Discovery of a "first-in-class" plant-derived cystine-stabilized proteasome inhibitor

Abstract

Cysteine-rich peptides (CRPs) are a group of underexplored compounds between 2 – 8 kDa. Hibiscus sabdariffa was found to be a rich source of CRPs which were named as roseltides. Thus far, eight roseltides rT1 – rT8 have been identified. Roseltide rT1 was previously characterized as a knottin-type human neutrophil elastase inhibitor. The second most abundant, roseltide rT7 however, have not been characterized. In this study, we aim to chemically synthesize and functionally characterize roseltide rT7. Here we report the successful synthesis of roseltide rT7 using automated solid-phase peptide synthesis followed by oxidative folding of the linear peptide into its native conformation. Using chemical labeling, we successfully obtained TAMRA-rT7 which displayed cell-penetrating properties in flow cytometry and confocal microscopy analyses. Sequence motif search revealed roseltide rT7 shared sequence similarity to PR-39, a cell-penetrating proteasome inhibitor with pro-angiogenic properties. Likewise in this study, roseltide rT7 was found to be a 20S proteasome inhibitor and possess pro-angiogenic properties. To the best of our knowledge, roseltide rT7 is a “first-in-class” cystine-stabilized proteasome inhibitor with pro-angiogenic properties.