Altered stereostructures of the DNA binding domains in the mutant mating proteins of Ophiocordyceps sinensis and the Cordyceps sinensis insect-fungal complex

The MATalpha_HMGbox and HMG-box_ROX1-like domains of MAT1-1-1 and MAT1-2-1 proteins, respectively, play essential roles in DNA binding and downstream gene transcription regulation, controlling sexual reproduction of Ophiocordyceps sinensis. Alternative splicing, differential occurrence and transcription of the MAT1-1-1 and MAT1-2-1 genes have been unveiled in Hirsutella sinensis, suggesting the occurrence of self-sterility under heterothallic or hybrid outcrossing. This study further demonstrated that the MATalpha_HMGbox domains of MAT1-1-1 proteins in the wild-type Cordyceps sinensis isolates were clustered into 5 clades with or without branches in the Bayesian clustering tree, belonging to diverse 3D structural morphs under 19 AlphaFold codes. The HMG-box_ROX1-like domains of MAT1-2-1 proteins were clustered into 2 clades with branches in the Bayesian clustering tree, belonging to diverse 3D structural morphs under 25 AlphaFold codes. The correlation analysis reviewed that the 1-3 amino acid substitutions occurred in various sites of the DNA binding domains of the mutant mating proteins resulted in alteration of the hydrophobicity, secondary and tertiary structures of the DNA binding domains of the proteins. The fungal origin analysis demonstrated heterospecific fungal or genome-independent genotypical sources of the mating proteins with stereostructure variations in the wild-type C. sinensis isolates and O. sinensis strains, which represent the changed functionalities of the proteins in regulating and ensuring the accuracy and genetic diversity of the heterothallic or hybrid sexual reproductive process of O. sinensis in the lifecycle of C. sinensis insect-fungi complex.