Structure-function analysis of the heat shock factor-binding protein reveals a protein composed solely of a highly conserved and dynamic coiled-coil trimerization domain.
Heat shock factor-binding protein (HSBP) 1 is a small, evolutionarily conserved protein originally identified in a yeast two-hybrid screen using the trimerization domain of heat shock factor (HSF) 1 as the bait. Similar in size to HSF1 trimerization domain, human HSBP1 contains two arrays of hydrophobic heptad repeats (designated HR-N and HR-C) characteristic of coiled-coil proteins. Proteins of the HSBP family are relatively small (<100 residues), comprising solely a putative coiled-coil oligomerization domain without any other readily recognizable structural or functional motif. Our biophysical and biochemical characterization of human HSBP1 reveals a cooperatively folded protein with high alpha-helical content and moderate stability. NMR analyses reveal a single continuous helix encompassing both HR-N and HR-C in the highly conserved central region, whereas the less conserved carboxyl terminus is unstructured and accessible to proteases. Unlike previously characterized coiled-coils, backbone 15N relaxation measurements implicate motional processes on the millisecond time scale in the coiled-coil region. Analytical ultracentrifugation and native PAGE studies indicate that HSBP1 is predominantly trimeric over a wide concentration range. NMR analyses suggest a rotationally symmetric trimer. Because the highly conserved hydrophobic heptad repeats extend over 60% of HSBP1, we propose that HSBP most likely regulates the function of other proteins through coiled-coil interactions.
Tai
Li-Jung
LJ
Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Evanston, Illinois 60208, USA.
McFall
Sally M
SM
Huang
Kai
K
Demeler
Borries
B
Fox
Sue G
SG
Brubaker
Kurt
K
Radhakrishnan
Ishwar
I
Morimoto
Richard I
RI
D000595:Amino Acid Sequence; D002850:Chromatography, Gel; D017124:Conserved Sequence; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000502:physiology; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008969:Molecular Sequence Data; D017510:Protein Folding; D017433:Protein Structure, Secondary; D020449:Repetitive Sequences, Amino Acid; D013329:Structure-Activity Relationship; D014461:Ultracentrifugation
C113285:HSBP1 protein, human; D006360:Heat-Shock Proteins