Abstract
ABSTRACTThe postsynaptic density (PSD) is a functionally active zone involved in excitatory synaptic transmission in mammalian central nerve system. Inductively Coupled Plasma-Mass (ICP-MASS) analyses reveal that the isolated PSD proteins contain zinc at a concentration of 4.1 nmol/mg. A treatment of 8M urea leads to the dissociation of the PSDs into small components and depletion of most of the zinc ions bound to the PSD. Removing urea by dialysis, dissociated PSD proteins do not reassemble into aggregates by themselves.We also find that the majority of the 8M urea treated and dialyzed PSD proteins are bound to a Zn-Nitrilotriacetic acid (Zn-NTA) column. We then elute the column with different reagents (Tris-HCl, urea, imidazole, guanidine hydrochloride, SDS, glycerol, or Triton). After removing urea by dialysis, the PSD proteins eluted from Zn-NTA column with urea can form aggregates in the presence of zinc ions. The mixtures containing the PSD proteins eluted with urea and other reagents from a Zn-NTA column can also form aggregates with different degrees of compactness. Morphological studies indicate that the resultant zinc-induced aggregates are not identical to the original PSD. Our results suggest that the zinc ions bound to certain zinc binding proteins be eluted with urea from Zn-NTA column. The zinc binding proteins may play important roles in the formation and maintenance of the structure of the PSD.