Near-atomic structure of an atadenovirus reveals a conserved capsid-binding motif and intergenera variations in cementing proteins

Of five known adenovirus genera, high-resolution structures are available only for mammalian-infecting mastadenoviruses. We present the first high-resolution structure of an adenovirus with nonmammalian host: lizard atadenovirus LAdV-2. We find a large conformational difference in the internal vertex protein IIIa between mast- and atadenoviruses, induced by the presence of an extended polypeptide. This polypeptide, and α-helical clusters beneath the facet, likely correspond to genus-specific proteins LH2 and p32k. Another genus-specific protein, LH3, with a fold typical of bacteriophage tailspikes, contacts the capsid surface via a triskelion structure identical to that used by mastadenovirus protein IX, revealing a conserved capsid-binding motif and an ancient gene duplication event. Our data also suggest that mastadenovirus E1B-55 K was exapted from the atadenovirus-like LH3 protein. This work provides new information on the evolution of adenoviruses, emphasizing the importance of minor coat proteins for determining specific physicochemical properties of virions and most likely their tropism.

An algal enzyme required for biosynthesis of the most abundant marine carotenoids

Fucoxanthin and its derivatives are the main light-harvesting pigments in the photosynthetic apparatus of many chromalveolate algae and represent the most abundant carotenoids in the world’s oceans, thus being major facilitators of marine primary production. A central step in fucoxanthin biosynthesis that has been elusive so far is the conversion of violaxanthin to neoxanthin. Here, we show that in chromalveolates, this reaction is catalyzed by violaxanthin de-epoxidase–like (VDL) proteins and that VDL is also involved in the formation of other light-harvesting carotenoids such as peridinin or vaucheriaxanthin. VDL is closely related to the photoprotective enzyme violaxanthin de-epoxidase that operates in plants and most algae, revealing that in major phyla of marine algae, an ancient gene duplication triggered the evolution of carotenoid functions beyond photoprotection toward light harvesting.

Non-digestible proteins and protease inhibitors: implications for defense of the colored eggs of the freshwater apple snailPomacea canaliculata

Apple snails (Pomacea Perry, 1810) are successful invaders that cause ecological perturbations, economic losses, and medical issues. A peculiar trait of this snail is a high biological potential, related to the absence of predators of their eggs. Eggs show protease inhibitor (PI) activity, originally ascribed to PcOvo perivitellin in the apple snail Pomacea canaliculata (Lamarck, 1822) but absent in PmPV1, the orthologoue of PcOvo, in eggs of the apple snail Pomacea maculata Perry, 1810. As egg fluid diminishes rat growth rate, an antidigestive effect, similar to plant defenses against herbivory, was hypothesized. However, PI activity has not been characterized in apple snail eggs. Here we identify and partially characterize P. canaliculata egg PI and improve our knowledge of the quaternary structure and evolution of PcOvo. Through N-terminal, transcriptomic or proteomic sequencing, and biochemical validation, we identified a Kunitz-type and a Kazal-type inhibitor that, though at low concentration in the egg, exhibit strong PI activity against trypsin, chymotrypsin, elastase, and subtilisin. Additionally, we report three new subunits for the non-digestible storage protein PcOvo. They are likely products of ancient gene duplication, as their sequences exhibit moderate similarity (30%). To our knowledge, this is the first report of Kazal-type inhibition among invertebrate eggs. Inhibiting varied proteases, PI seems an efficient adaptive trait that limits predator’s capacity to digest egg nutrients.