Relationship Between Structure And Anti-liver Cancer Activity Of Parasporin-2

Bacillus thuringiensis (Bt), an ubiquitous gram-positive spore-forming bacteriumforms parasporal proteins during the stationary phase of its growth. Bt is a promisingmicrobial agent in the control of insect pests in agriculture, forestry, veterinary andpublic health management. Recent findings of selective human cancer cell-killingactivity in non-insecticidal Bt isolates resulted in a new category of Bt parasporalprotein called Parasporin. At present, six Parasporins have been found. Parasporin-2is one of those Parasporins.Mutations were introduced in anticancer parasporal crystal protein (named P2Y),which produced nine mutated parasporal crystal protein (named P11, P12, P13, P14,p21, P22, P31, P32and P33, separatly). This nine mutated proteins’ semi-lethal dose(LD50) of liver cancer cells vary greatly: the minimum is0.96μg/mL while themaximum is37.29μg/mL (for P12and P32, the LD50value are2.04μg/mL and0.96μg/mL, separately). Thus, we speculated that there should be a certain correlationbetween the amino acid compostion of these nine mutants and its anti-hepatomaactivity.Therefore we took the following analysis and research.Homology modeling was employed to build a model of3D-structure of P11, P32and P2Y.Then secondary structure and tertiary structure comparison of P11, P32wereconducted and the result indicated that β-sheet, β-fold becoming longer or increasingthe amount of ɑ-spiral would affect the anti-cancer activity of Parasporins. These nineproteins have3to7mutated amino acids, and most of them were located at the site of32,131,217,225and242after amino acid blasting.In order to explore the relationship between Parasporin amino acid sequence and itsanti-cancer activity, the amino acid sequence analysis, protein-protein docking,Optimal Docking Area (ODA) and other experiments were carried out. Hereglyceraldehyde-3-phosphate dehydrogenase (GAPDH) was taken as a new receptorprotein of anti-cancer parasporal crystal protein family. And the results were found asfollow: Mutant P11and P32had the lowest binding energy value, consisted with the anticancer activity tests in human cancer cells.Amino acid residues at the site of49,51,52,55-60,194, and205-212on Parasporin are highly involved in protein-proteininteractions, especially the aromatic amino acids such as tryptophan (W), tyrosine (Y),phenylalanine (F).This study identified three key amino acids and four amino sites which areimportant to the anticancer activities of parasporal crystal protein.Theoretically, thesefindings reveal the relationship between Parasporin-2amino acid sequence and itsanti-hepatoma activity. And it may help to synthesize new Parasporin-2with highcancer-killing activity.