Antigenicity

L-Arginase, hydrolyzing L-arginine to L-ornithine
and urea, is a powerful anticancer, L-arginine-depleting
agent, against argininosuccinate synthase expressing tumors.
Otherwise, the higher antigenicity and lower thermal stability
of this enzyme was the main biochemical hurdles. Since, the
intrinsic thermal stability of enzymes follow the physiological
temperature of their producer, thus, characterization of Larginase
from thermotolerant Penicillium chrysogenum was
the objective of this study. L-Arginase (Arg) was purified to
its homogeneity from P. chrysogenum by 10.1-fold, with
37.0 kDa under denaturing PAGE, optimum reaction at
50 C, pH stability (6.8–7.9), with highest molar ratio of
constitutional arginine, glutamic acid, lysine and aspartic
acid. The purified enzyme was PEGylated and immobilized
on chitosan, with 41.9 and 22.1 % yield of immobilization.
At 40 C, the T1/2 value of free-Arg, PEG-Arg and Chit-Arg
was 10.4, 15.6, 20.5 h, respectively. The free-Arg and Chit-
Arg have a higher affinity to L-arginine (Km 4.8 mM), while,
PEG-Arg affinity was decreased by about 3 fold (Km
15.2 mM). The inhibitory constants to the free and PEG-Arg
were relatively similar towards HA and PPG. The IC50 for
the free enzyme against HEPG-2 and A549 tumor cells was
0.136 and 0.165 U/ml, comparing to 0.232 and 0.496 U/ml
for PEG-Arg, respectively. The in vivo T1/2 to the free Arg and PEG-Arg was 16.4 and 20.4 h, respectively as holoenzyme.
The residual L-arginine level upon using free Arg
was 156.9 and 144.5 lM, after 6 and 8 h, respectively,
regarding to initials at 253.6 lM, while for Peg-Arg the level
of L-arginine was nil till 7 h of initial dosing. The titer of IgG
was induced by 10–15 % in response to free-Arg after
28 days comparing to IgG titer for PEG-Arg.

Toxoplasma gondii, one of the extensively studied Apicomplexan parasites, is prevalent worldwide in animals and humans. Apart from its nuclear genome, T. gondii contains an apicoplast genome in 35 kb length which is originated from a secondary endosymbiotic event. In this study, we aimed to investigate the antigenic potential of apicoplast genome encoded proteins (n:28) of T. gondii using in silico analysis. For this purpose, proteins were primarily predicted to reveal antigenic probability and then, several bioinformatics analyses were applied for all predicted antigenic apicoplast proteins to analyze physico-chemical parameters, subcellular localization and transmembrane domain. Also, further prediction analyses including structural, B cell and MHC-I/II epitope sites as well as post-translational modifications were performed for antigenic proteins that have a signal peptide or a high antigenicity value. Of the 28 apicoplast proteins, 19 were predicted as probable antigen. Among antigenic proteins, ribosomal protein S5, L11 and S2 were predicted to have signal peptide whereas ribosomal protein L36 and S17 were predicted to have a significantly high antigenicity value (P < 0.05). In addition, ribosomal protein S5, L11, S2, L36 and S17 were predicted to have a lot of epitopes which have low IC50 and percentile rank value indicating a strong binding among epitopes and MHC-I/II alleles, and post-translational modifications such as N-linked glycosylation, acetylation and phosphorylation. To the best of authors' knowledge this is the first study to show the antigenic potential and other properties of apicoplast-derived proteins of T. gondii.