Science 13Mar2020

Moreover, removal of 54 amino acids from the
glutamine-rich region specifically interfered
with long-term, but not short-term, memory
(fig. S12B) ( 6 ).
Several structures of functional amyloids,
produced in vitro from truncated protein, have
been solved ( 29 , 30 ). By contrast, Orb2 filament
represents a biochemically active full-length
functional amyloid extracted from the endog-
enous source (fig. S13). The threefold symmetry
of the ordered core of Orb2 resembles that
ofb-amyloid1-40filaments seeded from Alz-
heimer’s disease brain tissue ( 31 )orassembled
in vitro ( 32 ). However, unlike the hydrophobic
b-amyloid1-40core, Orb2 forms a hydrophilic
core stabilized by interdigitated glutamines.
When Orb2 filaments were assembled from
recombinant protein, filaments were longer,
morphologically distinct, and less biochemically
active and had negligible seeding capacity com-
pared with endogenous ones under our exper-
imental conditions (fig. S14), suggesting that
thesameprion-likeproteincanadoptdistinct
structures in vitro and in vivo. Other proteins
with glutamine-richsequences are known
to produce amyloids ( 33 ). The interdigitated
cross-bstructure observed in Orb2 filaments
could be extended on both sides of a parallel
b-sheet made of only glutamine residues, which
would allow for the formation of stable, mul-
tilayered cross-bstructures from long poly-
glutamine sequences, such as in pathological
glutamine expansions.
There are a number of ways that“molecu-
lar memories”can be created: increase in the
amount of a protein, where the kinetics of
decay to the basal state would be the duration
of memory; a stable protein or protein state,
the half-life of which would inform the dura-
tion of memory ( 34 , 35 ); or a feed-forward
molecular circuit, whose activity could be
reciprocally perpetuated across time. A self-
sustaining amyloid formed by a single poly-
peptide uses all three mechanisms. The amyloid
fold itself is not“memory,”but the amyloid fold
reorganizes the rest of the Orb2 protein to create
a persistent alteration in the synthesis of specific
synaptic proteins. Memory is the altered syn-

aptic state that results from the change in

functional state of the Orb2 (fig. S13). How-

ever, amyloid formation is generally assumed

to be irreversible in physiological conditions;

then, how can memory be dynamic? Or is it

possible that some memories are irreversible

and appear lost merely because of an inability

to retrieve them? First, amyloids are not nec-

essarily irreversible and could exist in a dy-

namic equilibrium with the available monomer

( 36 ). Second, the Orb2 amyloid core is based

on a hydrophilic, glutamine- and histidine-rich

fold, and the protonation state of histidine

residues could influence Orb2 amyloid stabil-

ity. Lowering pH destabilized Orb2 filaments

(fig. S15), suggesting that functional amyloid

could be amenable to modification or even

dissolution. Our findings question the as-

sumption that amyloid formation in the brain

is always an unintended consequence that

leads to dysfunction. We postulate that the

brain fosters a cellular environment that is

permissive to the formation of an amyloid-

like state of certain proteins in order to meet

the diversity of functional requirements im-

posed on it.

