Chaperone activity of cytosolic small heat shock proteins from wheat.
Small Hsps (sHsps) and the structurally related eye lens alpha-crystallins are ubiquitous stress proteins that exhibit ATP-independent molecular chaperone activity. We studied the chaperone activity of dodecameric wheat TaHsp16.9C-I, a class I cytosolic sHsp from plants and the only eukaryotic sHsp for which a high resolution structure is available, along with the related wheat protein TaHsp17.8C-II, which represents the evolutionarily distinct class II plant cytosolic sHsps. Despite the available structural information on TaHsp16.9C-I, there is minimal data on its chaperone activity, and likewise, data on activity of the class II proteins is very limited. We prepared purified, recombinant TaHsp16.9C-I and TaHsp17.8C-II and find that the class II protein comprises a smaller oligomer than the dodecameric TaHsp16.9C-I, suggesting class II proteins have a distinct mode of oligomer assembly as compared to the class I proteins. Using malate dehydrogenase as a substrate, TaHsp16.9C-I was shown to be a more effective chaperone than TaHsp17.8C-II in preventing heat-induced malate dehydrogenase aggregation. As observed by EM, morphology of sHsp/substrate complexes depended on the sHsp used and on the ratio of sHsp to substrate. Surprisingly, heat-denaturing firefly luciferase did not interact significantly with TaHsp16.9C-I, although it was fully protected by TaHsp17.8C-II. In total the data indicate sHsps show substrate specificity and suggest that N-terminal residues contribute to substrate interactions.
Basha
Eman
E
Department of Biochemistry & Molecular Biophysics, University of Arizona, Tucson, AZ 85721-0106, USA.
Lee
Garrett J
GJ
Demeler
Borries
B
Vierling
Elizabeth
E
D000595:Amino Acid Sequence; D000818:Animals; D001517:Coleoptera / Q000201:enzymology; D003600:Cytosol / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D008156:Luciferases / Q000737:chemistry / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000737:chemistry / Q000378:metabolism; D008854:Microscopy, Electron; D018832:Molecular Chaperones / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010940:Plant Proteins / Q000737:chemistry / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013379:Substrate Specificity; D014908:Triticum / Q000737:chemistry*; D014461:Ultracentrifugation / Q000379:methods
D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D010940:Plant Proteins; D011994:Recombinant Proteins; D008291:Malate Dehydrogenase; D008156:Luciferases