Symmetry, orientation and rotational mobility in the a3 heme of cytochrome c oxidase in the inner membrane of mitochondria

The photoinduced linear dichroism of absorption changes resulting from photolysis of the complex between heme a₃ of the cytochrome oxidase and CO is studied. The experiments started from isotropic solutions or suspensions of the enzyme both in its isolated form and in mitochondria. The anisotropy responsible for the linear dichroism was induced by excitation with a flash of linearly polarized light. The dichroic ratios observed with various systems; polymerized enzyme in solution, enzyme in mitochondria and in submitochondrial particles (at 20 °C as well as at liquid N₂-temperature) all approached a value of 4/3 which characterizes a chromophore which is circularly degenerate. Therefrom we conclude that the interaction of heme a₃ with its microenvironment within the protein does not break its four-fold symmetry.

The experiments with mitochondria and submitochondrial particles suspended in aqueous buffer revealed similarly high dichroic ratios without any dichroic relaxation other than a rather slow one which could be attributed to the rotation of the whole organelle in the suspending medium. Therefrom we conclude that the cytochrome oxidase either is totally immobilized in the membrane, or that it carries out only limited rotational diffusion around a single axis coinciding with the symmetry axis of heme a₃. In the light of independent evidence for a transmembrane arrangement of the oxidase and for the general fluidity of the inner mitochondrial membrane we consider anisotropic mobility of the cytochrome oxidase around an axis normal to the plane of the membrane as the most likely interpretation. Then our experimental results imply that the plane of heme a₃ is coplanar to the membrane.     

Assessment of variation of nest survival for grassland birds due to method of nest discovery

Capsule Interpretation of nest survival estimates may be improved by incorporating the search method used to locate nests as a covariate.

Aims To compare annual survival estimates for Dickcissel Spiza americana nests and determine if incorporating search method (structured, opportunistic, or behavioural searches) improved model fit.

Methods Dickcissel nests were located using structured, opportunistic, or behavioural searches over three years (2011–2013) in Mississippi, USA. Models were used to estimate daily survival rates (DSRs) and to analyse factors influencing nest survival.

Results DSRs for Dickcissels were best explained by quadratic date, nest age, age found, and year, but incorporating search method improved model fit. Daily survival was 1.51 times greater for nests located using opportunistic search methods relative to structured searches, but was not significantly different between structured and behavioural searches.

Conclusions Survival estimates varied by search method, specifically between structured searches and opportunistically located nests. This might have arisen because heterogeneity in nest placement or parental behaviour may influence the sample of nests located with a given search method. Researchers may be able to account for this potential source of bias by including search method as a model covariate when using standard survey designs or modelling approaches.     

Effects of vulture exclusion on carrion consumption by facultative scavengers

Vultures provide an essential ecosystem service through removal of carrion, but globally, many populations are collapsing and several species are threatened with extinction. Widespread declines in vulture populations could increase the availability of carrion to other organisms, but the ways facultative scavengers might respond to this increase have not been thoroughly explored. We aimed to determine whether facultative scavengers increase carrion consumption in the absence of vulture competition and whether they are capable of functionally replacing vultures in the removal of carrion biomass from the landscape. We experimentally excluded 65 rabbit carcasses from vultures during daylight hours and placed an additional 65 carcasses that were accessible to vultures in forested habitat in South Carolina, USA during summer (June–August). We used motion‐activated cameras to compare carrion use by facultative scavenging species between the experimental and control carcasses. Scavenging by facultative scavengers did not increase in the absence of competition with vultures. We found no difference in scavenger presence between control carcasses and those from which vultures were excluded. Eighty percent of carcasses from which vultures were excluded were not scavenged by vertebrates, compared to 5% of carcasses that were accessible to vultures. At the end of the 7‐day trials, there was a 10.1‐fold increase in the number of experimental carcasses that were not fully scavenged compared to controls. Facultative scavengers did not functionally replace vultures during summer in our study. This finding may have been influenced by the time of the year in which the study took place, the duration of the trials, and the spacing of carcass sites. Our results suggest that under the warm and humid conditions of our study, facultative scavengers would not compensate for loss of vultures. Carcasses would persist longer in the environment and consumption of carrion would likely shift from vertebrates to decomposers. Such changes could have substantial implications for disease transmission, nutrient cycling, and ecosystem functioning.     

