Structure and Glycan Binding of a New Cyanovirin-N Homolog

The HIV-1 envelope glycoprotein gp120 is heavily glycosylated and bears numerous high mannose sugars. These sugars can serve as targets for HIV-inactivating compounds, such as antibodies and lectins, which bind to the glycans and interfere with viral entry into the target cell. We determined the 1.6 Å x-ray structure of Cyt-CVNH, a recently identified lectin from the cyanobacterium Cyanothece(7424), and elucidated its glycan specificity by NMR. The Cyt-CVNH structure and glycan recognition profile are similar to those of other CVNH proteins, with each domain specifically binding to Manα(1-2)Manα units on the D1 and D3 arms of high mannose glycans. However, in contrast to CV-N, no cross-linking and precipitation of the cross-linked species in solution was observed upon Man-9 binding, allowing, for the first time, investigation of the interaction of Man-9 with a member of the CVNH family by NMR. HIV assays showed that Cyt-CVNH is able to inhibit HIV-1 with ∼4-fold higher potency than CV-N(P51G), a stabilized version of wild type CV-N. Therefore, Cyt-CVNH may qualify as a valuable lectin for potential microbicidal use.