A novel plastocyanin-like protein from <i>Strobilanthes schomburgkii</i> (Craib) J.R.I.Wood leaves: isolation and anti-inflammatory activity through MAPK signalling

<i>Strobilanthes schomburgkii</i> (Craib) J.R.I. Wood, a member of the Acanthaceae family, is a traditional medicinal plant with a wide range of therapeutic uses. Extracts of this plant have been employed for wound healing, as well as to treat and prevent various diseases, including inflammation, acute and chronic colitis, digestive disorders, bloating, diarrhoea, hemostasis, and cancer. In this study, plastocyanin-like protein (<b>SSW</b>) from the leaves of <i>S. schomburgkii</i> was isolated and evaluated for its anti-inflammatory activity. The <b>SSW</b> protein showed an approximate molecular mass of 15 kDa according to Tricine-SDS-PAGE. N-terminal sequence of the protein (<b>FEVLMGSDVGELVFXP</b>) shared 70-80% similarity with plastocyanin-like proteins from plants. Our results suggest that <b>SSW</b> represents a novel member of the plastocyanin-like protein family. <b>SSW</b> inhibited bovine serum albumin (BSA) denaturation with an IC₅₀ of 0.399 mg/mL, exhibiting activity similar to diclofenac, a non-steroidal anti-inflammatory drug. At a concentration of 40 µg/mL, the <b>SSW</b> did not exhibit any cytotoxic effects and suppressed cytokine production on macrophages <i>in vitro</i> as effectively as dexamethasone. A strong anti-inflammatory activity of <b>SSW (</b>40 µg/mL) was associated with inhibition of mitogen-activated protein kinase (MAPK) signalling pathways in macrophages, that lead to the significant decrease of the extracellular signal-regulated kinase (P-ERK) and p38 phosphorylation. Therefore anti-inflammatory properties of <i>S. schomburgkii</i> leaves, revealed by Vietnam folk medicine, are at least partially mediated by plastocyanin-like protein of this plant.