Detailed insights from microarray and crystallographic studies into carbohydrate recognition by microneme protein 1 (MIC1) of Toxoplasma gondii.
The intracellular protozoan Toxoplasma gondii is among the most widespread parasites. The broad host cell range of the parasite can be explained by carbohydrate microarray screening analyses that have demonstrated the ability of the T. gondii adhesive protein, TgMIC1, to bind to a wide spectrum of sialyl oligosaccharide ligands. Here, we investigate by further microarray analyses in a dose-response format the differential binding of TgMIC1 to 2-3- and 2-6-linked sialyl carbohydrates. Interestingly, two novel synthetic fluorinated analogs of 3'SiaLacNAc(1-4) and 3'SiaLacNAc(1-3) were identified as highly potent ligands. To understand the structural basis of the carbohydrate binding specificity of TgMIC1, we have determined the crystal structures of TgMIC1 micronemal adhesive repeat (MAR)-region (TgMIC1-MARR) in complex with five sialyl-N-acetyllactosamine analogs. These crystal structures have revealed a specific, water-mediated hydrogen bond network that accounts for the preferential binding of TgMIC1-MARR to arrayed 2-3-linked sialyl oligosaccharides and the high potency of the fluorinated analogs. Furthermore, we provide strong evidence for the first observation of a C--F...H--O hydrogen bond within a lectin-carbohydrate complex. Finally, detailed comparison with other oligosaccharide-protein complexes in the Protein Data Bank (PDB) reveals a new family of sialic-acid binding sites from lectins in parasites, bacteria, and viruses.
Garnett
James A
JA
Division of Molecular Biosciences, Centre for Structural Biology, Imperial College London, South Kensington, London SW72AZ, United Kingdom.
Liu
Yan
Y
Leon
Ester
E
Allman
Sarah A
SA
Friedrich
Nikolas
N
Saouros
Savvas
S
Curry
Stephen
S
Soldati-Favre
Dominique
D
Davis
Benjamin G
BG
Feizi
Ten
T
Matthews
Stephen
S
D000606:Amino Sugars / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002240:Carbohydrate Sequence; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008969:Molecular Sequence Data; D040081:Protein Array Analysis; D011485:Protein Binding; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism*; D014122:Toxoplasma / Q000378:metabolism*
D000606:Amino Sugars; D015815:Cell Adhesion Molecules; C105877:MIC1 protein, Toxoplasma gondii; D015800:Protozoan Proteins; C032269:sialyl-N-acetyllactosamine