One of the best-studied gene families related to plant defense mechanisms encode proteins known as PR-1. These proteins play an important role during pathogen-host interactions, can block the development of fungi and are systemic acquired resistance markers. Interestingly, PR-1 are members of the SCP/TAPS protein superfamily, which are expressed by pathogenic nematodes and have immunomodulatory effects by suppressing host defense responses. Recently, it was found that SCP/TAPS proteins are capable of transporting cholesterol across the cell membrane and bind to fatty acids and steroid molecules through the Caveolin Binding Motif (CBM). Furthermore, it was shown that SCP/TAPS proteins bind to hydrophobic plant-derived antifungal molecules and inhibit their antifungal activity. Notably, previous results from our group indicate that MpPR-1k from Moniliophthora perniciosa may have the ability to selectively export cholesterol, while MpPR-1i does not bind to cholesterol, but binds to palmitate. This was traced to the CBM, and we were able to interchange the ligand selectivity of MpPR-1k and MpPR-1i through site-directed muthagenesis. Thus, the objective of this project is to structurally characterize MpPR1-i and MpPR1-k through X-ray crystallography, aiming at better understanding the features necessary for ligand interaction and selectivity. This will be achieved through the crystallization and comparison of wild type and mutated versions of MpPR-1k and MpPR1-i. We intend to understand more closely the mechanisms of action of these proteins in the plant-pathogen interaction, and especially during the interaction of M. perniciosa-cacao.
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