tailieunhanh - Báo cáo khoa học: ˚ Crystal structure at 3 A of mistletoe lectin I, a dimeric type-II ribosome-inactivating protein, complexed with galactose

The X-ray structure of mistletoe lectin I (MLI), a type-II ribosome-inactivatingprotein (RIP), cocrystallized with galactose is described. The model was refined at A ˚ resolution to an R-factor of using21 899 reflections, with Rfree . MLI forms a homodimer (A–B)2in 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 involvingweak polar and non-polar interactions. | Eur. J. Biochem. 270 2739-2749 2003 FEBS 2003 doi Crystal structure at 3 A of mistletoe lectin I a dimeric type-II ribosome-inactivating protein complexed with galactose Hideaki Niwa1 Alexander G. Tonevitskv2. Iaor I. Aaanov3 Steve Saward1 Uwe Pfiiller4 and Rex A Palmer1 I I bi 1School of Crystallography Birkbeck College University of London Malet Street London WC1E 7HX UK 2Institute of Transplantology and Artificial Organs Moscow Russia 3Institute of Genetics and Selection of Microorganisms Moscow Russia 4Institut fur Phytochemie Universitat Witten Herdecke Witten Germany The X-ray structure of mistletoe lectin I MLI a type-II ribosome-inactivating protein IRIP . oocrystallized with galactose is described. The model was refined at A resolution to an R-factor of using 21 899 reflection with Rfree . 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 111x1 nonpolar interactions. Consequently the overall arrangement of sugar-binding sites in MLI differs from those in monomeric type-II RIPs two N-teaminal sugar-binding sites are 15 A apart on one side of the dimer and two C-terminal sugar-binding sites tire 77 k. apart on the other side. Galactose bindingis achieved by common hydrogen bonds for the two binding sítes via hydi oxy t roups 3-OH nixl 4-OH ndd hydrophobic contact by an aromatic ring. In addition at the N-terminal site 2--O forms hydrogen bonds with Asp27 and Lys41 and at the C-terminal site 3-OO and 6-OO 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 RPPs ínvetti-gated in this study their quaternary structures location of sugar-binding sites and fine sugar specificities of their B-chains which .