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SCIENCE sciencemag.org

RESEARCHEdited by Stella Hurtley

I N SC IENCE J O U R NA L S

GEOCHEMISTRY

Volcanoes find a new carbon platform The geological carbon cycle

assumes that carbon is emit-

ted by volcanic eruptions and

removed through various forms

of burial. Mason et al. found

that not all volcanic eruptions

have the same source for

carbon in their volcanic gas.

Arc volcanic activity appears

to harvest carbon from old

carbonate platforms, which

results in a massive difference

in the isotopic signature of the

carbon emitted during erup-

tion. This discovery requires

revision of the global carbon

cycle, decreasing the amount of

organic carbon believed to be

being buried. —BG

Science, this issue p. 290

MECHANOCHEMISTRY

Pulling on bonds counterintuitively Experimental mechanochem-

istry has largely focused on

the application of force along

chemical bonds to accelerate

their cleavage. Akbulatov et al.

now demonstrate that force

can also play a more subtle

role. They generated strained

macrocyclic rings photochemi-

cally and then studied the

influence of that strain on the

rates of reactions that cleaved

either phosphorus-oxygen or

silicon-oxygen bonds. P–O

cleavage was accelerated by

force orthogonal to the bond

axis, whereas the Si–O cleav-

age was inhibited by force along

the bond. Both results were

consistent with the respective

transition states predicted by

theory. —JSY


ANIMAL PHYSIOLOGY

Hydraulic fins The lymphatic system in fish

has much the same function as

it does in mammals—immune

response and homeostasis.

Pavlov et al. show, however,

that in the scromboid (tuna and

mackerel) family of fish, this

fluid homeostasis function has

been co-opted to help facilitate

dorsal fin rigidity and move-

ment (see the Perspective by

Triantafyllou). In bluefin tuna,

a series of lymphatic vessels

are integrated with muscles

that allow the fish to raise and

stiffen their dorsal fin. This

provides extra stability during

swimming. —SNV

Science, this issue p. 310;

see also p. 251

DNA REPLICATION

Getting loaded—make mine a double! Chromosomal DNA replication

initiates bidirectionally by load-

ing two ring-shaped helicases

onto DNA in opposite orienta-

tions. How this symmetry is

achieved has been puzzling

because replication initiation

ECONOMICS

Ecosystem protection payments pay off

Trees take up a lot of CO2, so one approach to reducing the rate of increase in atmospheric CO2

levels is to reduce the cutting down of trees. Jayachandran et al. evaluated a program in which

forest owners in Uganda were paid to not cut down their trees. Encouragingly, payments did

reduce deforestation, and owners did not compensate by cutting down trees in neighboring

forests. Furthermore, even in a scenario where cutting resumed after payments ceased, the

beneficial delay in CO2 release from cut trees, as quantified by the social cost of carbon, outweighed

the monetary cost. —GJC


Paying to protect

Ugandan forests

is worth the cost.

21 JULY 2017 • VOL 357 ISSUE 6348 263

Close-up view of the Hsp104 disaggregase Gates et al., p. 273

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QUANTUM COMPUTING

Making a quantum-classical hybridPredicting the dynamics of

many-body quantum systems

is a formidable computational

task, in which quantum comput-

ers could come to the aid of

classical ones. However, the

corrections needed to keep

errors in check as a quantum

computer works require enor-

mous quantum resources. Li

and Benjamin propose a hybrid

quantum-classical computer

based on variational principles.

In the proposed system, the

classical computer does most

of the work and “outsources” to

its quantum partner only very

specific tasks. This reduces the

number of operations that the

quantum partner needs to do,

allowing it to be less than per-

fect; the system can efficiently

compensate for the quantum

partner’s errors. A numerical

simulation of this hybrid system

compares it favorably with com-

peting methods. —JS

Phys. Rev. X 7, 021050 (2017).

CLIMATE CHANGE

Get ready, get set, get wetOne of the expected conse-

quences of anthropogenic

climate change is the intensifi-

cation of the hydrological cycle

as a result of higher surface

air temperatures. A commonly

invoked description of how

that will happen is “the dry

will get drier and the wet will

get wetter”—but exactly how

much wetter the wet regions

will get is difficult to predict.

Borodina et al. used spatially

aggregated observational data

of precipitation from 1951 to

2005 to calibrate model outputs

Edited by Caroline Ash

and Jesse Smith

sites contain only one essential

binding site for the initiator,

the origin recognition complex

(ORC). Coster and Diffley now

show that both helicases are

loaded by a similar mecha-

nism. Efficient loading requires

binding of two ORC complexes

to two ORC binding sites in

opposite orientations. Natural

origins were found to be par-

tially symmetrical, containing

functionally relevant second-

ary ORC sites. Sites can be

flexibly spaced, but introducing

an intervening “roadblock”

prevented loading, suggest-

ing that individual helicases

translocate toward each other

on DNA to form a stable double

ring. —SMH


SOFT ROBOTS

Reaching out as a way to growHumans normally think of

motion as a physical shifting

from one location to another.

But for some plants, such as

creeping vines, and even some

cells, such as neurons, motion

is accomplished by growth from

a present location toward a

desired one. Leveraging the flex-

ibility that is possible with soft

materials, Hawkes et al. used

pneumatics to lengthen the tip

of a robot over an extended dis-

tance. They inflated chambers

on only one side of the robot to

make it turn. An onboard cam-

era connected to a feedback

loop allowed the robot to track

toward a distant light source.

—MSL

Sci Robot. 10.1126/scirobotics.

aan3028 (2017).

NEUROREHABILITATION

Greater gait with gravityOften taken for granted,

gravity—the force that keeps

you on the ground—becomes a

notable challenge during reha-

bilitation from injury. Mignardot

et al. “harnessed” gravity,

using a robotic body weight–

supportive device to supply

upward and forward forces to

the torso to assist with locomo-

tion. Patients recovering from

stroke or spinal cord injury

demonstrated improved gait

performance with the robotic

harness. An algorithm was

developed to adjust the forces

provided by the robotic har-

ness according to the patient’s

needs. Nonambulatory patients

were able to walk naturally

with the harness, and ambula-

tory patients showed improved

balance, limb coordination,

foot placement, and steer-

ing. A clinical trial using this

robot-assistive rehabilitation

approach for patients with

spinal cord injury is now under

way. —CC

Sci. Transl. Med. 9, eaah3621 (2017).

BATTERIES

A stretchy binder protects the silicon A challenge in using silicon

particles for lithium batteries is

that the large volume changes

during charge-discharge

cycling cause the particles to

fracture, which builds up an

insulating interface layer. Choi

et al. show that traditional

binder materials used to cush-

ion the silicon particles can

be improved by adding small

amounts of polyrotaxanes (see

the Perspective by Ryu and

Park). The molecules consist of

multiple rings that are strung

along a linear segment and

stoppered at each end. Some

of the rings are anchored to the

polymer binder, whereas others

float freely, yielding a highly

mobile but connected net-

work that anchors the binder,

and thus the silicon particles,

together. —MSL


see also p. 250

Disintegrated silicon microparticles

IN OTHER JOURNALS

Parasitoid wasps

have evolved venoms

for host control.

RESEARCH | IN SCIENCE JOURNALS

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RESEARCH

CANCER

Cancer epigenetics in the driver’s seat Recent cancer genome projects

unexpectedly highlighted the

role of epigenetic alterations in

cancer development. About half

of human cancers were found to

harbor mutations in chromatin

proteins. In a Review, Flavahan et

al. propose that chromatin and

epigenetic aberrations have the

potential to confer on cells the

full range of oncogenic proper-

ties represented in the classic

“hallmarks” depiction of cancer.

They suggest that genetic,

environmental, and metabolic

factors can make chromatin

aberrantly permissive or restric-

tive. Permissive chromatin

creates a state of “epigenetic

plasticity,” which can activate

oncogene expression or cell

fate changes that drive cancer

development. —PAK


STRUCTURAL BIOLOGY

Untangling aggregates one step at a time Conserved AAA+ protein

complexes exploit adenosine

triphosphate hydrolysis to

unfold and disaggregate their

substrates in response to cell

stress, but exactly how they do

this has been unclear. Gates et

al. determined high-resolution

cryo–electron microscopy

structures of the Hsp104 disag-

gregase bound to an unfolded

polypeptide substrate in its

channel. The structures reveal

substrate interactions and two

different translocation states.

Hsp104 undergoes confor-

mational changes that drive

movement along the substrate

by two-amino-acid steps.

These states help explain how

this molecular machine can

solubilize protein aggregates and

amyloids. —SMH


ORGANIC CHEMISTRY

Lighting the way to carbon borylation Boron substituents provide

versatile reactivity, and their

utility has been emerging in

pharmaceutical contexts.

