How do I set a shortcut to screenshot a selected area?

In gnome's screen shot program, the quick keys PrtScn captures the entire screen and alt+PrtScn captures the active window. Is there a way to script or set up the third capture option of a selected area?

Update: I don't seem to have this key already mapped...

1. Open System Settings -> Keyboard -> Shortcuts
2. Select Custom Shortcuts(you can go to Screenshot-s too and it will work)
3. Click +
4. Fill fields
   • Name to Take a screenshot of area
   • Command to gnome-screenshot -a or shutter -s(if u prefer shutter)
5. Click OK
6. Double-click on what you make and set shortcut Shift+PrtSc

— And that's all ... ;)

That shortcut is already built-in: Shift+PrtScr :)

The full-list of screenshot keyboard shortcuts is: