Structural highlights
Function
ML1_VISAL The A chain is responsible for inhibiting protein synthesis through the catalytic inactivation of 60S ribosomal subunits by removing adenine from position 4,324 of 28S rRNA. The B chain binds to cell receptors and probably facilitates the entry into the cell of the A chain; B chains are also responsible for cell agglutination (lectin activity). Inhibits growth of the human tumor cell line Molt4.[1] [2] [3]
Evolutionary Conservation
Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.
Publication Abstract from PubMed
The X-ray structure of mistletoe lectin I (MLI), a type-II ribosome-inactivating protein (RIP), cocrystallized with galactose is described. The model was refined at 3.0 A resolution to an R-factor of 19.9% using 21 899 reflections, with Rfree 24.0%. MLI forms a homodimer (A-B)2 in the crystal, as it does in solution at high concentration. The dimer is formed through contacts between the N-terminal domains of two B-chains involving weak polar and non-polar interactions. Consequently, the overall arrangement of sugar-binding sites in MLI differs from those in monomeric type-II RIPs: two N-terminal sugar-binding sites are 15 A apart on one side of the dimer, and two C-terminal sugar-binding sites are 87 A apart on the other side. Galactose binding is achieved by common hydrogen bonds for the two binding sites via hydroxy groups 3-OH and 4-OH and hydrophobic contact by an aromatic ring. In addition, at the N-terminal site 2-OH forms hydrogen bonds with Asp27 and Lys41, and at the C-terminal site 3-OH and 6-OH undergo water-mediated interactions and C5 has a hydrophobic contact. MLI is a galactose-specific lectin and shows little affinity for N-acetylgalactosamine. The reason for this is discussed. Structural differences among the RIPs investigated in this study (their quaternary structures, location of sugar-binding sites, and fine sugar specificities of their B-chains, which could have diverged through evolution from a two-domain protein) may affect the binding sites, and consequently the cellular transport processes and biological responses of these toxins.
Crystal structure at 3 A of mistletoe lectin I, a dimeric type-II ribosome-inactivating protein, complexed with galactose.,Niwa H, Tonevitsky AG, Agapov II, Saward S, Pfuller U, Palmer RA Eur J Biochem. 2003 Jul;270(13):2739-49. PMID:12823544[4]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Kourmanova AG, Soudarkina OJ, Olsnes S, Kozlov JV. Cloning and characterization of the genes encoding toxic lectins in mistletoe (Viscum album L). Eur J Biochem. 2004 Jun;271(12):2350-60. PMID:15182350 doi:http://dx.doi.org/10.1111/j.1432-1033.2004.04153.x
- ↑ Mishra V, Sharma RS, Yadav S, Babu CR, Singh TP. Purification and characterization of four isoforms of Himalayan mistletoe ribosome-inactivating protein from Viscum album having unique sugar affinity. Arch Biochem Biophys. 2004 Mar 15;423(2):288-301. PMID:15001393 doi:http://dx.doi.org/10.1016/j.abb.2003.12.033
- ↑ Dietrich JB, Ribereau-Gayon G, Jung ML, Franz H, Beck JP, Anton R. Identity of the N-terminal sequences of the three A chains of mistletoe (Viscum album L.) lectins: homology with ricin-like plant toxins and single-chain ribosome-inhibiting proteins. Anticancer Drugs. 1992 Oct;3(5):507-11. PMID:1450445
- ↑ Niwa H, Tonevitsky AG, Agapov II, Saward S, Pfuller U, Palmer RA. Crystal structure at 3 A of mistletoe lectin I, a dimeric type-II ribosome-inactivating protein, complexed with galactose. Eur J Biochem. 2003 Jul;270(13):2739-49. PMID:12823544
