Unique conformer selection of human growth-regulatory lectin galectin-1 for ganglioside GM1 versus bacterial toxins.
Endogenous lectins induce effects on cell growth by binding to antennae of natural glycoconjugates. These complex carbohydrates often present more than one potential lectin-binding site in a single chain. Using the growth-regulatory interaction of the pentasaccharide of ganglioside GM(1) with homodimeric galectin-1 on neuroblastoma cell surfaces as a model, we present a suitable strategy for addressing this issue. The approach combines NMR spectroscopic and computational methods and does not require isotope-labeled glycans. It involves conformational analysis of the two building blocks of the GM(1) glycan, i.e., the disaccharide Galbeta1-3GalNAc and the trisaccharide Neu5Acalpha2-3Galbeta1-4Glc. Their bound-state conformations were determined by transferred nuclear Overhauser enhancement spectroscopy. Next, measurements on the lectin-pentasaccharide complex revealed differential conformer selection regarding the sialylgalactose linkage in the tri- versus pentasaccharide (Phi and Psi value of -70 degrees and 15 degrees vs 70 degrees and 15 degrees, respectively). To proceed in the structural analysis, the characteristic experimentally detected spatial vicinity of a galactose unit and Trp68 in the galectin's binding site offered a means, exploiting saturation transfer from protein to carbohydrate protons. Indeed, we detected two signals unambiguously assigned to the terminal Gal and the GalNAc residues. Computational docking and interaction energy analyses of the entire set of ligands supported and added to experimental results. The finding that the ganglioside's carbohydrate chain is subject to differential conformer selection at the sialylgalactose linkage by galectin-1 and GM(1)-binding cholera toxin (Phi and Psi values of -172 degrees and -26 degrees, respectively) is relevant for toxin-directed drug design. In principle, our methodology can be applied in studies aimed at blocking galectin functionality in malignancy and beyond glycosciences.
Siebert
Hans-Christian
HC
Institut für Physiologische Chemie, Tierärztliche Fakultät, Ludwig-Maximilians-Universität München, Veterinärstrasse 13, 80539 München, Germany. gabius@lectins.de
André
Sabine
S
Lu
Shan-Yun
SY
Frank
Martin
M
Kaltner
Herbert
H
van Kuik
J Albert
JA
Korchagina
Elena Y
EY
Bovin
Nicolai
N
Tajkhorshid
Emad
E
Kaptein
Robert
R
Vliegenthart
Johannes F G
JF
von der Lieth
Claus-Wilhelm
CW
Jiménez-Barbero
Jesús
J
Kopitz
Jürgen
J
Gabius
Hans-Joachim
HJ
D000116:Acetylgalactosamine / Q000737:chemistry; D001665:Binding Sites; D002240:Carbohydrate Sequence; D045744:Cell Line, Tumor; D002772:Cholera Toxin / Q000737:chemistry* / Q000378:metabolism; D003198:Computer Simulation; D005677:G(M1) Ganglioside / Q000737:chemistry* / Q000378:metabolism; D005690:Galactose / Q000737:chemistry; D037483:Galectin 1 / Q000737:chemistry* / Q000378:metabolism; D006131:Growth Inhibitors / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D009844:Oligosaccharides / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D013816:Thermodynamics; D014364:Tryptophan / Q000737:chemistry
D037483:Galectin 1; D006131:Growth Inhibitors; D009844:Oligosaccharides; D005677:G(M1) Ganglioside; D014364:Tryptophan; D002772:Cholera Toxin; D000116:Acetylgalactosamine; D005690:Galactose