NMR Structural and Biophysical Analysis of the Disease-Linked Inner Mitochondrial Membrane Protein MPV17

MPV17 is an integral inner mitochondrial membrane protein, whose loss-of-function is linked to the hepatocerebral form of the mitochondrial-DNA-depletion syndrome, leading to a tissue-specific reduction of mitochondrial DNA and organ failure in infants. Several disease-causing mutations in MPV17 have been identified and earlier studies with reconstituted protein suggest that MPV17 forms a high conductivity channel in the membrane. However, the molecular and structural basis of the MPV17 functionality remain only poorly understood. In order to make MPV17 accessible to high-resolution structural studies, we here present an efficient protocol for its high-level production in E. coli and refolding into detergent micelles. Using biophysical and NMR methods, we show that refolded MPV17 in detergent micelles adopts a compact structure consisting of six membrane-embedded α-helices. Furthermore, we demonstrate that MPV17 forms oligomers in a lipid bilayer that are further stabilized by disulfide-bridges. In line with these findings, MPV17 could only be inserted into lipid nanodiscs of 8–12 nm in diameter if intrinsic cysteines were either removed by mutagenesis or blocked by chemical modification. Using this nanodisc reconstitution approach, we could show that disease-linked mutations in MPV17 abolish its oligomerization properties in the membrane. These data suggest that, induced by oxidative stress, MPV17 can alter its oligomeric state from a properly folded monomer to a disulfide-stabilized oligomeric pore which might be required for the transport of metabolic DNA precursors into the mitochondrial matrix to compensate for the damage caused by reactive oxygen species.     

Ecological interactions in Aedes species on Reunion Island

Two invasive, container‐breeding mosquito species, Aedes aegypti (Stegomyia aegypti) and Aedes albopictus (Stegomyia albopicta) (Diptera: Culicidae), have different distribution patterns on Reunion Island. Aedes albopictus occurs in all areas and Ae. aegypti colonizes only some restricted areas already occupied by Ae. albopictus. This study investigates the abiotic and biotic ecological mechanisms that determine the distribution of Aedes species on Reunion Island. Life history traits (duration of immature stages, survivorship, fecundity, estimated finite rate of increase) in Ae. aegypti and Ae. albopictus were compared at different temperatures. These fitness measures were characterized in both species in response to competitive interactions among larvae. Aedes aegypti was drastically affected by temperature, performing well only at around 25 °C, at which it achieved its highest survivorship and greatest estimated rate of increase. The narrow distribution of this species in the field on Reunion Island may thus relate to its poor ability to cope with unfavourable temperatures. Aedes aegypti was also more negatively affected by high population densities and to some extent by interactions with Ae. albopictus, particularly in the context of limited food supplies. Aedes albopictus exhibited better population performance across a range of environmental conditions. Its ecological plasticity and its superior competitive ability relative to its congener may further enhance its invasion success on Reunion Island.     

Altered Hippocampal-Prefrontal Neural Dynamics in Mouse Models of Down Syndrome

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Nutrient conservation strategies in native Andean‐Patagonian forests

Abstract. Nutrient conservation in vegetation affects rates of litter decomposition and soil nutrient availability. Although resorption has been traditionally considered one of the most important plant strategies to conserve nutrients in temperate forests, long leaf life‐span and low nutrient requirements have been postulated as better indicators. We aimed at identifying nutrient conservation strategies within characteristic functional groups of NW Patagonian forests on Andisols. We analysed C‐, N‐, P‐, K‐ and lignin‐concentrations in mature and senescent leaves of ten native woody species within the functional groups: broad‐leaved deciduous species, broad‐leaved evergreens and conifers. We also examined mycorrhizal associations in all species. Nutrient concentration in mature leaves and N‐ resorption were higher in broad‐leaved deciduous species than in the other two functional groups. Conifers had low mature leaf nutrient concentrations, low N‐resorption and high lignin/N ratios in senescent leaves. P‐ and K‐resorptions did not differ among functional groups. Broad‐leaved evergreens exhibited a species‐dependent response. Nitrogen in mature leaves was positively correlated with both N resorption and soil N‐fertility. Despite the high P‐retention capacity of Andisols, N appeared to be the more limiting nutrient, with most species being proficient in resorbing N but not P. The presence of endomycorrhizae in all conifers and the broad‐leaved evergreen Maytenus boaria, ectomycorrhizae in all Nothofagus species (four deciduous, one evergreen), and cluster roots in the broad‐leaved evergreen Lomatia hirsuta, would be possibly explaining why P is less limiting than N in these forests.     

