[Show abstract][Hide abstract]ABSTRACT: Angiotensin-converting enzyme 2 (ACE2), a newly identified member in the renin-angiotensin system (RAS), acts as a negative regulator of ACE. It is mainly expressed in cardiac blood vessels and the tubular epithelia of kidneys and abnormal expression has been implicated in diabetes, hypertension and heart failure. The mechanism and physiological function of this zinc metallopeptidase in mammals are not yet fully understood. Non-mammalian vertebrate models offer attractive and simple alternatives that could facilitate the exploration of ACE2 function. In this paper we report the in silico analysis of Ace2 genes from the Gallus (chicken), Xenopus (frog), Fugu and Tetraodon (pufferfish) genome assembly databases, and from the Danio (zebrafish) cDNA library. Exon ambiguities of Danio and Xenopus Ace2s were resolved by RT-PCR and 3'RACE. Analyses of the exon-intron structures, alignment, phylogeny and hydrophilicity plots, together with the conserved synteny among these vertebrates, support the orthologous relationship between mammalian and non-mammalian ACE2s. The putative promoters of Ace2 from human, Tetraodon and Xenopus tropicalis drove the expression of enhanced green fluorescent protein (EGFP) specifically in the heart tissue of transgenic Xenopus thus making it a suitable model for future functional genomic studies. Additionally, the search for conserved cis-elements resulted in the discovery of WGATAR motifs in all the putative Ace2 promoters from 7 different animals, suggesting a possible role of GATA family transcriptional factors in regulating the expression of Ace2.
[Show abstract][Hide abstract]ABSTRACT: The spike (S) protein of the severe acute respiratory syndrome coronavirus (SARS-CoV) interacts with cellular receptors to mediate membrane fusion, allowing viral entry into host cells; hence it is recognized as the primary target of neutralizing antibodies, and therefore knowledge of antigenic determinants that can elicit neutralizing antibodies could be beneficial for the development of a protective vaccine. Here, we expressed five different fragments of S, covering the entire ectodomain (amino acids 48 to 1192), as glutathione S-transferase fusion proteins in Escherichia coli and used the purified proteins to raise antibodies in rabbits. By Western blot analysis and immunoprecipitation experiments, we showed that all the antibodies are specific and highly sensitive to both the native and denatured forms of the full-length S protein expressed in virus-infected cells and transfected cells, respectively. Indirect immunofluorescence performed on fixed but unpermeabilized cells showed that these antibodies can recognize the mature form of S on the cell surface. All the antibodies were also able to detect the maturation of the 200-kDa form of S to the 210-kDa form by pulse-chase experiments. When the antibodies were tested for their ability to inhibit SARS-CoV propagation in Vero E6 culture, it was found that the anti-SDelta10 antibody, which was targeted to amino acid residues 1029 to 1192 of S, which include heptad repeat 2, has strong neutralizing activities, suggesting that this region of S carries neutralizing epitopes and is very important for virus entry into cells.
Full-text · Article · Apr 2005 · Journal of Virology