Understanding membrane protein structure by design

In contrast to soluble proteins, the primary interactions that specify and stabilize membrane protein structures are still largely a matter of speculation. Although van der Waals interactions have been gaining increasing favor as the dominant player, new results demonstrate the strength of hydrogen bonding in a membrane environment.     

Activation of innate defense against a paramyxovirus is mediated by RIG-I and TLR7 and TLR8 in a cell-type-specific manner

Recognition of pathogens by the innate immune system is mediated by pattern recognition receptors (PRRs), which recognize specific molecular structures of the infectious agents and subsequently trigger expression of genes involved in host defense. Toll-like receptors (TLRs) represent a well-characterized class of membrane-bound PRRs, and the RNA helicase retinoic acid inducible gene I (RIG-I) has recently been described as a novel cytoplasmic PRR recognizing double-stranded RNA (dsRNA). Here we show that activation of signal transduction and induction of cytokine expression by the paramyxovirus Sendai virus is dependent on virus replication and involves PRRs in a cell-type-dependent manner. While nonimmune cells relied entirely on recognition of dsRNA through RIG-I for activation of an antiviral response, myeloid cells utilized both the single-stranded RNA sensing TLR7 and TLR8 and dsRNA-dependent mechanisms independent of RIG-I, TLR3, and dsRNA-activated protein kinase R to trigger this response. Therefore, there appears to be a large degree of cell-type specificity in the mechanisms used by the host to recognize infecting viruses.     

Differences in the skin peptides of the male and female Australian tree frog Litoria splendida. The discovery of the aquatic male sex pheromone splendipherin, together with phe8 caerulein and a new antibiotic peptide caerin 1.10.

The skin secretions of female and male Litoria splendida have been monitored monthly over a three-year period using HPLC and electrospray mass spectrometry. Two minor peptides are present only in the skin secretion of the male. The first of these is the female-attracting aquatic male sex pheromone that we have named splendipherin, a 25 amino acid peptide (GLVSSIGKALGGLLADVVKSKGQPA-OH). This pheromone constitutes about 1% of the total skin peptides during the breeding season (January to March), dropping to about 0.1% during the period June to November. Splendipherin attracts the female in water at a concentration of 10-11-10-9 M, and is species specific. The second peptide is a wide-spectrum antibiotic of the caerin 1 group, a 25 residue peptide (GLLSVLGSVAKHVLPHVVPVIAEKL-NH2) named caerin 1.10. The neuropeptides of L. splendida are also seasonally variable, the change identical for both the female and male. During the period October to March, the sole neuropeptide present in skin secretions is caerulein [pEQDY(SO3)TGWMDF-NH2]; this is active on smooth muscle and is also an analgaesic. During the southern winter (June to September), more than half of the caerulein is hydrolysed to [pEQDYTGWMDF-NH2], a peptide that shows no smooth muscle activity. In place of caerulein, a new peptide, Phe8 caerulein [pEQDY(SO3)TGWFDF-NH2], becomes a major component of the skin secretion. Perhaps this seasonal change is involved in thermoregulation, that is, with the initiation and maintenance of the inactive (hibernation) phase of the animal.     

A 31P NMR study of the interaction of amphibian antimicrobialpeptides with the membranes of live bacteria

Summary Amphibian skin is a rich source of peptides that are specific to pathogens and act by disrupting bacterial membranes. Three antimicrobial peptides were isolated from the skin glands of Australian tree frogs,Litoria caerulea andLitoria genimaculata. NMR spectroscopy was used to observe changes induced by these peptides in the³¹P resonances of bacterial membranes in vivo. Caerin 1.1 and maculatin 1.1, both wide-spectrum antibiotics disrupted the membranes ofBacillus cereus andStaphylococcus epidermidis (Gram-positive), leading to an increase in the isotropic³¹P NMR signal. Caerin 4.1, a narrow-spectrum antibiotic, however, did not affect the³¹P spectra of these organisms. The results demonstrate the use of³¹P NMR to study the effects of membrane-disrupting agents on the membranes of live bacteria.     

Pneumonia in renal transplant patients.

Between January 1976 and March 1982, 28 episodes of pneumonia occurred in 26 renal transplant patients. The overall mortality rate was 46%. Of the 16 patients with nosocomial pneumonia 9 (56%) died, whereas of the 12 patients with community-acquired pneumonia 4 (33%) died. In all 9 cases of unknown cause the response to empiric treatment was prompt, whereas in 4 of the 10 cases of monomicrobial pneumonia and 8 of the 9 cases of polymicrobial pneumonia the patient died. Cytomegalovirus was the sole cause of the pneumonia in two patients and a contributing cause, along with aerobic gram-negative bacteria, in another five, four of whom also had a fungal infection. Two patients, both of whom survived, had nosocomial Legionnaires'' disease.     

