Heparin or highly sulfated heparan sulfate (HS) has been described in different invertebrates. In ascidians (Chordata-Tunicata), these glycosaminoglycans occur in intracellular granules of oocyte accessory cells and circulating basophil-like cells, resembling mammalian mast cells and basophils, respectively. HS is also a component of the basement membrane of different ascidian organs. We have analyzed an HS isolated from the internal organs of the ascidian Phallusia nigra, using solution 1H/13C NMR spectroscopy, which allowed us to identify and quantify the monosaccharides found in this glycosaminoglycan. A variety of α-glucosamine units with distinct degrees of sulfation and N-acetylation were revealed. The hexuronic acid units occur both as α-iduronic acid and β-glucuronic acid, with variable sulfation at the 2-position. A peculiar structural aspect of the tunicate HS is the high content of 2-sulfated β-glucuronic acid, which accounts for one-third of the total hexuronic acid units. Another distinct aspect of this HS is the occurrence of high content of N-acetylated α-glucosamine units bearing a sulfate group at position 6. The unique ascidian HS is a potent inhibitor of the binding of human colon adenocarcinoma cells to immobilized P-selectin, being 11-fold more potent than mammalian heparin, but almost ineffective as an anticoagulant. Thus, the components of the HS structure required to inhibit coagulation and binding of tumor cells to P-selectin are distinct. Our results also suggest that the regulation of the pathway involved in the biosynthesis of glycosaminoglycans suffered variations during the evolution of chordates.

Flaviviruses, such as dengue, zika, yellow fever, West Nile, and Japanese encephalitis virus, are RNA viruses belonging to the Flaviviridae family (genus Flavivirus). They represent an important global health concern, since most areas of the world are endemic for at least one of these viruses. Although vaccines for five flaviviruses currently exist, there is a need for new vaccines to protect from established, emerging, and reemerging flaviviruses. Yellow fever vaccine shortages experienced in the last decade, combined with the risk of YFV spread to Asia and the restrictions of vaccine administration to certain population segments, show that even when a highly efficacious vaccine is available, new and improved vaccines might be needed. Virus-like particles (VLPs) are multiprotein structures that mimic the virus, but do not contain its genetic material. As such, VLPs have an excellent track record of strong immunogenicity and high safety, dating back to the introduction of the first recombinant hepatitis B vaccine in the 1980s. Flavivirus-like particles (FVLPs) have been extensively studied, especially for DENV, JEV, and ZIKV, and could give rise to next-generation recombinant subunit flavivirus vaccines based on VLPs incorporating molecular features intended to ensure high efficacy and minimize the risk of antibody-dependent enhancement (ADE) upon infection with other flaviviruses.