PhD ceremony: Mr. G. Fibriansah, 12.45 uur, Academiegebouw, Broerstraat 5, Groningen
Dissertation: Structure and mechanism of action of two bacterial enzymes: MltE from Escherichia coli and AspB from Bacillus sp YM55-1
Promotor(s): prof. B.W. Dijkstra
Faculty: Mathematics and Natural Sciences
In this thesis, crystal structures and reaction mechanisms of two different bacterial enzymes are described. The first enzyme is the lytic transglycosylase MltE from Escherichia coli, which cleaves the b-1,4-glycosidic bonds between N-acetylmuramic acid and N-acetylglucosamine residues in the bacterial cell wall material peptidoglycan. The enzyme is thought to function in bacterial cell wall turn-over, remodeling and maintenance, which makes it a potential target for antibacterials. MltE is distinct because it is one of the few endo-acting lytic transglycosylases of E. coli. The crystal structures of MltE in a substrate-free state, in a binary complex with chitopentaose, and in a ternary complex with the glycopeptide inhibitor bulgecin A and a murodipeptide allowed a detailed analysis of the saccharide-binding interactions. In combination with site-directed mutagenesis studies the structures explain why MltE is an endo-acting enzyme and how it catalyzes the reaction. The second enzyme is the aspartase AspB from Bacillus sp. YM55-1, which catalyzes the reversible deamination of L-aspartate into fumarate and ammonia. Aspartases are used as biocatalysts for the industrial production of enantiopure L-aspartate, an important starting compound for the synthesis of food additives and artificial sweeteners. However, their precise catalytic mechanism has remained elusive because of lack of information on the binding mode of substrate, product or substrate analogs. Crystal structures of AspB in an unliganded state and with bound L-aspartate have now revealed the residues responsible for catalysis. Accompanying site directed mutagenesis and enzyme kinetics experiments allowed to fully explain the mechanism of action of this enzyme.
Prof. Roelfes receives NWO ENW-KLEIN grant of EUR 304.000
for his project ‘Time-resolved dynamics of glutamate transporters'
The core business of Dutch universities is to prepare students for their future: a career in our open, internationally oriented society and knowledge economy. To this end, all Dutch universities have an international perspective firmly entrenched in...