The present invention provides methods of designing and generating glycerol dehydrogenase (GlyDH) variants that have altered function as compared to a parent polypeptide. The present invention further provides nucleic acids encoding GlyDH polypeptide variants having altered function as compared to the parent polypeptide. Host cells comprising polynucleotides encoding GlyDH variants and methods of producing lactic acids are also provided in various aspects of the invention.
 This invention was made with government support awarded by Department of Energy (DE-FG36-04GO14019 and DE-FG36-08GO88142) and U.S. Department of Agriculture, National Institute of Food and Agriculture (2011-10006-30358). The government has certain rights in the invention.