You can assign a custom keyboard shortcut
Got to Settings -> Keyboard -> Custom Shortcuts
Click on + sign to add a new custom shortcut. Give the command as “gnome-screenshot” (attached image)
after clicking on Add button, you can see the newly added shortcut in the list. Click on the right end of that row which labeled ‘Disabled’. It will change to ‘New Accelerator’. Then press the Print Screen or Print button on keyboard. Thats it…
Now you can take screenshot by simply pressing Print button….
Also refer the attached Screenshot posted by Chris Druif (in G+) for more options available for screenshots