Modeling of caveolin Klaus Fiedler

A		Caveolin-1 was previously found to be similar to PITPalpha (Fiedler, 2008). The MODELLER algorithm was used here subjecting loops to modeling. Global interaction of cholesterol and local CRAC binding was analyzed. An initial loop was modeled and resulted in slight variation of the signature motif of VIP-21 / caveolin-1 (within amino acids 60-80) (brown). A The final results were generated with modeling residues 1-20, 44-86, 123-141, 152-178 and were tested for cholesterol and further docking of lipids. B Cholesterol is shown as spherical molecule in the newly described binding cavitas. CoA-acyl thioester bound to the binding cavity with intermediate to high affinity. The primary binding hit is shown in global interaction. Part of the surface has been sliced (clipped). C Putative binding interaction of VIP-21 to cholesterol in the vicinity of the membrane span. D CRAC binding of cholesterol was shown with primary hit within the binding cavity with local area interaction. The residues within 4 Å of the structure were labeled with Val94, Thr95, Tyr97, Phe99, Arg101 and Leu102, Ala105, Leu106 extending into the membrane span of caveolin and to Ile18 of the N-terminus. CRAC lipid binding was variable with some hits and hydrophobic interactions on the backside of the molecule. E Disease Mapping onto the caveolin surface by analogy; the cholesterol binding site is labeled. The CRAC-binding site on the backside of the 180° turned molecule and the Y14 residue (src-kinase substrate) are not shown. The disease causing mutations in caveolin-3 were indicated in equivalent positions on the caveolin-1 protein after sequence comparison. Residues in the proximity of cholesterol (4 Å) are shown with underlayed color. A full summary of available data on natural gene variants is on Ensembl.org. Disease mapping was done exclusively with reference to NP Refsequences. E	Caveolin was previously shown to interact with NADH-cytochrome B5 reductase in extract from lung apical endothelial plasmalemma (Chatenay-Rivauday et al., 2004). See overview for putative involvement of the cytochrome B5 reductase in the cholesterol biosynthetic pathway. CRAC site interactions will in the future be further analyzed for binding of cholesterol biosynthetic pathway intermediates. F	F Caveolin mutants implicated in various diseases were measured in docking affinity to cholesterol. Binding of cholesterol to the wildtype protein and mutants indicated in one-letter amino acid code and position (caveolin-1 lettering). Green indicates wildtype or variations of caveolin-1, red shows mutant proteins that are analogous to structural replacement of caveolin-3 amino acid residues there implicated in limb girdle muscular dystrophy (LGMD)(see Table II) and/or HyperCKemia (HyperCK) or Rippling Muscle Disease (RMD). Violet indicates the breast cancer implicated mutants of caveolin-1. Orange indicates the Sudden Infant Death Syndrome (SIDS) / LGMD mutant within caveolin-3. Light blue shows mutants synthetically constructed without known wildtype isoform or analogue in caveolin-1 or -3 (see Ensembl variation tables cav-1 and cav-3). Breast cancer mutant Pro132Leu analogous in sequence to caveolin-1 and to caveolin-3, and involved in LGMD in caveolin-3, is indicated in dark blue. The new breast tumor mutation Phe107Leu also implicated in SIDS is shown in light brown. Binding was modeled with global cavity-docking (F) and local CRAC-docking (G). Caveolin-1 was compared by homology search with caveolin-3 (Cav-1, Cav-3) and RefSequence aligned residues that are, due to 61.6% identity likely in equivalent locations in structure, are indicated in column 3 (Cav-1). Column 4 (Conserved Cav1/2/3) are conserved residues. Cav-1 in the first column indicates disease mutations suggested based on a recent analysis.
B C
D			G		The Phe107Leu mutation implicated in breast cancer in cav1 may interfere with the structural coupling of the intermediate affinity cholesterol binding to CRAC and the on-reaction of the main binding pocket; in other caveolins sterols of a different type may require different coupling residues. It is interesting to note that natural variants of caveolin show a higher affinity to cholesterol if considering the established and newly modeled CRAC binding. I expect that caveolin may require cholesterol for its travel through the cellular membrane and cytoplasmic system – also the release from the membrane and import/localization to the nucleus may implicate cholesterol.
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