About the Lectin

HHA reacts not only with terminal but also with
internal alpha-D-mannosyl residues. Sugar hapten inhibition
studies showed this lectin to possess the greatest specific activity
for alpha-D-mannosyl units whereas D-Glc and D-GlcNAc did
not inhibit the lectin precipitation system. Oligosaccharides
containing either 1,3- or 1,6-linked mannosyl units were good
inhibitors of the HHA-mannan precipitation system (6- to 20-
fold more active than D-Man).¹

Mannose-binding lectins, isolated from daffodil (NPA),
amaryllis (HHA), and snowdrop (GNA) bulbs, are capable of
precipitating with a linear mannopentaose (Man alpha 1-3Man
alpha 1-3Man alpha 1-3Man alpha 1-2Man). NPA and HHA
reacted strongly with the mannopentaose whereas GNA gave
a precipitate only at concentrations greater than 500 microM. A
phosphate group at C-6 of the nonreducing terminal mannosyl
group prevented precipitation in all three cases. The reduced
(NaBH4) mannopentaose, Man4Man-ol, did not precipitate
with GNA or NPA, but was active with HHA. This activity was
lost when Man4Man-ol was converted (NaIO4 then NaBH4;
mild acid hydrolysis of the reduced product) into trisaccharide
derivatives.²

The plant lectins derived from Galanthus nivalis
(Snowdrop) (GNA) and Hippeastrum hybrid (Amaryllis) (HHA)
selectively inhibited a wide variety of human immunodeficiency
virus type 1 (HIV-1) and HIV-2 strains and clinical (CXCR4- and
CCR5-using) isolates in different cell types. They also efficiently
inhibited infection of T lymphocytes by a variety of mutant
virus strains. GNA and HHA markedly prevented syncytium
formation between persistently infected HUT-78/HIV cells and
uninfected T lymphocytes. The plant lectins did not measurably
affect the antiviral activity of other clinically approved anti-HIV
drugs used in the clinic when combined with these drugs. Short
exposure of the lectins to cell-free virus particles or persistently
HIV-infected HUT-78 cells markedly decreased HIV infectivity
and increased the protective (microbicidal) activity of the plant
lectins. Flow cytometric analysis and monoclonal antibody
binding studies and a PCR-based assay revealed that GNA and
HHA do not interfere with CD4, CXCR4, CCR5, and DC-SIGN
and do not specifically bind with the membrane of uninfected
cells. Instead, GNA and HHA likely interrupt the virus entry
process by interfering with the virus envelope glycoprotein.

HHA and GNA are odorless, colorless, and tasteless,
and they are not cytotoxic, antimetabolically active, or mitogenic
to human primary T lymphocytes at concentrations that
exceed their antivirally active concentrations by 2 to 3 orders
of magnitude. GNA and HHA did not agglutinate human
erythrocytes and were not toxic to mice when administered
intravenously.³

REFERENCES

1. Kaku H. et al. Arch Biochem Biophys. 1990 Jun;279(2):298-304.
2. Kaku H, et al. Carbohydr Res. 1992 May 22;229(2):337-46.
3. Balzarini J, et al.Antimicrob Agents Chemother. 2004 Oct;48(10):
   3858-70.