INSIGHTS | PERSPECTIVES
By Gregory M. Cook1,2 and Robert K. Poole3
Most biological oxygen consump- tion is carried out by membrane- integrated oxidases, which fall into three main classes. The heme-cop- per oxidases (HCOs) of mitochon- dria and many bacteria (1) have a
binuclear active site that contains a heme
and a copper atom. They achieve rapid, virtually complete reduction of oxygen to water. The alternative oxidases (AOXs) found
in certain plants, fungi, and bacteria have
a heme-free iron-iron reactive site (2) that
confers nitric oxide–resistant respiration
(3). The last class, the bacterial cytochrome
bd–type oxidases (4), are found in many
pathogenic bacteria and have a distinctive
heme composition consisting of two hemes
b and one heme d. On page 583 of this issue,
Safarian et al. report the atomic-resolution
structure of a cytochrome bd–type oxidase
from Geobacillus thermodenitrificans (5).
The structure will facilitate targeted and
rational drug development against cytochrome bd–type oxidases.
The unique spectral signatures of heme d
have made identification of cytochrome bd–
type oxidases in numerous types of bacteria
straightforward. Indeed, such an oxidase
was first described in the 1930s (6). They
have extraordinary ligand-binding activities: Respiration via cytochrome bd exhibits nanomolar afnity for oxygen (7), even
though oxygen can form a uniquely stable
oxygenated complex (8) that is the first intermediate in the accepted oxygen reduction
mechanism (4). Cytochrome bd also plays
special roles in pathogenic bacteria (9). For
The structure of an
oxidase found in many
pathogens will help
in drug development
1Department of Microbiology and Immunology, Otago School
of Medical Sciences, University of Otago, Dunedin 9054, New
Zealand. 2Maurice Wilkins Centre for Molecular Biodiscovery,
University of Auckland, Auckland 1042, New Zealand.
3Department of Molecular Biology and Biotechnology,
University of Shefeld, Shefeld S10 2 TN, UK.
pharmacologically with tetrodotoxin. Thus,
the shift in [K+]e is not the consequence of
local changes in synaptic activity.
In mice, wakefulness defined by electrical activity also was linked to increased
[K+]e, whereas natural sleep and anesthesia were associated with decreased
[K+]e. These sleep-wake–associated changes
in [K+]e were accompanied by inverse shifts
in extracellular calcium ([Ca2+]e), magnesium
([Mg2+]e), and hydrogen ([H+]e) ion concentrations, as well as extracellular space volume (see the figure).
Can simple alterations in the extracellu-
lar ion composition wake a sleeping animal
and put an awake animal to sleep? Ding et
al. formulated sleep-inducing and wake-
inducing artificial CSFs with ion concentra-
tions that mimicked those during natural
sleep or wakefulness, and examined how
these solutions afect neuronal activity and
extracellular space volume in mice. Cranial
windows were implanted in the left and
right cortices, allowing the infusion of ar-
tificial CSF into one neural hemisphere and
direct comparison with the contralateral
hemisphere. Remarkably, directed local
and brainwide manipulations of extracel-
lular ions can control neuronal activity and
extracellular volume, and can even over-
ride the overarching behavioral state. Thus,
extracellular ions contribute to the state-
dependent control of neuronal activity
across sleep and wakefulness.
Whether changes in the brain’s ionic
milieu control enhanced sleep drive after
prolonged wakefulness, and/or sleep satiation after extended recovery sleep, is not
known. It is also unclear whether regional
ionic shifts explain local sleep—that is, neuronal down states in one cortical area but
not in another. Pumps and transporters
that control ion flow across cell membranes
may be promising new targets for treating
sleep-wake disorders. Future work may also
assess the efects of REM sleep on extracellular ions, a sleep state characterized by
neurophysiological features that are common to both sleep and wakefulness (11). j
1. F. Ding et al ., Science352, 550 (2016).
2. R. E. Brown etal ., Physiol.Re v.92, 1087 (2012).
3. I. Timofeev et al., Proc. Natl. Acad. Sci. U.S.A. 98,1924
4. Y. Nir et al., Neuron70, 153 (2011).
5. S. C. Holst et al ., J. Neurosci.34, 566 (2014).
6. J. H. Benington, H. C. Heller, Prog. Neurobiol. 45, 347
7. J. Seigneur etal ., Cereb.Cortex 16, 655 (2006).
8. N. Kleitman, in Sleep and Wakefulness, N. Kleitman, Ed.
(Univ. of Chicago Press, Chicago, IL, 1963), pp. 195–207.
9. V. Demole, Naunyn Schmiedebergs Arch. Pharmacol. 120,
10. M. Cloëtta et al ., Naunyn Schmiedebergs Arch. Pharmacol.
174, 589 (1934).
11. G. Tinguely etal.,NeuroImage 32, 283 (2006).
transitions are accompanied
by changes in extracellular
space volume and concentration
of extracellular ions
and brain stem
Ionic milieu of sleep. Wakefulness and slow-wave sleep difer markedly in polysomnographic signals (EEG,
electroencephalogram), brain neuromodulator activity, extracellular ion concentrations, and interstitial volume.