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.