The N-terminal FMDE motif of Stx3 is required for axonal targeting.

<p>(A) Stx3 wild-type and mutant constructs are schematically depicted. Tandem myc epitope tags are present at the C-terminus (extracellular domain) to facilitate surface labeling [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0163671#pone.0163671.ref023" target="_blank">23</a>]. Stx3Δ38 contains a 38 amino acid N-terminal truncation. In Stx3_AAA, three residues of the <u>F</u>M<u>DE</u> motif of Stx3 were changed to alanine as indicated by ‘AAA’. (B) Mutant Stx3 constructs lacking the FMDE motif are mistargeted to the somatodendritic, as well as axonal plasma membrane. Neurons were coinfected with adenoviruses expressing Stx3Δ38 or Stx3_AAA and GFP, and were live surface labeled with anti-myc antibody (red). Arrowheads denote axon. Bar, 20 μm. (C) Quantification of axon:dendrite polarity index for surface (red bars) and internal (black bars) Stx3, Stx3Δ38 and Stx4 in mature hippocampal neurons. PI ratios for Stx3Δ38 and Stx4 were significantly reduced compared to Stx3. Error bars, SEM; N = 14–18; * P < 0.0001.