Fawcett et al. show that visible

light can induce replacement

of carboxylic acid groups with

boronate esters, which will ease

their introduction into a wide

variety of compounds. Once

the acids are activated with

phthalimide substituents, they

can react with catecholborane

dimers under illumination in

amide solvents, with no need for

catalysts or other additives. The

reaction appears to proceed by

radical chain propagation after

photoinitiation. —JSY


TOPOLOGICAL MATTER

A propagating Majorana mode Although Majorana fermions

remain elusive as elementary

particles, their solid-state analogs

have been observed in hybrid

semiconductor-superconductor

nanowires. In a nanowire setting,

the Majorana states are localized

at the ends of the wire. He et

al. built a two-dimensional

heterostructure in which a one-

dimensional Majorana mode is

predicted to run along the sample

edge (see the Perspective by

Pribiag). The heterostructure con-

sisted of a quantum anomalous

Hall insulator (QAHI) bar con-

tacted by a superconductor. The

authors used an external mag-

netic field as a “knob” to tune into

a regime where a Majorana mode

was propagating along the edge

of the QAHI bar covered by the

superconductor. A signature of

this propagation—half-quantized

conductance—was then observed

in transport experiments. —JS


see also p. 252

TOPOLOGICAL MATTER

Making a large-gap topological insulator Although of interest to basic

research, topological insulators

(TIs) have not yet lived up to

their technological potential.

This is partly because their

protected surface-edge state

usually lives within a narrow

energy gap, with its exotic trans-

port properties overwhelmed

by the ordinary bulk material.

Reis et al. show that a judicious

choice of materials can make the

gap wide enough for the topo-

logical properties to be apparent

at room temperature. Numerical

calculations indicate that a

monolayer of Bismuth grown on

SiC(0001) is a two-dimensional

TI with a large energy gap. The

researchers fabricated such a

heterostructure and character-

ized it using scanning tunneling

spectroscopy. The size of the

experimentally measured gap

was consistent with the calcula-

tions. —JS


NONLINEAR OPTICS

Hitting the highs in solid state The ability to generate high

harmonics of optical frequencies

through the nonlinear interac-

tion between intense light pulses

and gas atoms has opened

up the area of ultrafast optics

and spectroscopy. Sivis et al.

now show that high harmonics

can also be generated with a

solid-state sample. They used

nanofabricated structured

targets of ZnO and varied the

chemical composition of the

sample to demonstrate that

(modest) high harmonics can be

generated as the light interacts

with the target materials. The

results present the possibility of

developing solid-state ultrafast

optical devices. —ISO


PIEZOELECTRICS

Finding a more flexible mechanical sensor Piezoelectric materials allow

conversion between electric-

ity and mechanical stresses.

The most efficient piezoelectric

materials are ceramics such

as BaTiO3 or PbZrO

3, which are

also extremely stiff. You et al.

identified an organic perovskite

structured piezoelectric material

that is far more pliable yet has a

piezoelectric response similar to

that of traditional ceramics. This

material may be a better option

to use as a mechanical sensor

for flexible devices, soft robotics,

biomedical devices, and other

micromechanical applications

that benefit from a less stiff

piezoelectric material. —BG


GEOENGINEERING

Geoengineering for temperature controlAs global temperatures continue

to rise, potential large-scale

interventions in Earth’s climate

system to reduce global warming

are receiving increasing attention

(see the Editorial by Pasztor et

al.). In a Perspective, Niemeier

and Tilmes explore one such

geoengineering approach, strato-

spheric aerosol modification. This

approach would involve injecting

vast amounts of sulfur or other

aerosols into the stratosphere to

reduce the amount of solar light

reaching Earth’s surface. In a sec-

ond Perspective, Lohmann and

Gasparini explain a less known

geoengineering approach, cirrus

cloud seeding. This approach

aims to increase the amount

of longwave radiation leaving

Earth’s atmosphere. Although

these approaches might reduce

warming, they have many as yet

unpredictable side effects and

would not address problems such

as ocean acidification. —JFU

Science, this issue p. 231, p. 246;

see also p. 248

Edited by Stella HurtleyALSO IN SCIENCE JOURNALS

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NEURODEGENERATION

The amyloid connection in Parkinson’sParkinson’s disease is a progres-

sive neurodegenerative disorder

that is commonly associated

with activating mutations in

the kinase LRRK2. The disease

results in dementia owing to loss

of dopaminergic neurons. Chen

et al. discovered why activating

LRRK2 mutations are toxic to

neurons. When phosphorylated

by mutant LRRK2, a cleavage

product of amyloid precursor

protein (APP) translocated

to the nucleus and was more

transcriptionally active, which

killed the dopaminergic neurons.

These findings connect the

pathology of Parkinson’s to that

of Alzheimer’s disease, in which

dementia is associated with

another APP cleavage product,

β-amyloid. —LKF

Sci. Signal. 10, eaam6790 (2017).

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research - science...“hallmarks” depiction of cancer. they suggest that genetic, environmental,...

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