New grads can get 50k in Berlin. You'd be an idiot to move there for less than 60-70k these days. I'm constantly hit up by recruiters who're trying to lure me back for 80-90k.
If single, you will have a blast in Berlin with 45k. If you're moving with a dependent, that's a bit tight (as a newcomer, you will never find the best deals regarding accommodation, there's a fair supply of newly built apartments in Berlin, but they aren't cheap).
45k/year is enough for a single person or even a couple living more frugal.