RAB-10-Dependent Membrane Transport Is Required for Dendrite Arborization

Formation of elaborately branched dendrites is necessary for the proper input and connectivity of many sensory neurons. Previous studies have revealed that dendritic growth relies heavily on ER-to-Golgi transport, Golgi outposts and endocytic recycling. How new membrane and associated cargo is delivered from the secretory and endosomal compartments to sites of active dendritic growth, however, remains unknown. Using a candidate-based genetic screen in C. elegans, we have identified the small GTPase RAB-10 as a key regulator of membrane trafficking during dendrite morphogenesis. Loss of rab-10 severely reduced proximal dendritic arborization in the multi-dendritic PVD neuron. RAB-10 acts cell-autonomously in the PVD neuron and localizes to the Golgi and early endosomes. Loss of function mutations of the exocyst complex components exoc-8 and sec-8, which regulate tethering, docking and fusion of transport vesicles at the plasma membrane, also caused proximal dendritic arborization defects and led to the accumulation of intracellular RAB-10 vesicles. In rab-10 and exoc-8 mutants, the trans-membrane proteins DMA-1 and HPO-30, which promote PVD dendrite stabilization and branching, no longer localized strongly to the proximal dendritic membranes and instead were sequestered within intracellular vesicles. Together these results suggest a crucial role for the Rab10 GTPase and the exocyst complex in controlling membrane transport from the secretory and/or endosomal compartments that is required for dendritic growth.     

Identification of MarvelD3 as a tight junction-associated transmembrane protein of the occludin family

Background

Protein translocation across the membrane of the Endoplasmic Reticulum (ER) is the first step in the biogenesis of secretory and membrane proteins. Proteins enter the ER by the Sec61 translocon, a proteinaceous channel composed of three subunits, α, β and γ. While it is known that Sec61α forms the actual channel, the function of the other two subunits remains to be characterized.

Results

In the present study we have investigated the function of Sec61β in Drosophila melanogaster. We describe its role in the plasma membrane traffic of Gurken, the ligand for the Epidermal Growth Factor (EGF) receptor in the oocyte. Germline clones of the mutant allele of Sec61β show normal translocation of Gurken into the ER and transport to the Golgi complex, but further traffic to the plasma membrane is impeded. The defect in plasma membrane traffic due to absence of Sec61β is specific for Gurken and is not due to a general trafficking defect.

Conclusion

Based on our study we conclude that Sec61β, which is part of the ER protein translocation channel affects a post-ER step during Gurken trafficking to the plasma membrane. We propose an additional role of Sec61β beyond protein translocation into the ER.     

Hematozoa and a new haemoproteid species from Cathartidae (New World vulture) in South Carolina

A survey of turkey vultures (Cathartes aura) in South Carolina revealed the presence of a novel haemoproteid. Haemoproteus catharti n. sp. is described from the slides developed from the blood of this vulture. The new species is a thick, halteridial form with complete margins, and is considered distinct from the other recognized haemoproteids from the diurnal raptors in shape, pigment number, parasite outline, and host-family specificity. While reviewing blood films, a series of unusual immature schizonts of Plasmodium sp. were also observed, and these are illustrated, along with another distinct haemoproteid from old slides of poor quality produced from turkey vulture blood.     

Identification of vertebrate scavengers of small mammal carcasses in a forested landscape

We identified vertebrate scavengers of small mammal carcasses at the 780-km² Savannah River Site during the winter of 2000–2001. Rodent carcasses, differing in size and visual conspicuousness, were placed in upland pine forests and bottomland hardwood forests during six 2-week periods. Sixty-two of the 96 carcasses (65%) were removed by vertebrates. With the aid of remote photography, we identified 11 species of scavengers removing carcasses. RaccoonsProcyon lotor, gray foxesUrocyon cinereoargenteus, and feral pigsSus scrofa scavenged most frequently. The mean elapsed time for carcass removal was 5.6 days. The number of carcasses removed by vertebrates did not differ significantly with respect to carcass size, visual conspicuousness, or habitat type; however, air temperature was strongly correlated (positively) with carcass removal. Our study demonstrates that many mammal species are capable of utilizing small carrion items as a food resource, and suggests that scavenging may account for a higher proportion of the diet of some facultative scavengers than is now widely assumed.     

The effect of glutaraldehyde fixation on the primary photochemical processes in bacterial photosynthesis

In Chromatium D the half-time for laser-induced (20–30-nsec flash) cytochrome C553 oxidation in redox poised chromatophores (1 μsec) and cytochrome C555 oxidation in whole cells (2.5μsec) is not affected by glutaraldehyde fixation. The reduction half-times for both cytochromes, however, increase as different functions of the glutaraldehyde concentration during the whole cell fixation process. At a cell-fixing concentration of 0.8%, cytochrome C555 but not C553 is observed after a laser flash. Steady light-induced spectra using similar preparations suggest the possibility of four components observable in the 500–620-nm range. These are cytochrome C555, P600, a species peaking at 560 nm and a component displaying a light-induced blue shift in the 500–540-nm region which may be a carotenoid response. The wavelength expected for the α-peak (reduced-minus-oxidized) of cytochrome cc′ is 560 nm, but the lack of a corresponding Soret peak makes identification uncertain and raises the possibility that we are observing a totally new component. Comparison of the amount of cytochrome oxidized by steady illumination and by a laser flash shows that on the average there are three cytochrome C555 molecules per reaction center in both whole cells and chromatophores. If the glutaraldehyde acts directly on the reaction center cytochromes then it is clear that cytochrome reduction requires large amplitude motion, but that oxidation does not. However, glutaraldehyde fixation may simply block the path of reducing electrons before they reach reaction center bound cytochromes.