Type 1 Ribosome-Inactivating Proteins from the Ombu ´ Tree (Phytolacca dioica L.) Augusto Parente, Rita Berisio, Angela Chambery, and Antimo Di Maro Abstract The toxicity of plant proteins, later identified as ribosome-inactivating proteins (RIPs), was described more than a century ago and their enzymatic activity was established more than 30 years ago. However, their physiological role and related biological activities are still uncertain. Therefore, despite the body of literature, research on RIPs is ongoing. This review deals with new RIPs being purified, sequenced, characterized, and cloned, and an increasing number of 3D-structures that are determined at high resolution. This is the case of the five type 1 RIPs (PD-S1-3, PD-L1/2, PD-L3/4, dioicin 1, and dioicin 2) from seeds and leaves of the ombu ´ tree (Phytolacca dioica L.), native of the grassy pampas of Argentina. The data collected so far will contribute to our understanding of impor- tant issues of RIP research: (1) identifying structural determinants responsible for new enzymatic activities such as the DNA cleaving activity; (2) glycosylation and its influence on the catalytic and biological activities; (3) cellular localization of endogenous RIPs and their physiological role(s). 1 Introduction Ribosome-inactivating proteins (RIPs; rRNA N-b-glycosidases; EC 3.2.2.22) have been isolated from a number of higher plants; fungi, bacteria, and at least one alga (Girbe ´s et al. 2004). The genus Phytolacca (Fam. Phytolaccaceae) has several tens A. Parente (*), A. Chambery, and A.D. Maro Department of Life Sciences, Second University of Naples, Italy e-mail: augusto.parente@unina2.it R. Berisio Department of General Chemistry, University of Naples Federico II, Italy J.M. Lord and M.R. Hartley (eds.), Toxic Plant Proteins, Plant Cell Monographs 18, DOI 10.1007/978-3-642-12176-0_5, # Springer-Verlag Berlin Heidelberg 2010 79