The chitinolytic enzymes from the entomopathogenic fungus Metarhizium anisopliae: GH family distribution, domain architecture, and protein regulation

<i>Metarhizium anisopliae</i> is an entomopathogenic fungus that is widely used in the biological control of agricultural pests. During host infection, <i>M. anisopliae</i> secretes an arsenal of hydrolytic enzymes such as proteases and chitinases that allow for cuticle penetration and host colonization. The degradation of chitin into N-acetylglucosamine (GlcNAc) monomers is carried out by chitinases and β-N-acetylglucosaminidases (NAGases). Chitin-degrading enzymes of <i>M. anisopliae</i> have been the subject of extensive research; however, these studies have not been consolidated into a comprehensive review. This review highlights our current knowledge of the chitinolytic enzymes from <i>M. anisopliae</i>, emphasizing the classification of these enzymes based on their mode of action and domain architecture. <i>M. anisopliae</i> possesses a set of 21 chitinases that are classified into four glycoside hydrolase family 18 (GH18) subgroups: A, B, C, and D. In addition, <i>M. anisopliae</i> produces two GH20 and two GH3 NAGases. The domain architectures of chitinases and NAGases from <i>M. anisopliae</i> are highly similar to those found in <i>Trichoderma</i> spp. but exhibit some evolutionary distinctions. Moreover, this review integrates insights from other entomopathogenic fungi to identify molecular mechanisms underlying the expression of chitinase and NAGase genes in <i>M. anisopliae</i>. The regulatory mechanisms underlying gene expression of chitinolytic enzymes are complex and involve several regulators and metabolic pathways. Finally, chitinases have the potential to be used as biopesticides against fungal pathogens and pest infestations.