I'm working with emacs (on the terminal) and I use screen to switch between terminals. The key combination Ctrl+A is grabbed by screen. Is there a way to change screen key binding?
Sure, you can change the binding in either Screen or Emacs.
I use Ctrl+\ in Screen, which is used by very few applications. It's used in the terminal to send the QUIT signal — a stronger version of Ctrl+C, which fewer applications catch and may produce a core dump. That's rarely useful, and if you need it you can press Ctrl+\ \. A bigger argument against Ctrl+\ is that it's hard to type on some keyboard layouts. Anyway, pick the key you prefer.
To change the Screen escape key, use the
Then use Ctrl-Z instead of Ctrl-A to control screen.