Abstract
AMPA receptors are one of the ionotropic glutamate receptors in neurons which play an important role in synaptic plasticity. Out of four main subunits of the AMPA receptor, GluA1 and GluA2 heteromers are most abundant in brain. Crystallography and single molecule studies show that GluA1 and GluA2 prefers to assemble in 2:2 stoichiometry while forming an AMPA receptor tetramer. The reason behind this preference is not yet understood. One possibility is that the Q/R editing site in the pore forming loop of GluA2's trans-membrane domain, which renders the subunit calcium impermeable, drives the preference for 2:2 stoichiometry. To test the hypothesis, two different chimera structures GluA1-2-1 and GluA2-1-2 are cloned by swapping the trans-membrane domain (containing the RNA editing site) of either subunit. The assembly of chimeras are observed in Xenopus laevis oocytes by single-molecule microscopy. A subunit counting method based on the bleaching steps of chimeras tagged with fluorescent proteins tagged is used to understand the stoichiometry of the assembled chimeras. Thus it is aimed to decipher the molecular determinants behind the 2:2 stoichiometry preference of AMPA receptor subunits.
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