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                                                RICIN

INTRODUCTION

  Ricin is a potent cytotoxin that is synthesized in the edosperm 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 Inactivating 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).

FUNCTION

  The mechanism employed by Ricin to gain entry to a host cell involves 

the heterodimeric properties of 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 this happens the B chain can fascilitate the transfer of the A chain into the Cytoplasm(2). This association between A and B chain is essential for toxicity(2) without it the Ricin would not be able to gain access to the cells organelles. Once the A chain gains entry into the cytosol its target of attack is the ribosome, and its mechanism involves depurination of a single endenosine residue in 28S ribosome RNA(3); which

inhibits ribosome function, thus stopping protein synthesis.

Please do NOT make changes to this Sandbox until after April 23, 2010. Sandboxes 151-200 are reserved until then for use by the Chemistry 307 class at UNBC taught by Prof. Andrea Gorrell.