Identification of Novel Inhibitors of Starch Excess 4 (SEX4)

This study identified several inhibitors of Starch Excess 4 (SEX4), an enzyme in plants' starch decomposition. Our research aims to inhibit starch breakdown by SEX4 with its potential to significantly impact food security, leading to starch accumulation in plants such as potatoes, sweet potatoes, and significant crops like grains and rice. We recognized potential candidates by screening approximately 1840 chemical compounds using the phosphatase assay against <i>p</i>NPP. The IC₅₀ values of the selected candidates were determined through the <i>p</i>NPP assay and the amylopectin assay, while K_i values were confirmed by calculating V_max, K_M, and <i>k</i>_cat values. Finally, we compared the IC₅₀ values of Like Sex Four 2 (LSF2) and SEX4 to assess their selectivity. This screening yielded several potential inhibitory compounds, with F05 showing promise in the <i>p</i>NPP assay and F09 and G11 in the amylopectin assay, all demonstrating more selectivity for SEX4 than LSF2. Consequently, we identified seven chemicals as promising inhibitor compounds, offering potential for future research and applications. However, further quantitative structure-activity relationship studies and the practical application to test selected compounds on crops will be necessary in future research.