Ricin

From Proteopedia

Revision as of 03:13, 31 March 2010

                                                RICIN
                                                   

INTRODUCTION

Ricin is a potent cytotoxi that is synthesized in the endosperm cells of maturing Riccinus seeds(1). Ricin belongs to a small multi gene family(2) that is composed of eight members. It is also important to mention that Ricin is classified as a type II heterodimeric Ribosome Inactivatiing protein(1).

STRUCTURE

Ricin is a heterodimer that consists of a 32,000 Dalton A chain glycoprotein linked by a disulfide bond to a 32,000 Dalton B chain glycoprotein(2). The A chain enzyme is a globular protein with extensive secondary structure and a predominate active site(2); where the B chain is a lectin(2) that binds to galactose-containing surface receptors(3).

PHYSIOLOGY

The mechanism deployed by Ricin to gain entry to a host cell uses the heterogenic properties given to the toxin. Firstly the toxin arranges itself in such a way where its B chain can easily interact with the host cells receptors, and once acknowledgement happens, the B chain can fascilitate transport of the A chain into the cytoplasm(2). This association between the A and B chain is essential for toxicity(2) without it the Ricin would not be able to gain access to the cells organelles rendering it useless. Once the A chain gains entry into the cytosol its mechanism for attack of the ribosome is depurination of a single endenosine residue in 28S Ribosomal RNA(3) and this inhibits protein synthesis.

1. Lord, Michael J., Roberts, Lynne M., Robertus, Jon D. Ricin: structure, mode of action, and some current applications. The FSEB journal. Vol 8. 1994. 2. Ernst, Stephen R., Hamlin, Ron., Katsen, Betsy., Montfort, William., Monzingo, Arthur F., Robertus, Jon D., Rutenbur, Earl., Villafranca, Jesus E., Xuong, Nuyhen H. The Three Dimensional Structure of Ricin at 2.8 Angstrom. The Journal of Biological Chemistry. Vol 262, No 11, pp. 5398-5403.1987.