Mark D. Bednarski - US grants

Recent spectacular advances in biotechnology--site directed mutagenesis, monoclonal antibodies, semi-synthetic enzymes, membrane reactors and others--are rapidly providing new and powerful forms of catalysis. Our research group is investigating how to integrate this new technology with classical organic chemistry to synthesize materials for biology and medicine. Specific goals are: 1) to develop readily available proteins as catalysts for use in natural product synthesis 2) to engineer new proteins through the use of mutagenesis; 3) to develop proteins for synthetic transformations that are difficult or impossible to perform using classical organic chemistry. Natural products serve as a goal to develop new synthetic methodology. We are pursuing the stereoselective synthesis of unusual peptides such as statine, the construction of antitumor agents (adriamycin and daunorubicin), the synthesis of glycosidase inhibitors (castanospermine and norjirimyucin) and the synthesis of noel alkaloids (gephrotoxin) to develop the use of enzyumes in organic synthesis. To effectively use enzymes for synthetic chemistry, methods are also being developed to use proteins in organic solvents and alter their substrated specificity either through chemical or genetic techniques. We are pursuing both approaches. Our group, for example, is using mutagenesis to change the substrate specificity of carbon-carbon bond forming enzymes. Mutations are made on DNA which codes for an aldolase protein and the altered gene spliced into a plasmid which is transformed into E. coli. These mutants are forced to accept unnatural (synthetic) substrates by coupling the occurence of the desired catalytic process with the release of material which is necessary for the survival of the organism. All relevant enzymes are designed for synthetic applications, that is to stereoselectively form key bonds in the construction of natural products. The development of methods in biotechnology to execute stereoselective organic transformations is important for the development of new safe and economical methods in organic chemistry.

This collaborative project between workers at Berkeley and UCSF is designed to produce new polymeric peptides with useful properties. The investigators are all excellent scientists, although all well supported by other grants. In particular Dr. Craik has another NSF grant which duplicates his effort in this proposal. The P.I. has developed enzymatic methods for reacting amino acid esters in organic solvents with free amino acids to generate dipeptides. The approach has been extended to a tetra peptide, but the strategy seems unlikely to produce useful polymers, although it might be practical for short peptides. It should be noted that carboxypeptidase cannot be employed in such syntheses because it does not have and acyl enzyme intermediate. There are some interesting ideas in this proposal, but the practicality of synthesizing polypeptides by these approaches seems minimal.