50-fold higher ATP/ADP ratio is necessary to
fuel the myriad metabolic reactions taking place
simultaneously in a cell. However, cytoplasm can
have protein concentrations over 100 mg/mL
(31–33), and it is extremely difficult to maintain
such high protein concentrations in a test tube
without spontaneous aggregation. The hydrotrope activity of ATP may help keep proteins soluble in the cytoplasm (34) and provide another,
but not mutually exclusive, explanation for high
ATP concentrations in cells. Possibly also, as the
levels of ATP decline with age or mitochondrial
impairment, this could lead to increased aggregation and consequently neurodegenerative decline during aging. Our work in this paper has
focused on the role of ATP in keeping unstructured proteins soluble, because these are the
types of proteins that have a propensity to form
pathological aggregates (35). It will be interesting
to examine the role of high ATP concentrations in
stability and function of multimolecular protein
More generally, during evolution, the production of complex macromolecules would have immediately presented the problem of aggregation.
As one of the basic building blocks in RNA and
DNA, ATP may have been coopted early in evolution to prevent such aggregation. It is ideal for
this purpose, due to the high activation energy required to hydrolyze the polyphosphate bonds in
an ATP-Mg-water complex. ATP could later have
been adopted to provide the basic energy source
for metabolism, which is the hydrolysis of ATP
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We particularly thank W. Kunz and colleagues for their help,
support, advice, and discussions during the preparation of
the manuscript. We thank D. Drechsel, A. Nadler, K. Sandhoff,
D. Tang, and members of the Hyman, Krishnan, and Alberti
laboratories for helpful discussions; B. Bogdanovo and
R. Lemaitre for help with protein expression and purification;
B. Lombardot and R. Hasse from the Scientific Computing
facility for image analysis; and B. Nitzsche and B. Schroth-Diez
for help with light microscopy. We gratefully acknowledge
funding from the Alexander von Humboldt Foundation (GRO/
1156614 STP-2 to A.P. and USA/1153678 STP to S.S.), EMBO
ALTF (608-2013 to S.S.), and German Federal Ministry of
Research and Education (BMBF 031A359A Max Syn Bio). Y.K.
acknowledges the Scientific Innovation Award from the Brain
Research Foundation (BRF SIA-2016-01) and start-up funds
from the University of Chicago. A.A.H. and A.P. are inventors on
patent application 1305-5403-MSG-ZE, submitted by the Max
Planck Society, which covers nucleotides as hydrotropes.
Materials and Methods
Figs. S1 to S4
14 March 2016; accepted 24 March 2017
756 19 MAY 2017 • VOL 356 ISSUE 6339 sciencemag.org SCIENCE
Fig. 4. ATP enhances protein stability. (A) Heat denaturation of crude egg white can be
inhibited by addition of ATP-Mg. Crude egg white was heated at 60°C in a water bath in the
presence of equimolar (10 mM) amounts of ATP-Mg, nonhydrolysable APPCP-Mg, and NaXS.
NaCl (40 mM) was used to match the ionic strength of ATP-Mg. Over 30 min, the aggregation
of egg white is abolished in the presence of ATP-Mg and APPCP-Mg. (B) The stabilization of
heat-denatured egg white is concentration dependent. The kinetic traces of egg-white
aggregation [conditions as in (A)] in the presence of increasing concentrations of ATP-Mg
over 60 min. The amount of egg-white aggregation is assessed by changes of the pixel value
(integrated density). Four mM of ATP-Mg blocked aggregation by 50%, whereas 12 mM of
ATP-Mg completely abolished aggregation. The shaded area represents the range of the
standard error (n = 3). (C) The dose response for stabilization of heat-denatured egg white. The
amount of egg-white aggregation was assessed by turbidity measurement in a 96-well plate.
The aggregation of egg white decreases with increasing concentrations. Lines represent fitted
dose-response curves [log(concentration versus aggregated material assessed by turbidity
measurement]. Error bars, mean ± SD (N = 3). The range of concentrations of all added reagents
was adjusted to match the range of ionic strength of ATP-Mg (see the supplementary materials