Rashek Kazi

1st Year Medical Student

Department: School of Medicine

Graduate Program: TBD

Advisor: TBD

Abstract (rotation):

Advisor: Dr. Lonnie Wollmuth, Dept. of Neurobiology and Behavior, SBU

Title:  Transmembrane interactions are necessary for glutamate receptor function

Glutamate receptors (GluRs) are the primary excitatory ligand gated ion channel in the mammalian central nervous system. There are several classes of GluRs including NMDA, AMPA, and kainate receptors. These receptors all contain an extracellular amino terminal domain (ATD), 3 transmembrane domains (M1, M3, & M4), a pore loop (M2), a ligand binding domain (LBD), and an intracellular carboxy terminal domain (CTD). Of the membrane spanning domains, the function of the M4 segment (located proximal to the CTD and distal to the LBD)--which is unique to eukaryotic GluRs-- has come under recent scrutiny. We found that AMPA receptors (AMPARs) in which the M4 domain was removed showed a complete loss of function even though this topologically resembled the functional prokaryotic GluR0 subunit. Furthermore, immunochemistry studies showed that truncated AMPARs translocated to the membrane suggesting that the importance of the domain lay in it's interaction with other transmembrane segments or with the ligand binding domain. To test the potential interaction of M4 with the LBD, mutants which contained glycine residues in the LBD-M4 linker region were constructed. We found that insertions of up to 8 glycines had no effect on glutamate receptor function suggesting that there is no interaction between M4 and the LBD. To test the potential relationship with other transmembrane domains, tryptophan substitution mutants in the M4 domain were constructed. These mutants showed a cyclical increase and decrease in glutamate-activated whole cell currents which suggests an alpha-helical face on M4 that interacts with one of the other transmembrane domains. These experiments suggest that the interaction of the M4 segment with other transmembrane segments rather than the LBD is necessary for receptor function.