Biology subjects

Melo, N.

Publications and source records attributed to Melo, N..

3 recordsLinked to original sources

bioRxiv2020

Stability of the Retinoid X Receptor-alpha Homodimer in the Presence and Absence of Rexinoid and Coactivator Peptide

Differential scanning calorimetry and differential scanning fluorimetry were used to measure the thermal stability of human retinoid X receptor-alpha ligand binding domain (RXR LBD) homodimer in the absence or presence of rexinoid and coactivator peptide, GRIP-1. The apo-RXR LBD homodimer displayed a single thermal unfolding transition with a Tm of 58.7 {degrees}C and an unfolding enthalpy ({Delta}H) of 673 kJ/mol (12.5 J/g), much lower than average value (35 J/g) of small globular proteins. Using a heat capacity change ({Delta}Cp) of 15 kJ/(mol{middle dot}K) determined by measurements at different pH values, the free energy of unfolding ({Delta}G) of the native state was 33 kJ/mol at 37 {degrees}C. Rexinoid binding to the apo-homodimer increased Tm by 5 to 9 {degrees}C, and increased the {Delta}G of the native homodimer by 12 to 20 kJ/mol at 37 {degrees}C, consistent with the nanomolar dissociation constant (Kd) of the rexinoids. The increase in {Delta}G was the result of a more favorable entropic change due to interactions between the rexinoid and hydrophobic residues in the binding pocket, with the larger increases caused by rexinoids containing larger hydrophobic end groups. GRIP-1 binding to holo-homodimers containing rexinoid resulted in additional increases in {Delta}G of 14 kJ/mol, a value same for all three rexinoids. Binding of rexinoid and GRIP-1 resulted in a combined 50% increase in unfolding enthalpy, consistent with reduced structural fluidity and more compact folding observed in other published structural studies. Thermodynamic analysis thus provided a quantitative evaluation of the interactions between RXR and its agonist and coactivator.

biochemistry↗

bioRxiv2020

Large vs small genomes in Passiflora: the influence of the mobilome and the satellitome

Repetitive sequences are ubiquitous and fast-evolving elements responsible for size variation and large-scale organization of plant genomes. Within Passiflora genus, a ten-fold variation in genome size, not attributed to polyploidy, is known. Here, we applied a combined in silico and cytological approach to study the organization and diversification of repetitive elements in three species of these genera representing its known range in genome size variation. Sequences were classified in terms of type and repetitiveness and the most abundant were mapped to chromosomes. We identified Long Terminal Repeat (LTR) retrotransposons as the most abundant elements in the three genomes, showing a considerable variation among species. Satellite DNAs (satDNAs) were less representative, but highly diverse between subgenera. Our results clearly confirm that the largest genome species (Passiflora quadrangularis) presents a higher accumulation of repetitive DNA sequences, specially Angela and Tekay elements, making up most of its genome. Passiflora cincinnata, with intermediate genome and from the same subgenus, showed similarity with P. quadrangularis regarding the families of repetitive DNA sequences, but in different proportions. On the other hand, Passiflora organensis, the smallest genome, from a different subgenus, presented greater diversity and the highest proportion of satDNA. Altogether, our data indicate that while large genome evolve by an accumulation of retrotransponsons, small genomes most evolved by diversification of different repeat types, particularly satDNAs. MAIN CONCLUSIONSWhile two lineages of retrotransposons were more abundant in larger Passiflora genomes, the satellitome was more diverse and abundant in the smallest genome.

evolutionary biology↗

bioRxiv2019

Geosmin attracts Aedes aegypti mosquitoes to oviposition sites

Geosmin is one of the most recognizable and common microbial smells on the planet. Some insects, like mosquitoes, require microbial-rich environments for their progeny, whereas for other insects such microbes may prove dangerous. In the vinegar fly Drosophila melanogaster, geosmin is decoded in a remarkably precise fashion and induces aversion, presumably signaling the presence of harmful microbes. We have here investigated the effect of geosmin on the behavior of the yellow fever mosquito Aedes aegypti. In contrast to flies, geosmin is not aversive in mosquitoes but stimulates egg-laying site selection. Female mosquitoes could associate geosmin with microbes, including cyanobacteria consumed by larvae, who also find geosmin - as well as geosmin producing cyanobacteria - attractive. Using in vivo multiphoton imaging from mosquitoes with pan-neural expression of the calcium reporter GCaMP6s, we show that Ae. aegypti code geosmin in a similar fashion to flies, i.e. with extreme sensitivity and with a high degree of selectivity. We further demonstrate that geosmin can be used as bait under field conditions, and finally we show that geosmin, which is both expensive and difficult to obtain, can be substituted by beetroot peel extract, providing a cheap and viable mean of mosquito control and surveillance in developing countries.

neuroscience↗