Abstract
Purpose: Epithelial cell adhesion molecule (EpCAM) is a dominant antigen in human colon carcinoma tissue. Topology features of this antigen are different in normal and malignant conditions; for instance, EpCAM is much less accessible to antibodies in normal cells than in cancerous tissues. Hence, EpCAM has been considered as a suitable candidate for cancer target therapy via immunotoxins (ITs) development. In this study, attention was focused on the stability assessment of anti-EpCAM-IT (anti-Ep-IT) to design a novel IT.Methods: The 3D structures of the antibody template and the toxin segment of anti-Ep-IT were retrieved from PDB. Discovery Studio3.0 was used to separate the ligands and water molecules. The antibody (Ab) fragment of anti-Ep-IT was aligned using protein blast (BLAST-p), and SWISS-MODEL database was used for Ab modeling. IT modeling was accomplished using MODELLER 9.15. Also, GROMACS 5.07 was used for molecular dynamic (MD) simulation step. Moreover, ERRAT and RAMPAGE databases were used for quality assessment of the structures.Results: BLAST-p results indicated that antibody moiety of IT has the highest E-value and query coverage scores to the monoclonal antibody (mAb) 4D5MOC-B. Modeling by SWISS-MODEL provided a reasonable template for Ab portion compared to MODELLER. The best modeled full-length IT with the lowest RMSD values was selected. Finally, RMSD plot for MD stage demonstrated constant values from 7000ps to 20000ps.Conclusion: In general, both modeling results and their quality evaluations were satisfactory for designing IT. Moreover, RMSD plot revealed that IT stability was preserved during the simulation. Overall, our findings led to modeling and simulation of the anti-Ep-IT with more structural stability.
Highlights
Discovered in 1979, epithelial cell–adhesion molecule (EpCAM, CD326), type I, transmembrane, 39– 42 kDa glycoprotein, was first described as a dominant antigen in human colon carcinoma.[1]
The nucleotide and polypeptide sequences can be divided into the following domains: the signal sequence for periplasmic expression; histidine tags; Ab complementarity-determining regions (CDR) 1, 2, and 3 domains; VL domain; VH domain; linkers; exotoxin A (ETA) domains II, Ib, III; and an endoplasmic reticulum (ER) retention signal KDEL
An interesting feature of the model proposed for ETA is an extended cleft in domain III, and the active site of the enzyme is within this cleft
Summary
Discovered in 1979, epithelial cell–adhesion molecule (EpCAM, CD326), type I, transmembrane, 39– 42 kDa glycoprotein, was first described as a dominant antigen in human colon carcinoma.[1].
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