Each year more than 250,000 infants in the United States are exposed to artificial lighting in hospital nurseries with little consideration given to environmental lighting cycles. Essential in determining whether environmental lighting cycles need to be considered in hospital nurseries is identifying when the infant’s endogenous circadian clock becomes responsive to light. Using a non-human primate model of the developing human, we examined when the circadian clock, located in the hypothalamic suprachiasmatic nuclei (SCN), becomes responsive to light. Preterm infant baboons of different ages were exposed to light (5,000 lux) at night, and then changes in SCN metabolic activity and gene expression were assessed. After exposure to bright light at night, robust increases in SCN metabolic activity and gene expression were seen at ages that were equivalent to human infants at 24 weeks after conception. These data provide direct evidence that the biological clock of very premature primate infants is responsive to light.
The FixL proteins are biological oxygen sensors that restrict the expression of specific genes to hypoxic conditions. FixL’s oxygen-detecting domain is a heme binding region that controls the activity of an attached histidine kinase. The FixL switch is regulated by binding of oxygen and other strong-field ligands. In the absence of bound ligand, the heme domain permits kinase activity. In the presence of bound ligand, this domain turns off kinase activity. Comparison of the structures of two forms of the Bradyrhizobium japonicum FixL heme domain, one in the “on” state without bound ligand and one in the “off” state with bound cyanide, reveals a mechanism of regulation by a heme that is distinct from the classical hemoglobin models. The close structural resemblance of the FixL heme domain to the photoactive yellow protein confirms the existence of a PAS structural motif but reveals the presence of an alternative regulatory gateway.
The presence of magnetite crystal chains, considered missing
evidence for the biological origin of magnetite in ALH84001
[Thomas-Keprta, K. L., Bazylinski, D. A., Kirschvink,
J. L., Clemett, S. J., McKay, D. S., Wentworth, S.
J., Vali, H., Gibson, E. K., Jr., & Romanek, C. S. (2000)
Geochim. Cosmochim. Acta 64, 4049–4081], is
demonstrated by high-power stereo backscattered scanning electron
microscopy. Five characteristics of such chains (uniform crystal size
and shape within chains, gaps between crystals, orientation of
elongated crystals along the chain axis, flexibility of chains, and a
halo that is a possible remnant of a membrane around chains), observed
or inferred to be present in magnetotactic bacteria but incompatible
with a nonbiological origin, are shown to be present. Although it is
unlikely that magnetotactic bacteria were ever alive in ALH84001,
decomposed remains of such organisms could have been deposited in
cracks in the rock while it was still on the surface on Mars.
IL-18 can be considered a proinflammatory cytokine mediating
disease as well as an immunostimulatory cytokine that is important for
host defense against infection and cancer. The high-affinity,
constitutively expressed, and circulating IL-18 binding protein
(IL-18BP), which competes with cell surface receptors for IL-18 and
neutralizes IL-18 activity, may act as a natural antiinflammatory as
well as immunosuppressive molecule. In the present studies, the IL-18
precursor caspase-1 cleavage site was changed to a factor Xa site, and,
after expression in Escherichia coli, mature IL-18 was
generated by factor Xa cleavage. Mature IL-18 generated by factor Xa
cleavage was fully active. Single point mutations in the mature IL-18
peptide were made, and the biological activities of the wild-type (WT)
IL-18 were compared with those of the mutants. Mutants E42A and K89A
exhibited 2-fold increased activity compared with WT IL-18. A double
mutant, E42A plus K89A, exhibited 4-fold greater activity.
Unexpectedly, IL-18BP failed to neutralize the double mutant E42A plus
K89A compared with WT IL-18. The K89A mutant was intermediate in being
neutralized by IL-18BP, whereas neutralization of the E42A mutant was
comparable to that in the WT IL-18. The identification of E42 and K89
in the mature IL-18 peptide is consistent with previous modeling
studies of IL-18 binding to IL-18BP and explains the unusually high
affinity of IL-18BP for IL-18.
