And once it positions into this location, the lone pair of electrons on the nitrogen of this side chain of the histidine basically interact with this age and they deprotonate that water molecule. Now, this is a very important step because just like serine contains the alcohol and the alcohol is not a strong enough nuclear file. So what happens is the H atom is removed to create alcoxide and transform into a good nucleophile. In this case, water is also not a strong enough nucleophile to actually attack the carbon of this double bond. And so what must take place is again, we see that the histidine actually takes away the H from this oxygen and that transforms the water into a hydroxyl. And the hydroxide is a good enough nucleophile.