In Mint Mate 17.3, this still needs to be configured from a fresh install. It's easily doable by going to
Menu -> Preferences -> Keyboard Shortcuts and adding a new
Custom Shortcut to the preferred file manager.
Doing this binds the shortcut to Mod4 + E. Unfortunately, if no other changes are made, this will not work when using the left Super key, only when using the one on the right side of the keyboard.
When you press the left Super key, regardless of any custom shortcuts, the menu will appear and the second keystroke will be ignored. This is because the Mate menu is bound to Super_L, not Mod4.
The only solution I've found is to change the key assigned to opening the Mate menu: Ctrl + Super_L for instance.
This setting can be changed by right clicking
Menu, going to
Preferences, then changing the shortcut on the
Main button tab.
It's not a very elegant solution, but it does allow the file manager to be launched with Super + E using the Super key on the left side of the keyboard.