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A cyanobacterial protein called cyanovirin-N (CV-N) has strong anti-human immunodeficiency virus (HIV) neutralizing properties. 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.[6] 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.