Mutational analysis of the properties of caveolin-1. A novel role for the C-terminal domain in mediating homo-typic caveolin-caveolin interactions.
Caveolin is a principal structural component of caveolae membranes in vivo. Recently, a family of caveolin-related proteins has been identified; caveolin has been retermed caveolin-1. Caveolin family members share three characteristic properties: (i) detergent insolubility at low temperatures; (ii) self-oligomerization; and (iii) incorporation into low density Triton-insoluble fractions enriched in caveolae membranes. Here, we have used a deletion mutagenesis approach as a first step toward understanding which regions of caveolin-1 contribute to its unusual properties. Two caveolin-1 deletion mutants were created that lack either the C-terminal domain (Cav-1DeltaC) or the N-terminal domain (Cav-1DeltaN); these mutants were compared with the behavior of full-length caveolin-1 (Cav-1FL) expressed in parallel. Our results show that the N-terminal domain and membrane spanning segment are sufficient to form high molecular mass oligomers of caveolin-1. However, a complete caveolin-1 molecule is required for conveying detergent insolubility and incorporation into low density Triton-insoluble complexes. These data indicate that homo-oligomerization and an intact transmembrane are not sufficient to confer detergent insolubility, suggesting an unknown role for the C-terminal domain in this process. To better understand the role of the C-terminal domain, this region of caveolin-1 (residues 135-178) was expressed as a glutathione S-transferase fusion protein in Escherichia coli. Purified recombinant glutathione S-transferase-C-Cav-1 was found to stably interact with full-length caveolin-1 but not with the two caveolin-1 deletion mutants. These results suggest that the C-terminal domain interacts with both the N-terminal and C-terminal domains of an adjacent caveolin-1 homo-oligomer. This appears to be a specific homo-typic interaction, because the C-terminal domain of caveolin-1 failed to interact with full-length forms of caveolin-2 and caveolin-3. Homo-typic interaction of the C-terminal domain with an adjacent homo-oligomer could provide a mechanism for clustering caveolin-1 homo-oligomers while excluding other caveolin family members. This type of lateral segregation event could promote caveolae membrane formation and contribute to the detergent insolubility of caveolins-1, -2, and -3.
Song
K S
KS
Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142-1479, USA.
Tang
Z
Z
Li
S
S
Lisanti
M P
MP
D000818:Animals; D001704:Biopolymers; D051242:Caveolin 1; D051243:Caveolin 2; D051244:Caveolin 3; D022461:Caveolins; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004285:Dogs; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D016296:Mutagenesis; D011092:Polyethylene Glycols / Q000494:pharmacology; D011485:Protein Binding; D017384:Sequence Deletion
D001704:Biopolymers; D051242:Caveolin 1; D051243:Caveolin 2; D051244:Caveolin 3; D022461:Caveolins; D008565:Membrane Proteins; D011092:Polyethylene Glycols