Practice question

Gram negative envelope integrity depends on covalent linkage between outer membrane and peptidoglycan preventing blebbing and leakage. Braun's lipoprotein Lpp 58 amino acid mature after signal peptidase II lipid modification N acyl S diacylglycerol cysteine anchoring into inner leaflet outer membrane plus third acyl chain, most abundant protein about seven times ten to five copies per cell. C terminal lysine forms peptide bond to meso diaminopimelic acid of peptidoglycan tetrapeptide via LD transpeptidases LdtA B C catalyzing attachment post export. Two thirds of Lpp exist bound form linking layers, one third free form. Periplasmic distance regulated by Lpp length; mutants lengthening Lpp increase periplasm width affecting division. Lpp interacts with OmpA noncovalently stabilizing envelope. Disruption causes hypersensitivity to detergents hydrophobic antibiotics, increased outer membrane vesicle release, activated sigma E stress response. Therefore Braun's lipoprotein serves to attach outer membrane to peptidoglycan acting molecular staple maintaining envelope mechanical coupling, not as enzyme synthesizing peptidoglycan, facilitating folding, or directly blocking antibiotic entry though indirectly supports barrier function.