title: Thermodynamic analysis of a molecular chaperone binding to unfolded protein substrates.
abstract: Molecular chaperones are a highly diverse group of proteins that recognize and bind unfolded proteins to facilitate protein folding and prevent nonspecific protein aggregation. The mechanisms by which chaperones bind their protein substrates have been studied for decades. However, there are few reports about the affinity of molecular chaperones for their unfolded protein substrates. Thus, little is known about the relative binding affinities of different chaperones and about the relative binding affinities of chaperones for different unfolded protein substrates. Here we describe the application of SUPREX (stability of unpurified proteins from rates of H-D exchange), an H-D exchange and MALDI-based technique, in studying the binding interaction between the molecular chaperone Hsp33 and four different unfolded protein substrates, including citrate synthase, lactate dehydrogenase, malate dehydrogenase, and aldolase. The results of our studies suggest that the cooperativity of the Hsp33 folding-unfolding reaction increases upon binding with denatured protein substrates. This is consistent with the burial of significant hydrophobic surface area in Hsp33 when it interacts with its substrate proteins. The SUPREX-derived K(d) values for Hsp33 complexes with four different substrates were all found to be within the range of 3-300 nM.
authors.affiliation: Department of Chemistry, Duke University, Durham, North Carolina 27708-0346, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Xu
authors.forename: Sebastian
authors.initials: S
authors.lastname: Schmitt
authors.forename: Liangjie
authors.initials: L
authors.lastname: Tang
authors.forename: Ursula
authors.initials: U
authors.lastname: Jakob
authors.forename: Michael C
authors.initials: MC
authors.lastname: Fitzgerald
mesh_terms: D000818:Animals; D002950:Citrate (si)-Synthase / Q000737:chemistry / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D005634:Fructose-Bisphosphate Aldolase / Q000737:chemistry / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000737:chemistry / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000737:chemistry / Q000378:metabolism; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D011817:Rabbits; D013379:Substrate Specificity; D013552:Swine; D013816:Thermodynamics
chemical_list: D029968:Escherichia coli Proteins; C492165:HSP33 protein, E coli; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D007770:L-Lactate Dehydrogenase; D008291:Malate Dehydrogenase; D002950:Citrate (si)-Synthase; D005634:Fructose-Bisphosphate Aldolase