The design of enzymes with new functions and properties has long been a goal in protein engineering. Here, we report a strategy to change the catalytic activity of an existing protein scaffold. This was achieved by simultaneous incorporation and adjustment of functional elements through insertion, deletion, and substitution of several active site loops, followed by point mutations to fine-tune the activity. Using this approach, we were able to introduce beta-lactamase activity into the alpha beta/beta alpha metallohydrolase scaffold of glyoxalase II. The resulting enzyme, evMBL8 (evolved metallo beta-lactamase 8), completely lost its original activity and, instead, catalyzed the hydrolysis of cefotaxime with a (k(cat)/K-m)(app) of 1.8 x 10(2) (mole/titer)(-1) second(-1), thus increasing resistance to Escherichia coli growth on cefotaxime by a factor of about 100.