Mannose-binding lectin. In solution exists as a metastable domain-swapped homodimer which very slowly converts into a more stable monomeric form at room temperature. Under physiological conditions it is unlikely that the dimeric species exists and indeed the monomer is more active against HIV. Interacts with HIV-1 gp120. Cleavage, or reduction and alkylation of the disulfide bonds results in the loss of anti-HIV activity. Overexpression of this protein to provide quantities adequate for medical use as a topical microbiocide has been attempted in a number of systems including E.coli (PubMed:9210678, PubMed:19547966), Lactobacillus jensenii (PubMed:17005802), the yeast Pichia pastoris (PubMed:12356469) and Nicotiana tabacum (PubMed:16354721); see PubMed:20162270 for a review. Its activity in situ is unknown, however it acts as a viral entry inhibitor, inhibiting HIV-1, HIV-2 and simian immunodeficiency virus (and some other viruses such as feline immunodeficiency virus, measles virus and human herpesvirus) infection and replication. It prevents essential interactions between the envelope glycoprotein and target cell receptors by binding to carbohydrates on viral protein gp120 and possibly by other mechanisms as well. Addition to cells must occur before or shortly after virus addition. It also inhibits cell-to-cell fusion, and virus-to-cell and cell-to-cell transmission of a viral infection. Is remarkably stabile; the protein can withstand multiple freeze-thaw cycles, dissolution in organic solvents, treatment with salt, detergent, H(2)O(2) and boiling without significant loss of anti-HIV activity. Belongs to the cyanovirin-N family.