Isolation and characterization of Myrianthus holstii lectin, a potent HIV-1 inhibitory protein from the plant Myrianthus holstii

Aqueous extracts from the African plant Myrianthus holstii potently inhibited the infection of the T-lymphoblastoid cell line, CEM-SS; by human immunodeficiency virus-1(RF) (HIV-1(RF)). The active constituent, M. holstii lectin (MHL), was purified by LH-20 column chromatography and reversed phase HPLC. MHL, a 9284-Da cysteine-rich protein, was characterized by amino acid analysis, N-terminal sequencing, ESIMS, and matrix-assisted laser-desorption ionization-time-of-flight mass spectrometry. Pure MHL had anti-MN activity, with an EC50 value of 150 nM. Delaying the addition of MHL for up to 8 h after initial exposure of CEM-SS cells to virus did not result in loss of the antiviral activity; however, if addition of the compound was delayed for 16 h or more, there was a marked decrease in the antiviral activity. MHL bound to a virus-free, soluble form of the viral envelope protein gp120 but did not inhibit the subsequent binding to a cell-free, soluble form of the cellular receptor CD4.