Zinc is one of the most common transition metal ions in biological systems. As you can expect, it is found as Zn(II) and acts as a strong Lewis Acid providing strong binding interactions. It can be found in several proteins and I can list at least two of them without looking at any textbook: carbonic anhydrase and alcohol dehydrogenase. I can add the zinc fingers too. But, they are not proteins although they can be found in several proteins.
Actually 6 months ago, I made an animation on PyMOL about carbonic anhydrase II and here it is:
I tried to link my youtube video, but it didn't work. Instead I uploaded the original file. Hope that works.
Today I am reading a great review on zinc metalloenzymes and to be honest I haven't finished reading yet. But, it will be over by midnight. I hope you enjoy it.