Light microscopy of thick biological samples, such as tissues, is
often limited by aberrations caused by refractive index variations
within the sample itself. This problem is particularly severe for live
imaging, a field of great current excitement due to the development of
inherently fluorescent proteins. We describe a method of removing such
aberrations computationally by mapping the refractive index of the
sample using differential interference contrast microscopy, modeling
the aberrations by ray tracing through this index map, and using
space-variant deconvolution to remove aberrations. This approach will
open possibilities to study weakly labeled molecules in
difficult-to-image live specimens.
The atomic force microscope (AFM) is a powerful tool for imaging individual biological molecules attached to a substrate and placed in aqueous solution. At present, however, it is limited by the speed at which it can successively record highly resolved images. We sought to increase markedly the scan speed of the AFM, so that in the future it can be used to study the dynamic behavior of biomolecules. For this purpose, we have developed a high-speed scanner, free of resonant vibrations up to 60 kHz, small cantilevers with high resonance frequencies (450–650 kHz) and small spring constants (150–280 pN/nm), an objective-lens type of deflection detection device, and several electronic devices of wide bandwidth. Integration of these various devices has produced an AFM that can capture a 100 × 100 pixel2 image within 80 ms and therefore can generate a movie consisting of many successive images (80-ms intervals) of a sample in aqueous solution. This is demonstrated by imaging myosin V molecules moving on mica (see http://www.s.kanazawa-u.ac.jp/phys/biophys/bmv_movie.htm).
Magnetic relaxation has been used extensively to study and characterize biological tissues. In particular, spin-lattice relaxation in the rotating frame (T1ρ) of water in protein solutions has been demonstrated to be sensitive to macromolecular weight and composition. However, the nature of the contribution from low frequency processes to water relaxation remains unclear. We have examined this problem by studying the water T1ρ dispersion in peptide solutions (14N- and 15N-labeled), glycosaminoglycan solutions, and samples of bovine articular cartilage before and after proteoglycan degradation. We find in model systems and tissue that hydrogen exchange from NH and OH groups to water dominates the low frequency water T1ρ dispersion, in the context of the model used to interpret the relaxation data. Further, low frequency dispersion changes are correlated with loss of proteoglycan from the extra-cellular matrix of articular cartilage. This finding has significance for the noninvasive detection of matrix degradation.
Degeneracy, the ability of elements that are structurally different to perform the same function or yield the same output, is a well known characteristic of the genetic code and immune systems. Here, we point out that degeneracy is a ubiquitous biological property and argue that it is a feature of complexity at genetic, cellular, system, and population levels. Furthermore, it is both necessary for, and an inevitable outcome of, natural selection.
Endothelial cells in most vascular beds release a factor that hyperpolarizes the underlying smooth muscle, produces vasodilatation, and plays a fundamental role in the regulation of local blood flow and systemic blood pressure. The identity of this endothelium-derived hyperpolarizing factor (EDHF), which is neither NO nor prostacyclin, remains obscure. Herein, we demonstrate that in mesenteric resistance arteries, release of C-type natriuretic peptide (CNP) accounts for the biological activity of EDHF. Both produce identical smooth muscle hyperpolarizations that are attenuated in the presence of high [K+], the Gi G protein (Gi) inhibitor pertussis toxin, the G protein-gated inwardly rectifying K+ channel inhibitor tertiapin, and a combination of Ba2+ (inwardly rectifying K+ channel blocker) plus ouabain (Na+/K+-ATPase inhibitor). Responses to EDHF and CNP are unaffected by the natriuretic peptide receptor (NPR)-A/B antagonist HS-142-1, but mimicked by the selective NPR-C agonist, cANF4–23. EDHF-dependent relaxation is concomitant with liberation of endothelial CNP; in the presence of the myoendothelial gap-junction inhibitor 18α-glycyrrhetinic acid or after endothelial denudation, CNP release and EDHF responses are profoundly suppressed. These data demonstrate that acetylcholine-evoked release of endothelial CNP activates NPR-C on vascular smooth muscle that via a Gi coupling promotes Ba2+/ouabain-sensitive hyperpolarization. Thus...