PhD ceremony Mr. G.C. Crismaru: Discovery and properties of enzymes for biocatalytic production of β-amino acids

PhD ceremony: Mr. G.C. Crismaru

Dissertation: Discovery and properties of enzymes for biocatalytic production of β-amino acids

Promotor(s): prof. D.B. Janssen, prof. B.W. Dijkstra

Faculty: Mathematics and Natural Sciences

In nature, non-proteinogenic β-amino acids occur as free compounds such as osmoregulators and signaling molecules or as building blocks in various secondary metabolites such as β-lactam antibiotics or anticancer agents, like taxol.

Preparation of β-amino acids can be achieved in a chemical or enzymatic manner. In his research, Ciprian Crismaru focuses on the enzymatic synthesis, which has significant advantages over the chemical processes such as high enantioselectivity, high regioselectivity, mild reaction conditions and low amounts of catalyst used. Thus, enzyme reactions may provide environmental and economical benefits.

An elegant way to search for enzymes that convert β-amino acids is to perform enrichment experiments. Crismaru describes in his thesis the isolation of 18 bacterial strains that degrade β-alanine, β-glutamate, β-asparagine, β-leucine, β-phenylalanine, D-aspartic acid and β-tyrosine and the search for new deamination enzymes in some of these cultures.

The enzymatic activity associated to β-phenylalanine degradation was an aminotransferase (VpAT). The gene encoding VpAT was cloned and the enzyme was biochemically characterized with respect to substrate scope, reaction mechanism and crystal structure. Another β-phenylalanine aminotransferase homologue (MesAT) was investigated for comparative mechanistic and structural studies. In contrast, a totally different deamination mechanism was observed for β-valine. A lyase-based deamination route is proposed and a genetic analysis of the suspected β-valine pathway is presented. A novel type of lyase, acting on the CoA-conjugate of β-valine and related to enoyl-CoA hydratases, is proposed to catalyze the deamination reaction.

These findings should contribute to the development of a toolbox for the biocatalytic production of β-amino acids.