Science - USA (2021-12-24)

SCIENCE science.org 24 DECEMBER 2021 • VOL 374 ISSUE 6575 1574-B

RESEARCH

CORONAVIRUS

Vaccine breakthrough

infections

The vaccines developed
against severe acute respira-
tory syndrome coronavirus
2 (SARS-CoV-2) confer very
high protection against severe
COVID-19. However, as the
vaccine rollout has progressed
and variants have emerged,
it has become clear that
immune protection can wane
4 to 6 months after the second
immunization, especially in
older people and those who are
immunocompromised. With
vaccine breakthrough infections
increasing, particularly with the
prevalence of the Delta variant,
impressive responses have been
obtained from booster immuni-
zations. In a Perspective, Gupta
and Topol discuss the emergence
of breakthrough infections and
the need for booster doses to
improve immune protection.
Although boosters are important,
so are nonpharmacological inter-
ventions such as masking, which
help to reduce cases of COVID-19
and thereby limit the opportunity
for the emergence of variants
that can evade immunity. —GKA
Science, abl8487, this issue p. 1561

IMMUNOLOGY

Fibrin gums up the works
Plasmin is an abundant plasma
protease that cleaves and
deactivates the clot-associated
protein fibrin. Human deficien-
cies in plasmin and its inactive
proenzyme form, plasminogen
(PLG), cause severe inflamma-
tion in mucosal tissues such
as the mouth and eyes. Silva
et al. report that, like humans,
mice lacking plasminogen
accumulate extravascular fibrin
and develop an oral pathol-
ogy that phenocopies human
ligneous periodontitis (see the
Perspective by Vicanolo and
Hidalgo). The excess fibrin acti-
vates neutrophils through the
aMb2 (Mac-1) integrin receptor,
which triggers the production

of reactive oxygen species and

neutrophil extracellular traps.

Additionally, certain human

polymorphisms in the PLG gene

were found to be associated with

increased likelihood of develop-

ing periodontitis, suggesting that

fibrin–neutrophil interactions

may be an attractive target for

future treatments of this preva-

lent disease. —STS

Science, abl5450, this issue p. 1575;

see also abn0399, p. 1559

ENERGETICS

Efficiency leads to leisure

Humans are animals—merely

another lineage of great apes.

However, we have diverged in

significant ways from our ape

cousins and we are perennially

interested in how this happened.

Kraft et al. looked at energy

intake and expenditure in mod-

ern hunter-gatherer societies

and great apes. They found that

we do not spend less energy

while foraging or farming, but we

do acquire more energy and at a

faster rate than our ape cousins.

This difference may have allowed

our ancestors to spend more

time in contexts that facilitated

social learning and cultural

development. —SNV

Science, abf0130, this issue p. 1576

PLANT SCIENCE

Root meristem controls

The plant meristem, a small

cluster of stem cells, generates all

of the cell types necessary for the

plant’s indeterminate growth pat-

tern. Roszak et al. use single-cell

analyses to follow develop-

ment from the stem cell to the

enucleated cell of the phloem

vasculature. In the root of the

small mustard plant Arabidopsis,

this process takes just over 3

days, and the developmental tra-

jectory spans more than a dozen

different cell states. A transcrip-

tional program initially held under

repressive control is released

as those initial repressors dis-

sipate. Reciprocal repression by

regulators early and late in the

developmental trajectory control

a rapid switch in the differentia-

tion program. —PJH

Science, aba5531, this issue p. 1577

PALEONTOLOGY

Early marine giant

The largest animals to have

ever lived occupied the marine

environment. Modern cetaceans

evolved their large size over tens

of millions of years in response

to the increased productivity of

cold marine waters. However,

whales were not the first marine

giants to evolve. Sander et al.

describe a 244-million-year-old

fossil ichthyosaur that would

have rivaled modern cetaceans

in size (see the Perspective

by Delsett and Pyenson). The

animal existed at most 8 million

years after the emergence of the

first ichthyosaurs, suggesting a

much more rapid size expan-

sion that may have been fueled

by processes after the Permian

mass extinction. —SNV

Science, abf5787, this issue p. 1578;

see also abm3751, p. 1554

ULTRAFAST MAGNETISM

Coupling up of spins

and lattice

The development of spintronics

and magnetic data storage relies

on understanding and control-

ling the dynamics of magnetic

excitations within a material. Of

crucial importance for practi-

cal applications is how fast the

magnetization can be switched.

Mashkovich et al. report the use

of ultrafast terahertz radiation to

create magnon excitations in the

antiferromagnet cobalt difluo-

ride that can then be coupled

with phonon excitations (see the

Perspective by Juraschek and

Narang). Using light to control

coupling between the spins and

the lattice provides a route to

manipulating magnetization in

antiferromagnetic materials on

ultrafast time scales. —ISO

Science, abk1121, this issue p. 1608;

see also abm0085, p. 1555

BIOCATALYSIS

Radical cyclization

made easy

Metalloenzymes contain metal

cofactors that can sometimes be

exploited to catalyze reactions

distinct from their natural func-

tion. Drawing on inspiration from

heme-based radical polymer-

izations, Zhou et al. screened

a panel of metalloproteins for

candidates that could catalyze

an atom-transfer radical cycliza-

tion, producing a lactam from

an amide substrate bearing bro-

moalkyl and alkene functional

groups (see the Perspective by

Zhang and Dydio). Cytochrome

P-450 derivatives were effective

catalysts, and a series of enzyme

variants were generated by

directed evolution to access the

full range of enantiomer and dia-

stereomer products for model

substrates. Such biocatalysts

are valuable additions to the

synthetic chemistry toolkit and

reiterate the potential of metal-

loenzymes in catalyzing useful

unnatural reactions. —MAF

Science, abk1603, this issue p. 1612;

see also abm8321, p. 1558

CORONAVIRUS

How the Delta variant

evades defenses

In the course of the COVID-19

epidemic, variants of severe

acute respiratory syndrome

coronavirus 2 (SARS-CoV-2)

continue to emerge, some

of which evade immunity or

increase transmission. In late

2020, the Delta and Kappa

variants were detected, and the

Delta variant became glob-

ally dominant by June 2021.

McCallum et al. show that vac-

cine-elicited serum-neutralizing

activity is reduced against these

variants. Based on biochemis-

try and structural studies, the

authors show that mutations in

the domain that binds the ACE2

receptor abrogate binding to

some monoclonal antibodies but

do not improve ACE2 binding,

Edited by Michael Funk

ALSO IN SCIENCE JOURNALS