4CHM: Structure Of Inner Membrane Complex (imc) Sub-compartment Protein 1 (isp1) From Toxoplasma Gondii

Citation:
Abstract
Toxoplasma gondii, an apicomplexan parasite prevalent in developed nations, infects up to one-third of the human population. The success of this parasite depends on several unique structures including an inner membrane complex (IMC) that lines the interior of the plasma membrane and contains proteins important for gliding motility and replication. Of these proteins, the IMC sub-compartment proteins (ISPs) have recently been shown to play a role in asexual T. gondii daughter cell formation, yet the mechanism is unknown. Complicating mechanistic characterization of the ISPs is a lack of sequence identity with proteins of known structure or function. In support of elucidating the function of ISPs, we first determined the crystal structures of representative members TgISP1 and TgISP3 to a resolution of 2.10 and 2.32 A, respectively. Structural analysis revealed that both ISPs adopt a pleckstrin homology fold often associated with phospholipid binding or protein-protein interactions. Substitution of basic for hydrophobic residues in the region that overlays with phospholipid binding in related pleckstrin homology domains, however, suggests that ISPs do not retain phospholipid binding activity. Consistent with this observation, biochemical assays revealed no phospholipid binding activity. Interestingly, mapping of conserved surface residues combined with crystal packing analysis indicates that TgISPs have functionally repurposed the phospholipid-binding site likely to coordinate protein partners. Recruitment of larger protein complexes may also be aided through avidity-enhanced interactions resulting from multimerization of the ISPs. Overall, we propose a model where TgISPs recruit protein partners to the IMC to ensure correct progression of daughter cell formation.
PDB ID: 4CHMDownload
MMDB ID: 118975
PDB Deposition Date: 2013/12/3
Updated in MMDB: 2014/08
Experimental Method:
x-ray diffraction
Resolution: 2.1  Å
Source Organism:
Similar Structures:
Biological Unit for 4CHM: monomeric; determined by author
Molecular Components in 4CHM
Label Count Molecule
Protein (1 molecule)
1
IMC Sub-compartment Protein Isp1
Molecule annotation
Chemicals (4 molecules)
1
4
* Click molecule labels to explore molecular sequence information.

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