Molecular interactions of trichoderma β-1,4-glucosidase (ThBglT12) with mycelial cell wall components of phytopathogenic Macrophomina phaseolina

Abstract

Efficacy of a β-1,4-glucosidase from Trichoderma harzianum T12 (ThBglT12) in disrupting the cell wall of the phytopathogenic fungus M. phaseolina (Macrophomina phaseolina) was studied, as the underlying molecular mechanisms of cell wall recognition remains elusive. In this study, the binding location identified by a consensus of residues predicted by COACH tool, blind docking, and multiple sequence alignment revealed that molecular recognition by ThBglT12 occurred through interactions between the α-1,3-glucan, β-1,3-glucan, β-1,3/1,4-glucan, and chitin components of M. phaseolina, with corresponding binding energies of −7.4, −7.6, −7.5 and −7.8 kcal/mol. The residue consensus verified the participation of Glu172, Tyr304, Trp345, Glu373, Glu430, and Trp431 in the active site pocket of ThBglT12 to bind the ligands, of which Trp345 was the common interacting residue. Root mean square deviation (RMSD), root mean square fluctuation (RMSF), total energy, and minimum distance calculation from molecular dynamics (MD) simulation further confirmed the stability and the closeness of the binding ligands into the ThBglT12 active site pocket. The h-bond occupancy by Glu373 and Trp431 instated the role of the nucleophile for substrate recognition and specificity, crucial for cleaving the β-1,4 linkage. Further investigation showed that the proximity of Glu373 to the anomeric carbon of β-1,3/1,4-glucan (3.5 Å) and chitin (5.5 Å) indicates the nucleophiles’ readiness to form enzyme-substrate intermediates. Plus, the neighboring water molecule appeared to be correctly positioned and oriented towards the anomeric carbon to hydrolyze the β-1,3/1,4-glucan and chitin, in less than 4.0 Å. In a nutshell, the study verified that the ThBglT12 is a good alternative fungicide to inhibit the growth of M. phaseolina.

Communicated by Ramaswamy H. Sarma

Keywords:

• Trichoderma harzianum T12
• Macrophomina phaseolina
• β-1,4-glucosidase
• β-1,3/1,4-glucan
• chitin
• molecular docking

Disclosure statement

No potential conflict of interest was reported by the authors.

Figure 11. The distance between Glu172 and the water molecule in the presence of β-1,3/1,4-glucan (A), chitin (B), α-1,3-glucan(C) and β-1,3-glucan (D).

Figure 12. The distance between the water molecule and the anomeric carbon of β-1,3/1,4-glucan (A), chitin (B), α-1,3-glucan(C), and β-1,3-glucan (D).

Figure 13. The angle of Glu172-water molecule-anomeric carbon of β-1,3/1,4-glucan.

Figure 14. Comparison of average binding free energy for α-1,3-glucan, β-1,3-glucan, β-1,3/1,4-glucan, and chitin for the last 25 ns of the simulation.

Additional information

Funding

This research was supported by the International Islamic University Malaysia through Research Initiative Grant Scheme (RIGS-17-089-0664) and Research Management Center-Sustainable Development Goals grant (RMCG20-002-0002).