Saporin
Encyclopedia
Saporin is a protein
that is useful in biological
research applications, especially studies of behavior. Saporin is a so-called ribosome inactivating protein
(RIP), due to its N-glycosidase activity, from the seeds of Saponaria officinalis (common name: soapwort). It was first described by Fiorenzo Stirpe and his colleagues in 1983 (Stirpe, Gasper-Campani et al. 1983) in an article that illustrated the unusual stability of the protein.
Among the RIPs are some of the most toxic molecules known, including ricin
and abrin
(the latter is the poison preferred by the characters in The Blue Lagoon
). These toxins contain second protein strand that inserts the RIP into a cell
, making it able to enzymatically
inactivate the ribosomes, shutting down protein synthesis and resulting in cell death, and eventually causing death of the victim. Saporin has no chain capable of inserting it into the cell. Thus it and the soapwort plant are safe to handle. This has aided its use in research.
If given a method of entry into the cell, saporin becomes a very potent toxin, since its enzymatic activity is among the highest of all RIPs (Stirpe, Barbieri et al. 1992). The enzymatic activity of RIPs is unusually specific: a single adenine
base is removed from the ribosomal RNA
of the large subunit of the ribosome. This is the Achilles’ heel of the ribosome; the removal of this base completely inhibits the ability of that ribosome to participate in protein synthesis. The fungal toxin alpha-sarcin cuts the ribosomal RNA at the adjacent base, also causing protein synthesis inhibition (Hill, Dahlberg et al. 1990).
The conversion of saporin into a toxin has been used to create a series of research molecule
s. Attachment of saporin to something that enters the cell will convert it into a toxin for that cell. If the agent is specific for a single cell type, by being an antibody
specific for some molecule that is only presented on the surface of the target cell type, then a set group of cells can be removed. This has many applications, some more successful than others. Saporin is not the only molecule that is used in this way; the enzymatic chain of ricin, the RIP gelonin
, the enzymatic chain of Pseudomonas
exotoxin, the enzymatic chain of diphtheria
toxin have also been used, again with variations in success.
Immunotoxins consisting of a monoclonal antibody linked to saporin have been developed and evaluated in formal clinical trials in patients with leukaemia and lymphoma in the UK and Germany. One disadvantage of these types of immunotoxin for clinical use is their relatively narrow therapeutic window
and associated potentially life threatening toxicities at dose levels that are therapeutic. During the past 15 years the research group of Dr David Flavell
at Southampton General Hospital in the UK have been investigating various ways of improving the potency and widening the therapeutic window for saporin-based immunotoxins thereby opening up new possibilities for this class of drug. Most recently saponins (not to be confused with saporin) from Gypsophila paniculata have been show to significantly augment saporin-based immunotoxins directed against human cancer cells by several orders of magnitude.
In the last 15 years, in research begun by R.G. Wiley of Vanderbilt University
, saporin has been used mainly to target specific neuronal populations in lab animals
and eliminate them. This allows the researcher to observe the behavioral changes and associate them with the neuronal populations that were eliminated. For instance, the elimination of the cholinergic neurons of the rat basal forebrain by the toxin created by attaching saporin to an antibody that attaches to, and then internalizes into, only these neurons has created a mimic for the crucial result of Alzheimer's disease
in humans (Wenk, Stoehr et al. 1994). In this way, collateral results of the progression of the disease or drugs for the intervention can be studied. More than 300 scientific articles have been published utilizing saporin for study of the nervous systems, and more than 15 specific toxins have been created.
Saporin’s success is probably due to its stability. Santanche et al. have evaluated the physical characteristics of the protein and conclude “(t)he remarkable resistance of saporin to denaturation
and proteolysis
suggests this protein as an ideal candidate for biotechnological applications” (Santache, Bellelli et al. 1997).
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that is useful in biological
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
research applications, especially studies of behavior. Saporin is a so-called ribosome inactivating protein
Ribosome inactivating protein
A ribosome inactivating protein is a protein synthesis inhibitor that acts at the ribosome..A number of bacterial and plant toxins act by inhibiting protein synthesis in eukaryotic cells. The toxins of the Shiga and ricin family inactivate 60S ribosomal subunits by an N-glycosidic cleavage which...
(RIP), due to its N-glycosidase activity, from the seeds of Saponaria officinalis (common name: soapwort). It was first described by Fiorenzo Stirpe and his colleagues in 1983 (Stirpe, Gasper-Campani et al. 1983) in an article that illustrated the unusual stability of the protein.
Among the RIPs are some of the most toxic molecules known, including ricin
Ricin
Ricin , from the castor oil plant Ricinus communis, is a highly toxic, naturally occurring protein. A dose as small as a few grains of salt can kill an adult. The LD50 of ricin is around 22 micrograms per kilogram Ricin , from the castor oil plant Ricinus communis, is a highly toxic, naturally...
and abrin
Abrin
Abrin is a toxalbumin that is found in the seeds of a plant called lucky bean, rosary pea or jequirity pea. Abrin is similar to but far more deadly than ricin, a toxin found in the seeds of the castor oil plant.-Physical Properties:...
(the latter is the poison preferred by the characters in The Blue Lagoon
The Blue Lagoon (1980 film)
The Blue Lagoon is a 1980 American romance and adventure film directed by Randal Kleiser. The screenplay by Douglas Day Stewart was based on the novel The Blue Lagoon by Henry De Vere Stacpoole. The film stars Brooke Shields and Christopher Atkins...
