title: Differential phosphorylation-based regulation of αB-crystallin chaperone activity for multipass transmembrane proteins.
abstract: We have previously shown that αB-crystallin (CRYAB), a small heat shock protein (sHsp) that prevents irreversible aggregation of unfolded protein by an ATP-independent chaperone activity, plays a pivotal role in the biogenesis of multipass transmembrane proteins (TMPs) assisting their folding from the cytosolic side of the endoplasmic reticulum (ER) (D'Agostino et al., 2013). Here we present evidence, based on phosphomimetic substitutions, that the three phosphorytable serine residues at position 19, 45 and 59 of CRYAB play a different regulatory role in this novel chaperone activity: S19 and S45 have a strong inhibitory effect, either alone or in combination, while S59 has not and counteracts the inhibition caused by single phosphomimetic substitutions at S19 and S45. Interestingly, all phosphomimetic substitutions determine the formation of smaller oligomeric complexes containing CRYAB, indicating that the inhibitory effect seen for S19 and S45 cannot be ascribed to the reduction of oligomerization frequently associated to a decreased chaperone activity. These results indicate that phosphorylation finely regulates the chaperone activity of CRYAB with multipass TMPs and suggest a pivotal role for S59 in this process.
authors.affiliation: Department of Molecular Medicine and Medical Biotechnology, University of Naples Federico II, Naples, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: Ciano
authors.affiliation: Department of Molecular Medicine and Medical Biotechnology, University of Naples Federico II, Naples, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Allocca
authors.affiliation: Department of Molecular Medicine and Medical Biotechnology, University of Naples Federico II, Naples, Italy.
authors.forename: Maria Camilla
authors.initials: MC
authors.lastname: Ciardulli
authors.affiliation: Department of Molecular Medicine and Medical Biotechnology, University of Naples Federico II, Naples, Italy.
authors.forename: Lucrezia
authors.initials: L
authors.lastname: Della Volpe
authors.affiliation: Department of Molecular Medicine and Medical Biotechnology, University of Naples Federico II, Naples, Italy. Electronic address: bonatti@unina.it.
authors.forename: Stefano
authors.initials: S
authors.lastname: Bonatti
authors.affiliation: Department of Molecular Medicine and Medical Biotechnology, University of Naples Federico II, Naples, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: D'Agostino
mesh_terms: D045744:Cell Line, Tumor; D018076:DNA, Complementary / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism*; D016296:Mutagenesis; D009154:Mutation; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D038203:alpha-Crystallin B Chain / Q000378:metabolism*
chemical_list: D018076:DNA, Complementary; D008565:Membrane Proteins; D018832:Molecular Chaperones; D038203:alpha-Crystallin B Chain; D049452:Green Fluorescent Proteins; D012694:Serine
keywords: Chaperone activity; Multipass transmembrane proteins; Phosphorylation; αB-crystallin/HspB5/CRYAB