first time the N-terminal amino acids (aa) 1-32 amphipathic alpha helix of SCP-2 functionally interacted with caveolin-1. This interaction was independent of the classic caveolin-1 scaffolding domain, in which many signaling proteins interact. Instead, SCP-2 bound caveolin-1 through a new domain identified in the N-terminal domain of caveolin-1 between aa 34-40. Modeling studies suggested that electrostatic interactions between the SCP-2 N-terminal aa 1-32 amphipathic alpha-helical domain (cationic, positively charged face) and the caveolin-1 N-terminal aa 33-59 alpha helix (anionic, negatively charged face) may significantly contribute to this interaction. These findings provide new insights on how SCP-2 enhances cholesterol retention within the cell as well as regulates the distribution of signaling lipids, such as phosphoinositides and sphingolipids, at plasma membrane caveolae.
Parr
Rebecca D
RD
Department of Pathobiology, Texas A&M University, TVMC, College Station, Texas 77843-4467, USA.
Martin
Gregory G
GG
Hostetler
Heather A
HA
Schroeder
Megan E
ME
Mir
Kiran D
KD
Kier
Ann B
AB
Ball
Judith M
JM
Schroeder
Friedhelm
F
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D051242:Caveolin 1 / Q000737:chemistry* / Q000378:metabolism; D002460:Cell Line; D031541:Fluorescence Resonance Energy Transfer; D021962:Membrane Microdomains / Q000737:chemistry; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000737:chemistry; D017434:Protein Structure, Tertiary; D020798:Two-Hybrid System Techniques
D002352:Carrier Proteins; D051242:Caveolin 1; D011498:Protein Precursors; C072087:sterol carrier proteins