Abstract
Caveolae are 50-100 nm invaginations in the plasma membrane of many cell types that play a critical role in signal transduction. Caveolin-1 is a 21 kD integral membrane protein that is required for the formation of caveolae. Caveolin-1 is thought to adopt an unusual horseshoe topology in the membrane where the N- and C- termini are cytoplasmic. Caveolin-1 has 4 native tryptophan residues in this region (W85, W98, W115, and W128) that can be used as reporters of the micro-environment of the polypeptide chain. Caveolin-1 single tryptophan mutants were successfully reconstituted into CHAPSO/DMPC bicelles. Fluorescence emission measurements were performed on each mutant and analysis of these spectra indicated that tryptophan residues 85 and 128 are in the head group region of the lipid bilayer with λmax values of 344.4 ± 2.4 nm and 338.2 ± 0.6 nm respectively, and tryptophan residues 98 and 115 are inserted into the hydrophobic core with λmax values of 334.4 ± 0.2 nm and 330.2 ± 1.0 nm, respectively. The information gleaned from these studies was supported by MD simulations performed on caveolin-1 in a DMPC bilayer. These data together support the postulation that caveolin-1 contains a membrane embedded turn.
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