An overbet often represents a polarized range, meaning either a bluff or an extremely strong hand but generally not something in between like JT or QT. That turns your AT into a bluff-catcher, meaning that you can't expect him to bet a hand you're ahead of for value. That by itself doesnt' tell you whether to call or fold, but hopefully it helps you to start thinking about his range.

Based on the flop and turn action, what do you think is his range for getting to the river. In other words, ignore the shove for the moment and first think about what his range is just for seeing the river. Let me know your thoughts on that and we'll go from there.