ZHAO, Huimin

Department of Chemical Engineering

Ph.D. (1998) California Institute of Technology

   Research Topics

     - Biocatalysis

     - Directed Enzyme Evolution

     - Directed Pathway Evolution

   Research Interests

   Molecular Bioengineering, Biotechnology   Research in my group focuses on the development and applications of directed evolution technologies to engineering new proteins/enzymes, pathways and genomes. Directed evolution mimics the Darwinian evolutionary processes, mutation/recombination and screening/selection in the test tube, allowing for rapid and direct isolation of biomolecules based on their functional properties. The goal of my research is to develop genetically based bioproducts/ bioprocesses for pharmaceutical, agricultural and industrial chemical applications and to understand their biochemical and biophysical mechanisms at the molecular level. A survey of recent topics of interest is given below.

    (1)Directed Evolution of Enzymes. We are applying directed evolution methods to engineering several practically important enzymes. For example, one project is to engineer novel substrate specificity of a hydrolytic haloalkane dehalogenase. This enzyme can be potentially used as a bioremediation agent in detoxification of aliphatic halogenated hydrocarbons and as a biocatalyst in the synthesis of chemical compounds such as epichlorohydrin. But its application is limited by its narrow substrate specificity and low activity. Therefore, we will apply a novel targeted combinatiorial mutagenesis method to randomly mutagenize the active site of this enzyme and isolate the variants with increased activity toward the substrate of interest. Another project is to increase the biological activity of antifreeze proteins. We will use DNA shuffling to recombine several antifreeze protein genes isolated from fish, insect and plant followed by selection of variants with increased activity. The evolved antifreeze proteins could be used in low temperature preservation of gametes and embryos of domestic animals and in the creation of cold/frost resistant transgenic plants.

   (2) Directed Evolution of Pathways Biosynthetic pathways, have been widely used in production of natural products. Natural products, isolated from microorganisms and plants, make up as much as 40% of the drugs in current use. Stimulated by the discovery of antibacterial agents like penicillin, cephalosporin and streptomycin during 1930s and 1940s, the pharmaceutical industry has spent considerable resources to discover new biologically active natural products. However, the rate of discovering new drugs or improved ones has diminished with time. An effective means to increase this rate is the genetic manipulation of the existing biosynthetic pathways by directed evolution technologies. Examples of biosynthetic pathways of interest include B-lactam pathway and alkanoid pathway. Currently, we are developing new experimental methods for efficient generation of molecular diversity of the products.

   Key Word Directed Evolution, DNA Shuffling, Biosynthetic, Pathways, Biocatalysis