Cranial morphological variation in Peromyscus maniculatus over nearly a century of environmental change in three areas of California

Determining how species respond to prolonged environmental change is critical to understanding both their evolutionary biology and their conservation needs. In general, organisms can respond to changing environmental conditions by moving, by adapting in situ, or by going locally or globally extinct. Morphological changes, whether plastic or adaptive, are one way that species may respond in situ to local environmental change. Because cranial morphology is influenced by selective pressures arising from an organism's abiotic and biotic environments, including aspects of thermal physiology, diet, and sensory ecology, studies of cranial morphology may generate important insights into how species are responding to environmental change. To assess potential response of deer mice (Peromyscus maniculatus) to changing conditions in the Sierra Nevada Mountains of California, we quantified cranial variation in museum specimens of this species collected approximately 100 years apart. Specifically, we examined how cranial morphology varies in three populations of this geographically widespread, ecological generalist over elevation and time. Our analyses indicate that cranial morphology does not differ with elevation within either modern or historical samples but does vary between time periods, suggesting that in situ responses to environmental change have occurred. Contrary to predictions based on Bergmann's rule, we found no consistent relationship between body size and either elevation or time, suggesting that morphological differences detected between historic and modern specimens are specific to factors influencing cranial structure. Collectively, these analyses demonstrate the potential importance of in situ changes in morphology as a response to changing environmental conditions. J. Morphol. 277:96–106, 2016. © 2016 Wiley Periodicals, Inc.     

Incidence of leukaemia in young people in the vicinity of Hinkley Point nuclear power station, 1959-86.

The incidence of leukaemia and non-Hodgkin''s lymphoma in young people (aged under 25) living in a predefined area around the nuclear power station at Hinkley Point, Somerset, was examined for the period 1959-86 by using cancer registry data. During the period since Hinley Point began operations--that is, 1964-86--there were 19 cases in the area compared with 10.4 expected from national rates, giving a standardised registration ratio of 1.82 (95% confidence interval 1.10 to 2.85). The incidence in the rest of Somerset was also high, however (standardised registration ratio 1.18; 95% confidence interval 0.98 to 1.41), and the high rate around Hinkley Point may simply have been reflecting the high local incidence (ratio of the two standardised registration ratio''s 1.54; 95% confidence interval 0.90 to 2.52). Analysis of predetermined five year periods showed that the excess cases in the Hinkley Point area were concentrated in the 10 years 1964-73 after commissioning of the station, at a time when rates in the rest of Somerset were close to the national average. In particular the nine cases occurring in the five years 1969-73 were about four times the number expected from national rates (standardised registration ratio 3.96; 95% confidence interval 1.81 to 7.52). Rates in the Hinkley Point area after 1973 were fairly low, especially as compared with the rest of Somerset. In the five years 1959-63 (that is, before Hinkley Point was commissioned) rates throughout Somerset (including the Hinkley Point area) were higher than the national rate. These findings should be interpreted with caution, and further studies are required to test the plausibility of theories relating to radiation and viruses.     

Structural analysis of mevalonate‐3‐kinase provides insight into the mechanisms of isoprenoid pathway decarboxylases

In animals, cholesterol is made from 5‐carbon building blocks produced by the mevalonate pathway. Drugs that inhibit the mevalonate pathway such as atorvastatin (lipitor) have led to successful treatments for high cholesterol in humans. Another potential target for the inhibition of cholesterol synthesis is mevalonate diphosphate decarboxylase (MDD), which catalyzes the phosphorylation of (R)‐mevalonate diphosphate, followed by decarboxylation to yield isopentenyl pyrophosphate. We recently discovered an MDD homolog, mevalonate‐3‐kinase (M3K) from Thermoplasma acidophilum, which catalyzes the identical phosphorylation of (R)‐mevalonate, but without concomitant decarboxylation. Thus, M3K catalyzes half the reaction of the decarboxylase, allowing us to separate features of the active site that are required for decarboxylation from features required for phosphorylation. Here we determine the crystal structure of M3K in the apo form, and with bound substrates, and compare it to MDD structures. Structural and mutagenic analysis reveals modifications that allow M3K to bind mevalonate rather than mevalonate diphosphate. Comparison to homologous MDD structures show that both enzymes employ analogous Arg or Lys residues to catalyze phosphate transfer. However, an invariant active site Asp/Lys pair of MDD previously thought to play a role in phosphorylation is missing in M3K with no functional replacement. Thus, we suggest that the invariant Asp/Lys pair in MDD may be critical for decarboxylation rather than phosphorylation.