Complex formation between Mur enzymes from Streptococcus pneumoniae

Peptidoglycan is one of the major components of the bacterial cell wall, being responsible for shape and stability. Due to its essential nature, its biosynthetic pathway is the target for major antibiotics, and proteins involved in its biosynthesis continue to be targeted for inhibitor studies. The biosynthesis of its major building block, Lipid II, is initiated in the bacterial cytoplasm with the sequential reactions catalyzed by Mur enzymes, which have been suggested to form a multi-protein complex in order to facilitate shuttling of the building blocks towards the inner membrane. In this work, we purified MurC, MurD, MurE, MurF and MurG from the human pathogen Streptococcus pneumoniae and characterized their interactions using chemical cross-linking, mass spectrometry, analytical ultracentrifugation, and microscale thermophoresis. Mur enzymes interact strongly as binary complexes, with interaction regions mapping mostly to loop regions. Interestingly, MurC, MurD and MurE display ten times higher affini...