Annotation

Description

Toxoplasma gondii deoxyribose phosphate aldolase-like (TgDPA, TGME49_118750) gene expresses an essential bradyzoite-specific protein during its silent infection stage. Recently, TgDPA has been reported to interact with and enhance the activity of Toxoplasma actin depolymerizing factor (TgADF), implying it may be also involved in actin turnover, cyst maintenance and the inhibition of gliding motility of encysted bradyzoites. Study of the structural of TgDPA and its interaction with TgADF will shed new light on preventing tissue cyst formation and parasite re-emergence in immunocompromised patients. To gain a deeper understanding of this bradyzoite-specific protein, we have determined the crystal structure of the TgDPA(6-281) construct using molecular replacement phasing and refined to 1.8 Å resolution. The putative catalytic site of TgDPA was identified based on multiple sequence alignment with other known deoxyribose phosphate aldolases. A sucrose molecule, used in cryoprotection, is bound in the vicinity of that site. Each chain of TgDPA resembles (α8/β8)-TIM-barrel topology with an additional N-terminal α-helix, denoted the α0-helix. TgDPA forms a dimer in the crystal with an average buried surface area of 2,700.0 Å2. At the dimerization interface, helices α7 and α8 of two the monomers form a square-shaped opening, in which the α0-helices of the two monomers are inserted. This (α0/α7/α8)2-helical bundle creates a positively charged surface, which is exposed to the same solvent area as the N-termini of TgDPA beta-strands. This positively charged surface is proposed to be TgDPA’s interaction site with TgADF. The 40-Å long α6-helix of each chain in the dimer protrudes from the compact TIM-barrel structure into the solvent, and provides additional areas for the possible protein-protein interactions.  

Functional assignment

Lyase 

Structure information

Unit cell parameters

Space Group

P 1  

Unit Cell

a=70.92Å, b=72.19Å, c=73.05Å
α=62.90, β=89.80, γ=88.85 

Solvent content

 

Matthews coefficient

 

Refinement

Data for the highest resolution shell is in parentheses.

Resolution range

29.49-1.80Å (1.85-1.80Å)  

R_all(%)

16.7 

R_work(%)

16.6 (24.1) 

R_free(%)

20.1 (26.6) 

Num. observed reflections

116431 (8155) 

Num. R_free reflections

5821 (384) 

Completeness(%)

97.3 (92.4) 

Model parameters

Num Atoms

8833  

Num Waters

927  

Num Hetatoms

1107  

Model mean isotropic B factor

32.570Ų  

RMSD bond length

0.007Å  

RMSD bond angle

1.464°  

Filename uploaded

3QYQ.pdb (uploaded on Sep 28, 2011 11:07 AM)  

Inserted

Mar 23, 2011