Purification and functional characterization of phiX174 lysis protein E

Area of Science:

• Bacteriology and Virology
• Molecular Biology
• Biochemistry

Background:

• Bacteriophages employ "protein antibiotics" to lyse host cells by inhibiting cell wall biosynthesis.
• The bacteriophage protein E is a known inhibitor of MraY, an essential enzyme in bacterial murein precursor synthesis.

Purpose of the Study:

• To purify the bacteriophage protein E, which has been challenging due to its lethality.
• To elucidate the inhibitory mechanism of protein E on the MraY enzyme.
• To reconcile conflicting previous findings regarding E's inhibition of membrane-embedded versus solubilized MraY.

Main Methods:

• Purification of bacteriophage protein E from Escherichia coli.
• Enzyme inhibition assays using a fluorescently labeled substrate analogue to study MraY activity.
• Analysis of MraY mutant proteins selected for resistance to protein E, correlating in vitro and in vivo data.

Main Results:

• Protein E was successfully purified, overcoming previous overexpression challenges.
• Protein E acts as a noncompetitive inhibitor of detergent-solubilized MraY against both substrate and lipid components.
• Mutations conferring E resistance in MraY correlate with enzyme affinities, supporting a conformational inactivation model.

Conclusions:

• Protein E directly inhibits MraY activity, likely through binding to a transmembrane domain.
• This binding induces a conformational change, inactivating MraY and disrupting bacterial cell wall synthesis.
• The findings propose a revised model for E-mediated MraY inhibition, distinct from previous complex-formation hypotheses.