A common result of scorpion stings, pancreatitis is an inflammation of the pancreas. ECU microbiologist Dr. Paul Fletcher believed that scorpion venom might be used as a way to discover how pancreatitis occurs – to see which cellular processes are affected at the onset of the disease. Fletcher pinpointed a protein production system found in the pancreas that seemed to be targeted by the venom of the Brazilian scorpion Tityus serrulatus and then contacted NC State physicist Dr. Keith Weninger, who had studied that particular protein system.
“This particular protein system has special emphasis at two places in the body – the pancreas and the nervous system,” Weninger says. “In the pancreas, it is involved in the release of proteins through the membrane of a cell.” The pancreas specializes in releasing two kinds of proteins using separate cells: digestive enzymes that go into the small intestine and insulin and its relatives that go into the bloodstream, yet this same release mechanism is important in all of our cells for many processes.
Cells move components in and out through a process called vesicle fusion. The vesicle is a tiny, bubble-like chamber inside the cell that contains the substance to be moved, stored and released – in this case, proteins like enzymes or hormones. The vesicle is moved through the cell and attaches to the exterior membrane, where the vesicle acts like an airlock in a spaceship, allowing the cell membrane to open and release the proteins without disturbing the rest of the cell’s contents. The proteins that aid in this process are known as Vesicle Associated Membrane Proteins, or VAMPs.
Weninger provided Fletcher with two different VAMP proteins found in the pancreas, VAMP2 and VAMP8. They were engineered to remove the membrane attachments so they could be more easily used for experiments outside cells and tissues. Fletcher’s team demonstrated that the scorpion venom attacked the VAMP proteins, cutting them in one place and eliminating the vesicle’s ability to transport its protein cargo out of the cell.
The results were published in the March 5 issue of the Journal of Biological Chemistry.
“We found that a particular enzyme in the scorpion’s venom removes a peptide, or small protein, that allows the vesicle to fuse with the cell membrane,” Fletcher says. “If you remove a pancreatic cell’s ability to absorb or release components, you end up with pancreatitis.”
“Viruses often exploit the same mechanism of vesicle fusion, but in reverse, in order to invade cells and replicate,” Weninger adds. “This work furthers our understanding of a basic cellular process and may lead to treatments for viruses and advances in treatments like chemotherapy, by allowing targeted drug delivery only to cancer cells.”
The Department of Physics is part of NC State University’s College of Physical and Mathematical Sciences.
Note to editors: An abstract of the paper follows.
“Vesicle-associated Membrane Protein (VAMP) Cleavage by a New Metalloprotease from the Brazilian Scorpion Tityus serrulatus*”
Authors: Paul L. Fletcher, Jr., Maryann D. Fletcher, East Carolina University; Keith Weninger, Trevor E. Anderson, North Carolina State University; and Brian M. Martin, National Institutes of Health
Published: March 5, 2010, in Journal of Biological Chemistry; VOL. 285, NO. 10, pp. 7405–7416
Abstract: We present evidence that venom from the Brazilian scorpion Tityus serrulatus and a purified fraction selectively cleave essential SNARE proteins within exocrine pancreatic tissue. Western blotting for vesicle-associated membrane protein type v-SNARE proteins (or synaptobrevins) reveals characteristic alterations to venom-treated excised pancreatic lobules in vitro. Immunocytochemistry by electron microscopy confirms both the SNARE identity as VAMP2 and the proteolysis of VAMP2 as a marked decrease in secondary antibody-conjugated colloidal gold particles that are predominantly associated with mature zymogen granules. Studies with recombinant SNARE proteins were used to determine the specific cleavage site in VAMP2 and the susceptibility of VAMP8 (endobrevin). The VAMP2 cleavage site is between the transmembrane anchor and the SNARE motif that assembles into the ternary SNARE complex. Inclusion of divalent chelating agents (EDTA) with fraction v, an otherwise active purified component from venom, eliminates SNARE proteolysis, suggesting the active protein is a metalloprotease. The unique cleavages of VAMP2 and VAMP8 may be linked to pancreatitis that develops following scorpion envenomation as both of these v-SNARE proteins are associated with zymogen granule membranes in pancreatic acinar cells. We have isolated antarease, a metalloprotease from fraction v that cleaves VAMP2, and report its amino acid sequence.