Background: Viscum album (the European mistletoe) is a semi-parasitic plant, which is
of high medical interest. It is widely found in Europe, Asia, and North America. It contains at least
three distinct lectins (i.e. ML-I, II, and III), varying in molecular mass and specificity. Among
them, ML-I is in focus of medical research for various activities, including anti-cancer activities. To
understand the molecular basis for such medical applications, a few studies have already addressed
the structural and functional analysis of ML-I in complex with ligands. In continuation of these efforts,
we are reporting the crystal structure of ML from Viscum album in complex with the nucleic acid oxidation
product 4-N-furfurylcytosine (FC) refined to 2.85 Å resolution. FC is known to be involved in
different metabolic pathways related to oxidative stress and DNA modification.
Methods: X-ray suitable hexagonal crystals of the ML-I/FC complex were grown within four days
at 294 K using the hanging drop vapor diffusion method. Diffraction data were collected up to a
resolution of 2.85 Å. The ligand affinity was verified by in-silico docking.
Results: The high-resolution structure was refined subsequently to analyze particularly the active
site conformation and a binding epitope of 4-N-furfurylcytosine. A distinct 2Fo-Fc electron density
at the active site was interpreted as a single FC molecule. The specific binding of FC is
achieved also through hydrophobic interactions involving Tyr76A, Tyr115A, Glu165A, and
Leu157A of the ML-I A-chain. The binding energy of FC to the active site of ML-I was calculated
as well to be -6.03 kcal mol-1.
Conclusion: In comparison to other reported ML-I complexes, we observed distinct differences in
the vicinity of the nucleic acid base binding site upon interaction with FC. Therefore, data obtained
will provide new insights in understanding the specificity, inhibition, and cytotoxicity of the ML-I
A-chain, and related RIPs.