Role of electrostatics in the binding of charged metallophthalocyanines to neutral and charged phospholipid membranes

Binding of the cationic tetra(tributylammoniomethyl)-substituted hydroxoaluminum phthalocyanine (AlPcN₄) to bilayer lipid membranes was studied by fluorescence correlation spectroscopy (FCS) and intramembrane field compensation (IFC) methods. With neutral phosphatidylcholine membranes, AlPcN₄ appeared to bind more effectively than the negatively charged tetrasulfonated aluminum phthalocyanine (AlPcS₄), which was attributed to the enhancement of the coordination interaction of aluminum with the phosphate moiety of phosphatidylcholine by the electric field created by positively charged groups of AlPcN₄. The inhibitory effect of fluoride ions on the membrane binding of both AlPcN₄ and AlPcS₄ supported the essential role of aluminum-phosphate coordination in the interaction of these phthalocyanines with phospholipids. The presence of negative or positive charges on the surface of lipid membranes modulated the binding of AlPcN₄ and AlPcS₄ in accord with the character (attraction or repulsion) of the electrostatic interaction, thus showing the significant contribution of the latter to the phthalocyanine adsorption on lipid bilayers. The data on the photodynamic activity of AlPcN₄ and AlPcS₄ as measured by sensitized photoinactivation of gramicidin channels in bilayer lipid membranes correlated well with the binding data obtained by FCS and IFC techniques. The reduced photodynamic activity of AlPcN₄ with neutral membranes violating this correlation was attributed to the concentration quenching of singlet excited states as proved by the data on the AlPcN₄ fluorescence quenching.     

Tests of the accuracy of cladograms in Gilia (Polemoniaceae) and some other angiosperm genera

 This paper deals with the use of cladistic methods and cladograms in phylogeny reconstruction in plant groups containing numerous taxa. How accurate are the cladograms as to details? Accuracy tests at the level of details require an independently known phylogeny, which excludes most plant groups, but such tests can be carried out in domesticated and experimental plant groups which have documented pedigrees. Four such tests are known and are presented here: a new case in Gilia and three previously published cases in Avena, Hordeum, and Helianthus. The four cases include domesticated and experimental plants, use of morphological and molecular evidence, and presence of dichotomous as well as reticulate phylogenies. The cladograms of the four plant groups all differ in significant details from the known pedigrees. These results are discussed in relation to problems of interpretation of cladograms. Received March 21, 2000 Accepted August 16, 2001     

Anatomy and muscle activity of the dorsal fins in bamboo sharks and spiny dogfish during turning maneuvers

Stability and procured instability characterize two opposing types of swimming, steady and maneuvering, respectively. Fins can be used to manipulate flow to adjust stability during swimming maneuvers either actively using muscle control or passively by structural control. The function of the dorsal fins during turning maneuvering in two shark species with different swimming modes is investigated here using musculoskeletal anatomy and muscle function. White‐spotted bamboo sharks are a benthic species that inhabits complex reef habitats and thus have high requirements for maneuverability. Spiny dogfish occupy a variety of coastal and continental shelf habitats and spend relatively more time cruising in open water. These species differ in dorsal fin morphology and fin position along the body. Bamboo sharks have a larger second dorsal fin area and proportionally more muscle insertion into both dorsal fins. The basal and radial pterygiophores are plate‐like structures in spiny dogfish and are nearly indistinguishable from one another. In contrast, bamboo sharks lack basal pterygiophores, while the radial pterygiophores form two rows of elongated rectangular elements that articulate with one another. The dorsal fin muscles are composed of a large muscle mass that extends over the ceratotrichia overlying the radials in spiny dogfish. However, in bamboo sharks, the muscle mass is divided into multiple distinct muscles that insert onto the ceratotrichia. During turning maneuvers, the dorsal fin muscles are active in both species with no differences in onset between fin sides. Spiny dogfish have longer burst durations on the outer fin side, which is consistent with opposing resistance to the medium. In bamboo sharks, bilateral activation of the dorsal in muscles could also be stiffening the fin throughout the turn. Thus, dogfish sharks passively stiffen the dorsal fin structurally and functionally, while bamboo sharks have more flexible dorsal fins, which result from a steady swimming trade off. J. Morphol. 274:1288–1298, 2013. © 2013 Wiley Periodicals, Inc.