REPOSITORY > RESULTS

Abstract

The bacteria are surrounded by a cell wall that provides them with mechanical protection.
The cell wall consists of a peptidoglycan scaffold, built from polysaccharide strands crosslinked
by peptides. Autolysins are enzymes that remodel the cell wall during growth and
division. Among them are N-acetylglucosaminidases that cleave the glycosidic bonds
between NAG and NAM monosaccharide residues. Here we focused on Nacetylglucosaminidases
of the Staphylococcus aureus, a pathogenic microorganism that
represents a major public health burden.
We have identified four peptidoglycan N-acetylglucosaminidases that are highly
conserved in S. aureus, SagB, AtlA-gl, AtlE and ScaH-gl. Crystal structures have revealed
that the enzymes have a highly similar secondary structure organization and markedly
different tertiary structure. After the analysis and comparison of their substrate binding
sites we proposed that for the enzymatic reaction to proceed, a substantial conformational
change needs to take place. This leads to closing of the enzyme. Molecular dynamics
simulations have confirmed that closed conformations of these enzymes are stable, but only
when the substrate is bound. This indicates that the conformational change occurs with
binding of the substrate.
Study of the catalytic mechanism of AtlE has shown that for of the reaction only one
catalytic amino acid is necessary. As the energetically favorable path, water-assisted
catalysis was established. Additionally, we proposed the transition state of the reaction is
represented by oxocarbenium ion.
In addition, we have designed the first compounds that AtlE binds. Compounds from
the structural class of (phenylureido)piperidinyl benzamides were found to exhibit
promising binding affinity in the micromolar range.
The results we present here are a basis for further drug target validation of S. aureus
N-acetlyglucosaminidases as drug targets.