Abstract
An obligate mutualistic relationship exists between the fungus Amylostereum areolatum and woodwasp Sirex noctilio. The fungus digests lignin in the host pine, providing essential nutrients for the growing woodwasp larvae. However, the functional properties of this symbiosis are poorly described. In this study, we identified, cloned, and characterized 14 laccase genes from A. areolatum. These genes encoded proteins of 508 to 529 amino acids and contained three typical copper-oxidase domains, necessary to confer laccase activity. Besides, we performed molecular docking and dynamics simulation of the laccase proteins in complex with lignin compounds (monomers, dimers, trimers, and tetramers). AaLac2, AaLac3, AaLac6, AaLac8, and AaLac10 were found that had low binding energies with all lignin model compounds tested and three of them could maintain stability when binding to these compounds. Among these complexes, amino acid residues ALA, GLN, LEU, PHE, PRO, and SER were commonly present. Our study reveals the molecular basis of A. areolatum laccases interacting with lignin, which is essential for understanding how the fungus provides nutrients to S. noctilio. These findings might also provide guidance for the control of S. noctilio by informing the design of enzyme mutants that could reduce the efficiency of lignin degradation.
Highlights
The European woodwasp, Sirex noctilio Fabricius (Hymenoptera; Symphyta; Siricidae), is an important pest that causes considerable economic and ecological damage globally [1]
Like most wood-decay fungi, A. areolatum produces a large number of enzymes to digest all compounds of pine wood in xylem tissues, which provides a primary source of nutrition for the woodwasp larvae [16,18,19,20,21]
We investigated the molecular interactions for binding between laccases and lignin compounds and found that hydrogen bonding and hydrophobic interactions were present
Summary
The European woodwasp, Sirex noctilio Fabricius (Hymenoptera; Symphyta; Siricidae), is an important pest that causes considerable economic and ecological damage globally [1]. PPhhyyllooggeenneettiicc ttrreeeess,, mmoottiiff,, ddoommaaiinn aanndd ggeennee ssttrruuccttuurree ooff AA.. Hydrogen-bond interactions, together with hydrophobic contacts, were found necessary to the interactions of lignin model compounds with Lac proteins. Strong hydrogen bonds were formed between lignin model compounds and the laccase proteins AaLac, Int. J. Strong hydrogen bonds were formed between lignin model compounds and the laccase proteins AaLac, AaLac, AaLac, AaLac, AaLac, AaLac, and AaLac (Figure 6). We found that the lignin model compounds formed hydrophobic interactions with amino acids around the laccase binding site. When looking at the active sites of laccase proteins, we found that 18 amino acid residues, namely, ALA, ARG, ASN, ASP, GLN, GLU, GLY, HIS, ILE, LEU, LYS, PHE, PRO, SER, THR, TRP, TYR, and VAL, were involved in the hydrogen bonding and hydrophobic interactions of the docked complexes (Table S3). We observed that in some laccases, monomers, dimer, and trimer (tetramer) bound at the same pocket, while the other tetramer (trimer) bound separately at different pocket (Figure 6 and Figures S4–S10)
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