Abstract
Ricin is a heterodimeric plant protein that is potently toxic to mammalian and many other eukaryotic cells. It is synthesized and stored in the endosperm cells of maturing Ricinus communis seeds (castor beans). The ricin family has two major members, both, lectins, collectively known as Ricinus communis agglutinin ll (ricin) and Ricinus communis agglutinin l (RCA). These proteins are stored in vacuoles within the endosperm cells of mature Ricinus seeds and they are rapidly broken down by hydrolysis during the early stages of post-germinative growth. Both ricin and RCA traffic within the plant cell from their site of synthesis to the storage vacuoles, and when they intoxicate mammalian cells they traffic from outside the cell to their site of action. In this review we will consider both of these trafficking routes.
Highlights
Ricin and Ricinus communis agglutinin l (RCA) are galactose-specific lectins, each possessing at least two sugar binding sites
We know that the agglutination he observed is largely due to RCA, which is a Toxins 2011, 3 strong haemagglutinin but a weak cytotoxin, whereas ricin is a weak haemagglutinin but is potently cytotoxic [2,3]
Ricin and RCA are synthesized in the seeds at the developmental stage when seed storage proteins are being synthesized and, like these storage proteins, the lectins are located in the storage vacuoles of the mature seed [13,14]
Summary
Ricin and RCA are galactose-specific lectins, each possessing at least two sugar binding sites. A PhD student at the University of Dorpat in Estonia, was looking for an explanation for the well known toxicity of Ricinus seed extracts He studied the effects of mixing seed extract with blood and observed that the red blood cells began to agglutinate. We know that the agglutination he observed is largely due to RCA, which is a Toxins 2011, 3 strong haemagglutinin but a weak cytotoxin, whereas ricin is a weak haemagglutinin but is potently cytotoxic [2,3]. Since RTA-modified ribosomes are unable to bind these translation factors they are no longer capable of continuing protein synthesis This leads to cell death and accounts for the extreme cytotoxicity of ricin [6,7,8]. ~128 kDa tetrameric RCA with the subunit arrangement B-A-A-B [11,12]
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