Molecular architecture of the Bardet–Biedl syndrome protein 2-7-9 subcomplex

• Published in: The Journal of biological chemistry Vol. 294; no. 44; pp. 16385 - 16399
• Main Authors: Ludlam, W. Grant, Aoba, Takuma, Cuéllar, Jorge, Bueno-Carrasco, M. Teresa, Makaju, Aman, Moody, James D., Franklin, Sarah, Valpuesta, José M., Willardson, Barry M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.11.2019; American Society for Biochemistry and Molecular Biology
• Subjects: Adaptor Proteins, Signal Transducing - metabolism; Bardet-Biedl syndrome; Bardet-Biedl Syndrome - metabolism; Cilia - metabolism; Cilia transport; ciliopathy; Cytoskeletal Proteins - metabolism; electron microscopy (EM); HEK293 Cells; homology modeling; Humans; integrated modeling; mass spectrometry (MS); Mass Spectrometry - methods; Microscopy, Electron - methods; Models, Molecular; Mutation; protein assembly; protein complex; protein cross-linking; Protein Structure and Folding; Proteins - metabolism; homology modeling; Cilia transport; Bardet-Biedl syndrome; protein complex; protein assembly; protein cross-linking; mass spectrometry (MS); electron microscopy (EM); ciliopathy; integrated modeling
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.RA119.010150

Bardet-Biedl syndrome (BBS) is a genetic disorder characterized by malfunctions in primary cilia resulting from mutations that disrupt the function of the BBSome, an 8-subunit complex that plays an important role in protein transport in primary cilia. To better understand the molecular basis of BBS, here we used an integrative structural modeling approach consisting of EM and chemical cross-linking coupled with MS analyses, to analyze the structure of a BBSome 2-7-9 subcomplex consisting of three homologous BBS proteins, BBS2, BBS7, and BBS9. The resulting molecular model revealed an overall structure that resembles a flattened triangle. We found that within this structure, BBS2 and BBS7 form a tight dimer through a coiled-coil interaction and that BBS9 associates with the dimer via an interaction with the α-helical domain of BBS2. Interestingly, a BBS-associated mutation of BBS2 (R632P) is located in its α-helical domain at the interface between BBS2 and BBS9, and binding experiments indicated that this mutation disrupts the BBS2-BBS9 interaction. This finding suggests that BBSome assembly is disrupted by the R632P substitution, providing molecular insights that may explain the etiology of BBS in individuals harboring this mutation.