Skip to main page content
U.S. flag
See More

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2014 May 27:3:e02218.
doi: 10.7554/eLife.02218.

Hsp70 chaperones are non-equilibrium machines that achieve ultra-affinity by energy consumption

Paolo De Los Rios  1 , Alessandro Barducci  2
Affiliations

Hsp70 chaperones are non-equilibrium machines that achieve ultra-affinity by energy consumption

Paolo De Los Rios et al. Elife. .

Abstract

70-kDa Heat shock proteins are ATP-driven molecular chaperones that perform a myriad of essential cellular tasks. Although structural and biochemical studies have shed some light on their functional mechanism, the fundamental issue of the role of energy consumption, due to ATP-hydrolysis, has remained unaddressed. Here we establish a clear connection between the non-equilibrium nature of Hsp70, due to ATP hydrolysis, and the determining feature of its function, namely its high affinity for its substrates. Energy consumption can indeed decrease the dissociation constant of the chaperone-substrate complex by several orders of magnitude with respect to an equilibrium scenario. We find that the biochemical requirements for observing such ultra-affinity coincide with the physiological conditions in the cell. Our results rationalize several experimental observations and pave the way for further analysis of non-equilibrium effects underlying chaperone functions.DOI: http://dx.doi.org/10.7554/eLife.02218.001.

Keywords: chaperones; dissociation constant; non-equilibrium.

PubMed Disclaimer

Conflict of interest statement

The authors declare that no competing interests exist.

Figures

Figure 1.
Figure 1.. Canonical Hsp70 biochemical cycle.
The model takes into account four states in Hsp70 (NBD is schematically represented here in green, SBD in orange), which are defined by substrate binding and by the nature of the bound nucleotide (ADP or ATP). The rates of the substrate binding/unbinding process (horizontal blue lines) are influenced by the nucleotide (kATPon, kATPoff, kATPon, kATPoff). ADP-bound states are converted to ATP-bound states through a nucleotide exchange process (vertical solid blue lines) with rates kDT , kDTS. The ATP to ADP conversion can occur by means of either a nucleotide exchange process (dashed blue lines) with rates kTDex, kTDex,S or ATP-hydrolysis (red lines) with rates kh, khS. DOI: http://dx.doi.org/10.7554/eLife.02218.003
Figure 2.
Figure 2.. Effect of ATP-hydrolysis on Keffneq.
Total energy consumption (A) and effective non-equilibrium dissociation constant of the Hsp70-substrate complex (B) is plotted as a function of the hydrolysis acceleration ratio khs/kh, for the DnaK/DnaJ/substrate system with concentrations [Hsp70]tot = 40 μM and [S]tot = 4 μM (see ‘Materials and methods’ for the parameters), The approximate dissociation constant Keff,0neq is also plotted for comparison (black dashed line). The green region comprised between KD(ATP) and KD(ADP) corresponds to the range of affinities accessible at equilibrium (no hydrolysis). The red-to-yellow region corresponds to the values of the dissociation constants that are exclusively accessible to the non-equilibrium regime. The region where red fades to yellow (103 ≤ khs/kh ≤ 104) corresponds to the transition from physiological to non-physiological values of hydrolysis acceleration. DOI: http://dx.doi.org/10.7554/eLife.02218.004
Figure 3.
Figure 3.. Dependence of Keffneq on time-scale separation and on stoichiometric ratio.
(A) Non-equilibrium dissociation constant as a function of the hydrolysis acceleration ratio khs/kh and of the time-scale separation between the ATP- and ADP-state, expressed as the ratio between the substrate unbinding rates between the ATP- and ADP-state. (B) Non-equilibrium dissociation constant as a function of the hydrolysis acceleration ratio khs/kh and of the stoichiometric ratio between the total substrate and Hsp70 concentrations. The color codes are the same as in Figure 2, green for the region accessible in equilibrium, and red-to-yellow for the region accessible in non-equilibrium. The blue line is the non-equilibrium dissociation constant reported in Figure 2B. DOI: http://dx.doi.org/10.7554/eLife.02218.006
See this image and copyright information in PMC

References

    1. Böcking T, Aguet F, Harrison SC, Kirchhausen T. 2011. Single-molecule analysis of a molecular disassemblase reveals the mechanism of Hsc70-driven clathrin uncoating. Nature Structural & Molecular Biology 18:295–301. doi: 10.1038/nsmb.1985 - DOI - PMC - PubMed
    1. Bukau B, Weissman J, Horwich A. 2006. Molecular chaperones and protein quality control. Cell 125:443–451. doi: 10.1016/j.cell.2006.04.014 - DOI - PubMed
    1. Finka A, Goloubinoff P. 2013. Proteomic data from human cell cultures refine mechanisms of chaperone-mediated protein homeostasis. Cell Stress & Chaperones 18:591–605. doi: 10.1007/s12192-013-0413-3 - DOI - PMC - PubMed
    1. Gassler CS, WSiederkehr T, Brehmer D, Bukau B, Mayer MP. 2001. Bag-1M accelerates nucleotide release for human Hsc70 and Hsp70 and can act concentration-dependent as positive and negative cofactor. The Journal of Biological Chemistry 276:32538–32544. doi: 10.1074/jbc.M105328200 - DOI - PubMed
    1. Ge H, Qian M, Qian H. 2012. Stochastic theory of nonequilibrium steady states. Part II: applications in chemical biophysics. Physics Reports-Review Section Of Physics Letters 510:87–118

Publication types

MeSH terms

LinkOut - more resources