Table 1.

Comparison of Parasite Ligands^a

Properties	TgMIC1	PfEBA175b
Target cell	Nucleated Cellc	Erythrocyte
Target receptor	Branched carbohydrates with two or more terminal sialic acidsd	N-acetylneuraminic acid (Neu5Ac)(α2, 3)-Gal on glycophorin A (GpA)
No. of ligand subunits	Monomer	Dimer
Adhesive domain nomenclature	MAR	DBL
Secondary structure composition	β-sheet enriched	α-helices enriched
No. of disulfide bonds formed within parasite protein	6–8	13
Receptor-ligand biochemistry	Novel hydrogen bonding	Salt-bridge bonding
Contact residues involved in glycan bindinge, f	YY219g, R217g, T126g, K216g, H218g, T220g.	N417h, R422h, N429 h, K439h, D422h, K28 h; N33i, N550i, N551i, Y552ii, K553i, M554i; T340j, K341j, D342j V343j, Y415j, Q542j, Y546j, K28j, N29j, R31j, S32j
No. of glycan binding sites	2	6
Location of glycan binding sites	Occurs centrally with each MAR domain	Occurs at dimer interface
Spacing between glycan binding sites	32.3 Åk	40.4 to 44.8 A depending on the pair

^aParasite protein is referred to as the ligand in Blumschein et al. ¹⁰

^bEBA175 structural components were obtained from Tolia et al. ¹⁶

^cTissue cyst tropisms are observed in the central nervous system, eye, and muscle tissue ²⁰, ²⁴, ²⁵.

^dOptimal binding for the MAR domains occurs when five to eight carbohydrates units separate the sialic acid termini.

^eBold residues: Mutagenesis of these residues greatly decreased glycan binding.

^fResidues between K216 and E221 form a shallow binding pocket in the MAR2 domain and most of these residues make specific, direct contacts with the sialy moiety¹⁰.

^gKey binding residues for TgMIC1. Note: double mutant T126/T220 completely abrogates glycan binding.

^hContact sites for binding of glycans 1 and 2.

ⁱContact sites for binding of glycans 3 and 4

^jContact sites for binding of glycans 5 and 6

^kÅ=Angstrom