Computational modeling and functional characterization of a GgChi: A class III chitinase from corms of Gladiolus grandiflorus

• Published in: The Kaohsiung journal of medical sciences 2018-12, Vol.34 (12), p.673-683
• Main Authors: Rafiq, Maria, Hussain, Ashiq, Shah, Kausar Hussain, Saeed, Qamar, Sial, Muhammad Umair, Ali, Zahid, Buck, Friedrich, Goodman, Richard E., Khaliq, Binish, Ishaq, Uzma, Baig, Mirza Ahsen, Munawar, Aisha, Mahmood, Seema, Akrem, Ahmed
• Format: Article
• Language: English
• Subjects: Antibacterial; Antifungal; Endochitinase; Gladiolus grandiflorus; TIM barrel
• ISSN: 1607-551X; 2410-8650
• DOI: 10.1016/j.kjms.2018.08.003

The present study describes the predicted model and functional characterization of an endochitinase (30 kDa) from corms of Gladiolus grandiflorus. ESI-QTOF-MS generated peptide showed 96% sequence homology with family 18, Class III acidic endochitinase of Gladiolus gandavensis. Purified G. grandiflorus chitinase (GgChi) hydrolyzed 4-methylumbelliferyl β-d-N,N′,N′′-triacetylchitotriose substrate showing specific endochitinase activity. Since no structural details of GgChi were available in the Protein Data Bank (PDB), a homology model was predicted using the coordinate information of Crocus vernus chitinase (PDB ID: 3SIM). Ramachandran plot indicated 84.5% in most favored region, 14.8% in additional and 0.6% in generously allowed region while no residue in disallowed region. The predicted structure indicated a highly conserved (β/α)8 (TIM barrel) structure similar to the family 18, class III chitinases. The GgChi also showed sequence and structural homologies with other active chitinases. The GgChi (50 μg/disc) showed no antibacterial activity, but did provide mild growth inhibition of phytopathogenic fungus Fusarium oxysporum at a concentration of 500 μg/well Similarly, insect toxicity bioassays of GgChi (50 μg) against nymphs of Bemisia tabaci showed 14% reduction in adult emergence and 14% increase in mortality rate in comparison to control values. The GgChi (1.5 mg) protein showed significant reduction in a population of flour beetle (Tribolium castaneum) after 35 days, but lower reactivity against rice weevil (Sitophilus oryzae). The results of this study provide detai.led insight on functional characterization of a family 18 class III acidic plant endochitinase.