Regulation of the synaptic trafficking of the vesicular glutamate transporter VGLUT1.

Three vesicular glutamate transporters (VGLUT1, -2, and -3) are found in the mammalian central nervous system. The transporters are expressed in different brain regions in synapses with different release properties. Recent work has suggested that the most widely expressed isoforms, VGLUT1 and -2, determine some of the functional properties of their synapses. While the three transporters have very similar transport activity, their synaptic trafficking appears to be differentially regulated and these trafficking differences may account for the observed functional differences. The main focus of my work has been to identify two additional dileucine-like endocytic motifs in the VGLUT1 N-terminus that can mediate trafficking of the transporter and which are not well-conserved in VGLUT2 or -3. These motifs are in addition to a C-terminal dileucine-like motif that is conserved between the three isoforms. My work also demonstrates that the different dileucine-like motifs utilize different clathrin adaptor proteins with the C-terminal motif using AP-2 and the N-terminal motifs using AP-1. Finally, comparison of VGLUT1 and VGLUT2 demonstrates that VGLUT2 is far more dependent on the conserved C-terminal motif for proper synaptic targeting.Another line of my research was the identification of novel protein interactors with the two polyproline motifs that are uniquely found in the C-terminus of VGLUT1, downstream of the conserved dileucine-like motif. In vitro binding assays identified several intriguing candidates. However, further work is required to determine if these interactions occur in vivo and, if so, how they modulate VGLUT1 function. A final line of research examined whether other putative motifs in the C-terminus of VGLUT1 regulate trafficking of the transporter. While some interesting effects were observed, the functional significance of these motifs remains to be determined