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The structural landscape and diversity of Pyricularia oryzae MAX effectors revisited
Mounia Lahfa1, Philippe Barthe1, Karine de Guillen1
1Centre de Biologie Structurale, Univ Montpellier, CNRS UMR 5048, INSERM U 1054, Montpellier, France.
Abstract:
Magnaporthe AVRs and ToxB-like (MAX) effectors constitute a family of secreted virulence proteins in the fungus Pyricularia oryzae (syn. Magnaporthe oryzae), which causes blast disease on numerous cereals and grasses. In spite of high sequence divergence, MAX effectors share a common fold characterized by a ß-sandwich core stabilized by a conserved disulfide bond. In this study, we investigated the structural landscape and diversity within the MAX effector repertoire of P. oryzae. Combining experimental protein structure determination and in silico structure modeling we validated the presence of the conserved MAX effector core domain in 77 out of 94 groups of orthologs (OG) identified in a previous population genomic study. Four novel MAX effector structures determined by NMR were in remarkably good agreement with AlphaFold2 (AF2) predictions. Based on the comparison of the AF2-generated 3D models we propose a classification of the MAX effectors superfamily in 20 structural groups that vary in the canonical MAX fold, disulfide bond patterns, and additional secondary structures in N- and C-terminal extensions. About one-third of the MAX family members remain singletons, without strong structural relationship to other MAX effectors. Analysis of the surface properties of the AF2 MAX models also highlights the high variability within the MAX family at the structural level, potentially reflecting the wide diversity of their virulence functions and host targets.
Insights
Magnaporthe AVRs and ToxB-like (MAX) effectors from Pyricularia oryzae show diverse structures despite sequence divergence. This study classifies MAX effectors into 20 groups, revealing structural variations that may explain their varied functions in plant diseases.
Area of Science:
- Fungal Pathogenesis
- Structural Biology
- Genomics
Background:
- Magnaporthe AVRs and ToxB-like (MAX) effectors are secreted virulence proteins in Pyricularia oryzae, the causal agent of devastating blast disease in cereals.
- Despite significant sequence divergence, MAX effectors share a conserved structural core, a ß-sandwich fold stabilized by a disulfide bond.
Purpose of the Study:
- To investigate the structural diversity and landscape of the MAX effector repertoire in Pyricularia oryzae.
- To classify the MAX effector superfamily based on structural features and variations.
Main Methods:
- Combined experimental methods (NMR) for protein structure determination with in silico structure modeling (AlphaFold2).
- Validated conserved MAX effector core domains in identified orthologous groups (OGs).
- Classified MAX effectors into structural groups by comparing AlphaFold2-generated 3D models.
Main Results:
- Confirmed the conserved MAX effector core domain in 77 out of 94 previously identified OGs.
- Experimental NMR structures closely matched AlphaFold2 predictions, validating the in silico approach.
- Proposed a classification of the MAX effector superfamily into 20 distinct structural groups.
- Identified significant structural variability in N- and C-terminal extensions and disulfide bond patterns.
- Approximately one-third of MAX effectors were identified as singletons with limited structural similarity to others.
- Surface property analysis of MAX models indicated high structural variability.
Conclusions:
- The study successfully characterized the structural diversity within the MAX effector family of Pyricularia oryzae.
- A novel classification system for MAX effectors based on structural features was established.
- The observed structural variability suggests a wide range of functions and host targets for MAX effectors in fungal virulence.
