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- S. A. Josselyn, S. Tonegawa,Science 367 , eaaw4325 (2020).
- G. Lynch, M. Baudry,Science 224 , 1057–1063 (1984).
- F. Crick,Nature 312 , 101 (1984).
- J. Shorter, S. Lindquist,Nat. Rev. Genet. 6 , 435–450 (2005).
- L. Fioritiet al.,Neuron 86 , 1433–1448 (2015).
- K. Keleman, S. Krüttner, M. Alenius, B. J. Dickson,
Nat. Neurosci. 10 , 1587–1593 (2007). - S. Krüttneret al.,Neuron 76 , 383–395 (2012).
- S. Krüttneret al.,Cell Rep. 11 , 1953–1965 (2015).
- L. Liet al.,Curr. Biol. 26 ,3143–3156 (2016).
- A. Majumdaret al.,Cell 148 , 515–529 (2012).
- B. L. Raveendraet al.,Nat. Struct. Mol. Biol. 20 , 495– 501
(2013). - J. S. Stephanet al.,Cell Rep. 11 , 1772–1785 (2015).
- K. Si, Y. B. Choi, E. White-Grindley, A. Majumdar, E. R. Kandel,
Cell 140 , 421–435 (2010). - K. Si, S. Lindquist, E. R. Kandel,Cell 115 , 879–891 (2003).
- R. Herváset al.,PLOS Biol. 14 , e1002361 (2016).
- V. Iglesiaset al.,Front.Physiol. 10 ,314 (2019).
- R. Nelsonet al.,Nature 435 , 773–778 (2005).
- R. Tycko,Neuron 86 , 632–645 (2015).
- F. Chiti, C. M. Dobson,Annu. Rev. Biochem. 75 , 333– 366
(2006). - H. Wu, M. Fuxreiter,Cell 165 , 1055–1066 (2016).
- M. P. Hugheset al.,Science 359 , 698–701 (2018).
- 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.aba3526Hervaset al.,Science 367 , 1230–1234 (2020) 13 March 2020 5of5
RESEARCH | REPORT