Chloride to the rescue.

On the fiftieth anniversary of the discovery of the Ser-His-Asp catalytic triad, perhaps the most unusual variation on the textbook classic is described: An incomplete catalytic triad in a hydrolase is rescued by a chloride ion (Fig. 1). Structural and functional data provide compelling evidence that the active site of a phospholipase from employs the anion in place of the commonly observed Asp, reminding us that even well-trodden scientific ground has surprises in store.