molecular mechanisms underlying BiP-mediated gating of the Sec61 translocon of the endoplasmic reticulum

• Published in: The Journal of cell biology 2005-01, Vol.168 (3), p.389-399
• Main Authors: Alder, Nathan N, Shen, Ying, Brodsky, Jeffrey L, Hendershot, Linda M, Johnson, Arthur E
• Format: Article
• Language: English
• Subjects: Adenosine Diphosphate - metabolism; Adenosine Diphosphate - pharmacology; Adenosine triphosphatase; Adenosine triphosphatases; Adenosine Triphosphatases - drug effects; Adenosine Triphosphatases - metabolism; Adenosine Triphosphate - metabolism; Adenosine Triphosphate - pharmacology; Animals; Binding sites; Binding Sites - genetics; Binding Sites - physiology; Binding, Competitive; Cellular biology; Cricetinae; Endoplasmic reticulum; Endoplasmic Reticulum - metabolism; Endoplasmic Reticulum - physiology; Fluorescence; Fluorescence Polarization; Fluorescent Dyes - chemistry; Fungal Proteins - metabolism; Heat-Shock Proteins - genetics; Heat-Shock Proteins - metabolism; Heat-Shock Proteins - physiology; HSP70 Heat-Shock Proteins - metabolism; Hydrolysis; Iodine - chemistry; Membrane proteins; Membrane Proteins - metabolism; Membrane Proteins - physiology; Microsomes; Microsomes - metabolism; Models, Biological; Molecular Chaperones - genetics; Molecular Chaperones - metabolism; Molecular Chaperones - physiology; Mutation; Nucleotides; Peptides - chemistry; Peptides - pharmacology; Prolactin - chemistry; Prolactin - metabolism; Protein Binding; Protein Conformation - drug effects; Protein Precursors - chemistry; Protein Precursors - metabolism; Protein Structure, Tertiary - physiology; Protein transport; Protein Transport - physiology; Proteins; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Ribosomes; SEC Translocation Channels; Spectrometry, Fluorescence; Yeasts
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.200409174

The Sec61 translocon of the endoplasmic reticulum membrane forms an aqueous pore that is gated by the lumenal Hsp70 chaperone BiP. We have explored the molecular mechanisms governing BiP-mediated gating activity, including the coupling between gating and the BiP ATPase cycle, and the involvement of the substrate-binding and J domain-binding regions of BiP. Translocon gating was assayed by measuring the collisional quenching of fluorescent probes incorporated into nascent chains of translocation intermediates engaged with microsomes containing various BiP mutants and BiP substrate. Our results indicate that BiP must assume the ADP-bound conformation to seal the translocon, and that the reopening of the pore requires an ATP binding-induced conformational change. Further, pore closure requires functional interactions between both the substrate-binding region and the J domain-binding region of BiP and membrane proteins. The mechanism by which BiP mediates translocon pore closure and opening is therefore similar to that in which Hsp70 chaperones associate with and dissociate from substrates.