Do you have just one key?? If so, I'd get a another key.

The driver's door look key barrel and lock assembly is not very sturdy...Time and again when E53 owners start using the key in the door to manually lock/unlock the door, the barrel assembly breaks. You don't want that.

Any BMW key of a similar vintage will synch to lock/unlock your car. To see if you your key is a problem, find a used key or borrow one and see if you can synch it with your car's locking systems. Obviously a used key won't start your car.

Some people use one key to start the car and another used key to lock/unlock...if you do this, you need to figure out how to charge the used key.