title: HgEDTA complex inhibits GTP interactions with the E-site of brain beta-tubulin.
abstract: We have found that EDTA and EGTA complexes of Hg2+, which conventional wisdom has assumed are biologically inert, are potentially injurious to the neuronal cytoskeleton. Tubulin, a major protein component of the neuronal cytoskeleton, is the target of multiple toxicants, including many heavy metal ions. Among the mercurials, inorganic mercuric ion (Hg2+) is one of the most potent inhibitors of microtubule polymerization both in vivo and in vitro. In contrast to other heavy metals, the capacity of Hg2+ to inhibit microtubule polymerization or disrupt formed microtubules cannot be prevented by the addition of EDTA and EGTA, both of which bind Hg2+ with very high affinity. To the contrary, the addition of these two chelating agents potentiates Hg2+ inhibition of tubulin polymerization. Results herein show that HgEDTA and HgEGTA inhibit tubulin polymerization by disrupting the interaction of GTP with the E-site of brain beta-tubulin, an obligatory step in the polymerization of tubulin. Both HgEDTA and HgEGTA, but not free Hg2+, prevented binding of [32P]8N3GTP, a photoaffinity nucleotide analog of GTP, to the E-site and displaced bound [32P]8N3GTP at low micromolar concentrations. This complete inhibition of photoinsertion into the E-site occurred in a concentration- and time-dependent fashion and was specific for Hg2+ complexes of EDTA and EGTA, among the chelating agents tested. Given the ubiquity of Hg2+ in the environment and the widespread use of EDTA in foodstuffs and medicine, these mercury complexes may pose a potentially serious threat to human health and play a role in diseases of the neuronal cytoskeleton.
authors.affiliation: Division of Medicinal Chemistry and Pharmaceutics, College of Pharmacy, University of Kentucky Medical Center, Lexington.
authors.forename: E F
authors.initials: EF
authors.lastname: Duhr
authors.forename: J C
authors.initials: JC
authors.lastname: Pendergrass
authors.forename: J T
authors.initials: JT
authors.lastname: Slevin
authors.forename: B E
authors.initials: BE
authors.lastname: Haley
mesh_terms: D000345:Affinity Labels; D000818:Animals; D001386:Azides; D001665:Binding Sites / Q000187:drug effects; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D004492:Edetic Acid / Q000494:pharmacology*; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008628:Mercury / Q000494:pharmacology*; D010761:Phosphorus Radioisotopes; D010777:Photochemistry; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D014404:Tubulin / Q000187:drug effects* / Q000378:metabolism
chemical_list: C021961:8-azidoguanosine triphosphate; D000345:Affinity Labels; D001386:Azides; D010761:Phosphorus Radioisotopes; D014404:Tubulin; D006160:Guanosine Triphosphate; D004492:Edetic Acid; D008628:Mercury; D008274:Magnesium