title: Zinc-mediated dimerization and its effect on activity and conformation of staphylococcal enterotoxin type C.
abstract: Staphylococcal enterotoxins are superantigen exotoxins that mediate food poisoning and toxic shock syndrome in humans. Despite their structural and functional similarities, superantigens display subtle differences in biological properties and modes of receptor binding as a result of zinc atoms bound differently in their crystal structures. For example, the crystal structures of the staphylococcal enterotoxins in the type C serogroup (SECs) contain a zinc atom coordinated by one aspartate and two histidine residues from one molecule and another aspartate residue from the next molecule, thus forming a dimer. This type of zinc ligation and zinc-mediated dimerization occurs in several SECs, but not in most other staphylococcal enterotoxin serogroups. This prompted us to investigate the potential importance of zinc in SEC-mediated pathogenesis. Site-directed mutagenesis was used to replace SEC zinc binding ligands with alanine. SEC mutants unable to bind zinc did not have major conformational alterations although they failed to form dimers. Zinc binding was not essential for T cell stimulation, emesis, or lethality although in general the mutants were less pyrogenic. Thus the zinc atom in SECs might represent a non-functional heavy atom in an exotoxin group that has diverged from related bacterial toxins containing crucial zinc atoms.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA. young-in.chi@joslin.harvard.edu
authors.forename: Young-In
authors.initials: YI
authors.lastname: Chi
authors.forename: Ingrid
authors.initials: I
authors.lastname: Sadler
authors.forename: Lynn M
authors.initials: LM
authors.lastname: Jablonski
authors.forename: Scott D
authors.initials: SD
authors.lastname: Callantine
authors.forename: Claudia F
authors.initials: CF
authors.lastname: Deobald
authors.forename: Cynthia V
authors.initials: CV
authors.lastname: Stauffacher
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Bohach
mesh_terms: D000818:Animals; D001665:Binding Sites; D002455:Cell Division; D002850:Chromatography, Gel; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004768:Enterotoxins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011817:Rabbits; D013601:T-Lymphocytes / Q000378:metabolism; D013997:Time Factors; D014357:Trypsin / Q000494:pharmacology; D033921:Vesicular Transport Proteins; D015032:Zinc / Q000737:chemistry / Q000378:metabolism*
chemical_list: D004768:Enterotoxins; D008024:Ligands; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D033921:Vesicular Transport Proteins; C034959:enterotoxin C, staphylococcal; D014357:Trypsin; D015032:Zinc