title: Chemical cross-linking of the chloroplast localized small heat-shock protein, Hsp21, and the model substrate citrate synthase.
abstract: The molecular mechanism whereby the small heat-shock protein (sHsp) chaperones interact with and prevent aggregation of other proteins is not fully understood. We have characterized the sHsp-substrate protein interaction at normal and increased temperatures utilizing a model substrate protein, citrate synthase (CS), widely used in chaperone assays, and a dodecameric plant sHsp, Hsp21, by chemical cross-linking with 3,3'-Dithiobis[sulfosuccinimidylpropionate] (DTSSP) and mass spectrometric peptide mapping. In the absence of CS, the cross-linker captured Hsp21 in dodecameric form, even at increased temperature (47 degrees C). In the presence of equimolar amounts of CS, no Hsp21 dodecamer was captured, indicating a substrate-induced Hsp21 dodecamer dissociation by equimolar amounts of CS. Cross-linked Hsp21-Hsp21 dipeptides indicated an exposure of the Hsp21 C-terminal tails and substrate-binding sites normally covered by the C terminus. Cross-linked Hsp21-CS dipeptides mapped to several sites on the surface of the CS dimer, indicating that there are numerous weak and short-lived interactions between Hsp21 and CS, even at normal temperatures. The N-terminal arms especially interacted with a motif in the CS dimer, which is absent in thermostable forms of CS. The cross-linking data suggest that the presence of substrate rather than temperature influences the conformation of Hsp21.
authors.affiliation: Department of Biochemistry, Lund University, Sweden. emma.ahrman@biochemistry.lu.se
authors.forename: Emma
authors.initials: E
authors.lastname: Ahrman
authors.forename: Wietske
authors.initials: W
authors.lastname: Lambert
authors.forename: J Andrew
authors.initials: JA
authors.lastname: Aquilina
authors.forename: Carol V
authors.initials: CV
authors.lastname: Robinson
authors.forename: Cecilia Sundby
authors.initials: CS
authors.lastname: Emanuelsson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002736:Chloroplasts / Q000378:metabolism*; D002950:Citrate (si)-Synthase / Q000737:chemistry / Q000378:metabolism*; D019281:Dimerization; D050888:Heat-Shock Proteins, Small / Q000737:chemistry* / Q000378:metabolism; D013058:Mass Spectrometry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013552:Swine
chemical_list: D050888:Heat-Shock Proteins, Small; D010455:Peptides; D010940:Plant Proteins; D002950:Citrate (si)-Synthase