*Article* **Combined Protein and Alkaloid Research of** *Chelidonium majus* **Latex Reveals CmMLP1 Accompanied by Alkaloids with Cytotoxic Potential to Human Cervical Carcinoma Cells**

**Robert Nawrot 1,\* , Alicja Warowicka 2,3 , Piotr Józef Rudzki <sup>4</sup> , Oskar Musidlak <sup>1</sup> , Katarzyna Magdalena Dolata 1,†, Jacek Musijowski <sup>4</sup> , Elzbieta Urszula Stolarczyk ˙ 4,‡ and Anna Go´zdzicka-Józefiak <sup>1</sup>**


**Abstract:** *Chelidonium majus* L. is a latex-bearing plant used in traditional folk medicine to treat human papillomavirus (HPV)-caused warts, papillae, and condylomas. Its latex and extracts are rich in many low-molecular compounds and proteins, but there is little or no information on their potential interaction. We describe the isolation and identification of a novel major latex protein (CmMLP1) composed of 147 amino acids and present a model of its structure containing a conserved hydrophobic cavity with high affinity to berberine, 8-hydroxycheleritrine, and dihydroberberine. CmMLP1 and the accompanying three alkaloids were present in the eluted chromatographic fractions of latex. They decreased in vitro viability of human cervical cancer cells (HPV-negative and HPV-positive). We combined, for the first time, research on macromolecular and low-molecular-weight compounds of latex-bearing plants in contrast to other studies that investigated proteins and alkaloids separately. The observed interaction between latex protein and alkaloids may influence our knowledge on plant defense. The proposed toolbox may help in further understanding of plant disease resistance and in pharmacological research.

**Keywords:** major latex protein; *Chelidonium majus*; greater celandine; defense-related proteins; alkaloids; molecular docking; cancer cells