REFERENCES AND NOTES

1. S. A. Josselyn, S. Tonegawa,Science 367 , eaaw4325 (2020).


2. G. Lynch, M. Baudry,Science 224 , 1057–1063 (1984).


3. F. Crick,Nature 312 , 101 (1984).


4. J. Shorter, S. Lindquist,Nat. Rev. Genet. 6 , 435–450 (2005).


5. L. Fioritiet al.,Neuron 86 , 1433–1448 (2015).


6. K. Keleman, S. Krüttner, M. Alenius, B. J. Dickson,
   Nat. Neurosci. 10 , 1587–1593 (2007).


7. S. Krüttneret al.,Neuron 76 , 383–395 (2012).


8. S. Krüttneret al.,Cell Rep. 11 , 1953–1965 (2015).


9. L. Liet al.,Curr. Biol. 26 ,3143–3156 (2016).


10. A. Majumdaret al.,Cell 148 , 515–529 (2012).


11. B. L. Raveendraet al.,Nat. Struct. Mol. Biol. 20 , 495– 501
    (2013).


12. J. S. Stephanet al.,Cell Rep. 11 , 1772–1785 (2015).


13. K. Si, Y. B. Choi, E. White-Grindley, A. Majumdar, E. R. Kandel,
    Cell 140 , 421–435 (2010).


14. K. Si, S. Lindquist, E. R. Kandel,Cell 115 , 879–891 (2003).


15. R. Herváset al.,PLOS Biol. 14 , e1002361 (2016).


16. V. Iglesiaset al.,Front.Physiol. 10 ,314 (2019).


17. R. Nelsonet al.,Nature 435 , 773–778 (2005).


18. R. Tycko,Neuron 86 , 632–645 (2015).


19. F. Chiti, C. M. Dobson,Annu. Rev. Biochem. 75 , 333– 366
    (2006).


20. H. Wu, M. Fuxreiter,Cell 165 , 1055–1066 (2016).


21. M. P. Hugheset al.,Science 359 , 698–701 (2018).


22. M. R. Khanet al.,Cell 163 , 1468–1483 (2015).
    23. H. A. Lashuel, D. Hartley, B. M. Petre, T. Walz,
    P. T. Lansbury Jr.,Nature 418 , 291 (2002).
    24. D. Perettiet al.,Nature 518 , 236–239 (2015).
    25. B. K. Stepienet al.,Proc. Natl. Acad. Sci. U.S.A. 113 ,
    E7030–E7038 (2016).
    26. T. Mastushita-Sakai, E. White-Grindley, J. Samuelson,
    C.Seidel,K.Si,Proc. Natl. Acad. Sci. U.S.A. 107 ,
    11987 – 11992 (2010).
    27. G. Didelotet al.,Science 313 , 851–853 (2006).
    28. J. Zivanovet al.,eLife 7 , e42166 (2018).
    29. C. Wasmeret al.,Science 319 , 1523–1526 (2008).
    30. M. Mompeánet al.,Cell 173 ,^1244 – 1253.e10(2018).
    31. J. X. Luet al.,Cell 154 , 1257–1268 (2013).
    32. A. K. Paravastu, R. D. Leapman, W. M. Yau, R. Tycko,
    Proc. Natl. Acad. Sci. U.S.A. 105 , 18349–18354 (2008).
    33. E. Scherzingeret al.,Cell 90 , 549–558 (1997).
    34. S. Heoet al.,Proc. Natl. Acad. Sci. U.S.A. 115 , E3827–E3836
    (2018).
    35. R. Y. Tsien,Proc. Natl. Acad. Sci. U.S.A. 110 , 12456– 12461
    (2013).
    36. W. Qiang, K. Kelley, R. Tycko,J. Am. Chem. Soc. 135 ,
    6860 – 6871 (2013).

ACKNOWLEDGMENTS

We thank D. Laurents, J. Oroz, W. Redwine, K. Patton, R. Halfmann,

and S. Garcia Alcantara for comments; M. Miller for illustrations;

C. Zhang, P. Leal, A. Machen, and A. Rodriguez Gama for

experimental assistance; A. Saraf for assistance in mass

spectrometry; K. Xi, F. Guo, and T. Parmely for support with

electron microscopy; and G. Murshudov and R. Warshamanage for

help with REFMAC. This work is dedicated to the memory of

Mark T. Fisher, Ph.D. (University of Kansas Medical Center).

Funding:This work was supported by the UK Medical Research

Council (MC_UP_A025_1013, to S.H.W.S.) and Stowers Institute for

Medical Research (to K.S).Author contributions:Conceptualization,

K.S. and R.H.; investigation, R.H., M.J.R., Y.P., W.Z., A.G.M., and

S.H.W.S.; resources, K.S, J.A.J.F., and S.H.W.S.; software, S.H.W.S.;

supervision, K.S.; writing, original draft, K.S. and R.H.; writing–

review and editing, all authors.Competing interests:The authors

declare no competing financial interests.Data and materials

availability:Cryo-EM density map for Orb2 has been deposited

in the Electron Microscopy Data Bank (EMDB) under accession

no. EMD-21316. Refined atomic model has been deposited in the

Protein Data Bank (PDB) under accession no. 6VPS. The mass

spectrometry data have been deposited to the ProteomeXchange

Consortium (http://proteomecentral.proteomexchange.org) by

way of the MassIVE repository with the dataset identifier

PXD016266. Original data underlying this manuscript can be

accessed from the Stowers Original Data Repository at

http://www.stowers.org/research/publications/LIBPB-1486.

SUPPLEMENTARY MATERIALS

science.sciencemag.org/content/367/6483/1230/suppl/DC1

Materials and Methods

Figs. S1 to S15

Table S1

References ( 37 – 53 )

View/request a protocol for this paper fromBio-protocol.

25 November 2019; accepted 18 February 2020

10.1126/science.aba3526

Hervaset al.,Science 367 , 1230–1234 (2020) 13 March 2020 5of5

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