Hortensin 4, main type 1 ribosome inactivating protein from red mountain spinach seeds: Structural characterization and biological action

Here, we report the primary structure of hortensin 4, main type 1 ribosome inactivating protein (RIP) isolated from Atriplex hortensis seeds. The complete sequencing was achieved by a combination of mass spectrometry coupled with Edman degradation. The amino acid sequence of hortensin 4 matches with that of Atriplex patens type 1 RIP, deduced from the cDNA sequence (AC: ABJ90432.1). The protein consists of 254 amino acid residues, without cysteinyl residues and a N-Acetylhexosamine chain at position Asn231. Structural studies (CD spectrum and 3D model) show a protein core typical of RIPs, and the amino acid residues of active site are conserved. In addition, to get insight into the protective effects of hortensin 4 against pathogens and its putative biotechnological applications, we evaluated the: i) N-glycosylase activity against the tobacco mosaic virus (TMV) RNA; (ii) antifungal activity towards Trichoderma harzianum and Botrytis cinerea, by damaging fungal ribosomes; and (iii) inhibition of human primary glioblastoma NULU cells proliferation, with cytotoxicity enhanced in the presence of temozolomide, used as a chemotherapeutic agent. Altogether, the multiple biological activities of hortensin 4 could be exploited both to improve the resistance to various pathogens by engineering transgenic plants and to develop useful tools for cancer therapy.