cyanovirin-n cyanovirin-n cyanovirin-n (cv-n) is a protein produced by the cyanobacterium nostoc ellipsosporum that displays virucidal activity against several viruses, including human immunodeficiency virus (hiv). a cyanobacterial protein called cyanovirin-n (cv-n) has strong anti-human immunodeficiency virus (hiv) neutralizing properties. the virucidal activity of cv-n is mediated through specific high-affinity interactions with the viral surface envelope glycoproteins gp120 and gp41, as well as to high-mannose oligosaccharides found on the hiv envelope. in addition, cv-n is active against rhinoviruses, human parainfluenza virus, respiratory syncytial virus, and enteric viruses. the virucidal activity of cv-n against influenza virus is directed towards viral haemagglutinin. the blue-green alga nostoc ellipsosporum naturally contains the protein cyanovirin-n. the national cancer institute (nci) in the united states carried out the initial isolation and characterisation of this protein in 1999. the use of cyanovirin-n as an antiviral drug, particularly against hiv, has since been the subject of investigation. its ability to bind to the hiv-encapsulating glycoprotein gp120 has been demonstrated in several studies, which has led to the development of cyanovirin-n-based therapies and preventatives. structure cyanovirin-n is a lengthy, mostly beta-sheet protein that displays internal two-fold pseudosymmetry. the fundamental atomic root-mean-square of the two sequence repeats (1-50 and 51-101) differs by 1.3 a while sharing 32% of the same sequence. the total fold depends on a number of interactions between the two repetitions, therefore they don't actually belong in separate domains. cv-n has a complex fold composed of a duplication of a tandem repeat of two homologous motifs comprising three-stranded beta-sheet and beta-hairpins.