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Function
Ectatomin is the protein that causes the toxic effect of the venom. Ecataomin targets the cell membrane, creating pores that cause ion leakage and low membrane resistance. The pores created is due to the ectatomin channel forming ability. These channel/pores are formed selectively on the membrane, they occur at positive cis-potential locations. At these locations two ectatomin molecules must be present in order for the formation of a pore. The protein is able to insert itself into the membrane and interact with the protein kinases part of the signaling cascade. Though when raised to a higher concentration, the protein instead inhibits the autophosphorylation of pp60c-src protein tyrosine kinase. At this lower concentration ectatomin is able to enter the membrane but is not able to penetrate inside the cell. At higher concentrations which are required for hemolytic and cytolytic effects to occur the toxin acts more like a detergent similar to mellitin. Ectatomin causes the inhibition of the calcium channels. The toxin protein binds to the gated channel when it has changed two its mode 2. This mode is occurs when B-adrengeric stimulates the channel. The toxin can bind to mode 1 channels but seems to have a higher affinity for the channel after the B-adrengeric stimulation has occurred.
Relevance
Ectatomin belongs to the ectatomin family of toxins. It is specifically the ectatomin-ET subfamily.
Ectatomin is comes from the Ectatomma tuberculatum ant. This ant is located in upper south America region and the connecting lower north America region. This ant is one of the 15 species that make up the Ectatomma species. This ant normally builds nests on the ground around trees. These ants are built up around two type’s ether they are workers or there is a queen. The part of the body where the toxin originates is the venom gland. This gland is connected to a stinger which allows the ant to stab its prey and deliver the toxin. Though the main purpose of the toxin is to kill the prey or attacker, there seem to be other roles that can be used for. Ectatomin is the main protein used for toxic effects but of course the toxin is filled with other proteins. The venom can be used for colony asepsis, preventing infections in food and other ants. The toxin even has paralysis effects caused by the arginine kinase, this can allow the ants to move their still alive prey to the colony.
These were able to determine the protein structure and while using MARDIGRAS program it was also able to creating accurate distance constraints for protein to protein measurements. The DIANA program was used to find the disulfide bridges. CHARMm prgrom was used to touch up and refine the protein structure. Using these programs the rms deivation was .75A for the heay backbone atoms, for overall heavy atoms it was 1.25 A
Structural highlights
Ectatomin is a simple toxin, with a molecular weight of 7928 Da, pl 9.95) The protein is made up of two polypeptide chains, these chains are homologous and amphiphilic. The A chain is 37 amino acids and the B chain is 34 amino acid in length. The two chains are held together by a disulfide bond. The chains are made from antiparallel alpha helices, these two alpha helices are connected by a hinge made up form a disulfide bridge and four amino acids. This hinger region creates additional stability by forming a hairpin unit and helps the disulife bonds stay stable.The PTMs that occur on this protein are disulfide bonds. These bonds connect the 12-34 sites of the A subunit. Also connect the 22 of subunit A to the 20 site of sub unit B. There is a final disulfide bond that connects the 10 site to the 32 site of subunit B. These are the bonds that hold the protein in the bundle shape that you see in the diagram.