). These toxins contain second protein strand that inserts the RIP into a cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
, making it able to enzymatically
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
inactivate the ribosomes, shutting down protein synthesis and resulting in cell death, and eventually causing death of the victim. Saporin has no chain capable of inserting it into the cell. Thus it and the soapwort plant are safe to handle. This has aided its use in research.
If given a method of entry into the cell, saporin becomes a very potent toxin, since its enzymatic activity is among the highest of all RIPs (Stirpe, Barbieri et al. 1992). The enzymatic activity of RIPs is unusually specific: a single adenine
Adenine
Adenine is a nucleobase with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate and the cofactors nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and protein synthesis, as a chemical component of DNA...
base is removed from the ribosomal RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
of the large subunit of the ribosome. This is the Achilles’ heel of the ribosome; the removal of this base completely inhibits the ability of that ribosome to participate in protein synthesis. The fungal toxin alpha-sarcin cuts the ribosomal RNA at the adjacent base, also causing protein synthesis inhibition (Hill, Dahlberg et al. 1990).
The conversion of saporin into a toxin has been used to create a series of research molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s. Attachment of saporin to something that enters the cell will convert it into a toxin for that cell. If the agent is specific for a single cell type, by being an antibody
Antibody
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...
specific for some molecule that is only presented on the surface of the target cell type, then a set group of cells can be removed. This has many applications, some more successful than others. Saporin is not the only molecule that is used in this way; the enzymatic chain of ricin, the RIP gelonin
Gelonin
Gelonin is a protein toxin of approximately 30 kDa found in the seeds of the Himalayan plant Gelonium multiflorum. In cell-free systems gelonin exerts powerful N-glycosidase activity on the 28S rRNA unit of eukaryotic ribosomes by cleaving out adenine at the 4324 site.-References:*Stirpe, F.,...
, the enzymatic chain of Pseudomonas
Pseudomonas
Pseudomonas is a genus of gammaproteobacteria, belonging to the family Pseudomonadaceae containing 191 validly described species.Recently, 16S rRNA sequence analysis has redefined the taxonomy of many bacterial species. As a result, the genus Pseudomonas includes strains formerly classified in the...
exotoxin, the enzymatic chain of diphtheria
Diphtheria
Diphtheria is an upper respiratory tract illness caused by Corynebacterium diphtheriae, a facultative anaerobic, Gram-positive bacterium. It is characterized by sore throat, low fever, and an adherent membrane on the tonsils, pharynx, and/or nasal cavity...
toxin have also been used, again with variations in success.
Immunotoxins consisting of a monoclonal antibody linked to saporin have been developed and evaluated in formal clinical trials in patients with leukaemia and lymphoma in the UK and Germany. One disadvantage of these types of immunotoxin for clinical use is their relatively narrow therapeutic window
Therapeutic window
The Therapeutic window of a drug is the range of drug dosages which can treat disease effectively while staying within the safety range. In other words, it is the dosages of a medication between the amount that gives an effect and the amount that gives more adverse effects than desired effects...
and associated potentially life threatening toxicities at dose levels that are therapeutic. During the past 15 years the research group of Dr David Flavell
David Flavell
Dr David J Flavell BSc PhD FRCPath is a British academic research scientist specialising in the development of antibody-based treatments for adults and children with various forms of leukaemia and lymphoma....
at Southampton General Hospital in the UK have been investigating various ways of improving the potency and widening the therapeutic window for saporin-based immunotoxins thereby opening up new possibilities for this class of drug. Most recently saponins (not to be confused with saporin) from Gypsophila paniculata have been show to significantly augment saporin-based immunotoxins directed against human cancer cells by several orders of magnitude.
In the last 15 years, in research begun by R.G. Wiley of Vanderbilt University
Vanderbilt University
Vanderbilt University is a private research university located in Nashville, Tennessee, United States. Founded in 1873, the university is named for shipping and rail magnate "Commodore" Cornelius Vanderbilt, who provided Vanderbilt its initial $1 million endowment despite having never been to the...
, saporin has been used mainly to target specific neuronal populations in lab animals
Animal testing
Animal testing, also known as animal experimentation, animal research, and in vivo testing, is the use of non-human animals in experiments. Worldwide it is estimated that the number of vertebrate animals—from zebrafish to non-human primates—ranges from the tens of millions to more than 100 million...
and eliminate them. This allows the researcher to observe the behavioral changes and associate them with the neuronal populations that were eliminated. For instance, the elimination of the cholinergic neurons of the rat basal forebrain by the toxin created by attaching saporin to an antibody that attaches to, and then internalizes into, only these neurons has created a mimic for the crucial result of Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
in humans (Wenk, Stoehr et al. 1994). In this way, collateral results of the progression of the disease or drugs for the intervention can be studied. More than 300 scientific articles have been published utilizing saporin for study of the nervous systems, and more than 15 specific toxins have been created.
Saporin’s success is probably due to its stability. Santanche et al. have evaluated the physical characteristics of the protein and conclude “(t)he remarkable resistance of saporin to denaturation
Denaturation (biochemistry)
Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent , or heat...
and proteolysis
Proteolysis
Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion.-Purposes:Proteolysis is used by the cell for several purposes...
suggests this protein as an ideal candidate for biotechnological applications” (Santache, Bellelli et al. 1997).