ABSTRACT
Yeast Hsp104 is an AAA+ chaperone that rescues proteins from the aggregated state. Six protomers associate to form the functional hexamer. Each protomer contains two AAA+ modules, NBD1 and NBD2. Hsp104 converts energy provided by ATP into mechanical force used to thread polypeptides through its axial channel, thereby disrupting protein aggregates. But how the action of its 12 AAA+ domains is co-ordinated to catalyze disaggregation remained unexplained. Here, we identify a sophisticated allosteric network consisting of three distinct pathways that senses the nucleotide state of AAA+ modules and transmits this information across the Hsp104 hexamer. As a result of this communication, NBD1 and NBD2 each adopt two distinct conformations (relaxed and tense) that are reciprocally regulated. The key element in the network is the NBD1-ATP state that enables Hsp104 to switch from a barely active [(T)(R)] state to a highly active [(R)(T)] state. This concerted switch involves both cis and trans protomer interactions and provides Hsp104 with the mechanistic scaffold to catalyze disaggregation. It prepares the chaperone for polypeptide binding and activates NBD2 to generate the power strokes required to resolve protein aggregates. ATP hydrolysis in NBD1 resolves the high affinity [(R)(T)] state and switches the chaperone back into the low affinity [(T)(R)] state. Our model integrates previously unexplained observations and provides the first comprehensive map of nucleotide-related allosteric signals in a class-1 AAA+ protein.
Subject(s)
Adenosine Triphosphate/chemistry , HSC70 Heat-Shock Proteins/chemistry , HSP40 Heat-Shock Proteins/chemistry , Heat-Shock Proteins/chemistry , Models, Chemical , Multienzyme Complexes/chemistry , Saccharomyces cerevisiae Proteins/chemistry , Adenosine Triphosphate/genetics , Adenosine Triphosphate/metabolism , Allosteric Regulation/physiology , Escherichia coli , HSC70 Heat-Shock Proteins/genetics , HSC70 Heat-Shock Proteins/metabolism , HSP40 Heat-Shock Proteins/genetics , HSP40 Heat-Shock Proteins/metabolism , Heat-Shock Proteins/genetics , Heat-Shock Proteins/metabolism , Humans , Hydrolysis , Multienzyme Complexes/genetics , Multienzyme Complexes/metabolism , Protein Structure, Tertiary , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Saccharomyces cerevisiae Proteins/genetics , Saccharomyces cerevisiae Proteins/metabolismABSTRACT
Hsp27 and alphaB-crystallin are molecular chaperones that are constitutively expressed in several mammalian cells, particularly in pathological conditions. These proteins share functions as diverse as protection against toxicity mediated by aberrantly folded proteins or oxidative-inflammation conditions. In addition, these proteins share anti-apoptotic properties and are tumorigenic when expressed in cancer cells. This review summarizes the current knowledge about Hsp27 and alphaB-crystallin and the implications, either positive or deleterious, of these proteins in pathologies such as neurodegenerative diseases, myopathies, asthma, cataracts and cancers. Approaches towards therapeutic strategies aimed at modulating the expression and/or the activities of Hsp27 and alphaB-crystallin are presented.
