Date of Award

Spring 2012

Document Type

Thesis

Degree Name

Bachelor of Science

Department

Biochemistry & Molecular Biol.

First Advisor

Dr. Lisa Gentile

Abstract

Implicit in cellular mechanisms essential for learning and memory, NMDA receptors are heterotetrameric members of the family of ionotropic glutamate receptors. Activation of the glutamate-specific receptor subunits results in the opening of ion channels, triggering an excitatory pathway, which can be moderated by certain endogenous and exogenous compounds. Previous research with the endogenous neurosteroids pregnenolone sulfate (PS) and 3α-hydroxy-5-β-20-one sulfate (PregS) have indicated that the binding of these neurosteroids to NMDA receptors containing the four A-D isoforms of the GluN2 subunit affects current flow through them1. Binding of PS to NMDA receptors containing GluN2A or GluN2B subunits causes an increased amount of current flow through the channel, whereas binding of PS to receptors containing GluN2C and 2D subunits decreases current flow through these channels. Binding of PregS to any NMDA receptor also decreases current flow. Binding studies from our lab have determined that the neurosteroids PS and PregS bind to the amino terminal domain (ATD) of both GluN2B and GluN2D subunits. The ATD segment used in these studies consisted of residues 121-292. Binding of both neurosteroids was monitored between pH 6.0 and 8.0. Results demonstrated that the binding of PS to GluN2B and D ATDs occurred only between pH 6 and 6.5. PregS showed similar pH dependence for the GluN2B ATD, although binding was restored at pH 8. The pH dependence of neurosteroid binding suggests the importance of a protonated histidine residue in each binding interaction. The GluN2B ATD segment contains one histidine at residue 127, whereas the corresponding GluN2D ATD contains 3 histidines at residues 143, 182, and 202. Results from preliminary structural and neurosteroid binding studies of His to Ala and Gln mutations in the GluN2D ATD are presented.

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