Abstract
It has been established that Hsp60 can accumulate in the cytosol in various pathological conditions, including cancer and chronic inflammatory diseases. Part or all of the cytosolic Hsp60 could be naïve, namely, bear the mitochondrial import signal (MIS), but neither the structure nor the in solution oligomeric organization of this cytosolic molecule has still been elucidated. Here we present a detailed study of the structure and self-organization of naïve cytosolic Hsp60 in solution. Results were obtained by different biophysical methods (light and X ray scattering, single molecule spectroscopy and hydrodynamics) that all together allowed us to assay a wide range of concentrations of Hsp60. We found that Naïve Hsp60 in aqueous solution is assembled in very stable heptamers and tetradecamers at all concentrations assayed, without any trace of monomer presence.
Highlights
Hsp60 is a molecular chaperone, highly conserved during evolution that assists protein folding in mitochondria [1,2]
To gain insight into the naıve Hsp60 oligomeric structure, we investigated the protein properties and multimeric self-assembly equilibria by High Performance Liquid Chromatography (HPLC), dynamic and static light scattering (DLS and SLS, respectively), and blue native PAGE
The purpose of our work was to determine the structural arrangement in solution of naıve Hsp60, i.e., whether it forms heptamers and tetradecamers as mtHsp60 and GroEL do, and the impact of protein concentration on oligomer stability
Summary
Hsp is a molecular chaperone, highly conserved during evolution that assists protein folding in mitochondria [1,2]. It is encoded and transcribed by a nuclear gene and translated in the cytosol. The mitochondrial import of Hsp, to that of other protein precursors, is a complex mechanism that depends on the mitochondrial membrane potential, and involves several molecular chaperones, such as Hsp, in the matrix space [5,6] as well as in the cytosol [7,8]. Once Hsp is imported into mitochondria, its folding and self-assembly from monomers to oligomeric species is mediated by functional pre-existing Hsp complexes that catalyse chaperonin folding in an ATP-dependent process [9]
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