Core structure of the outer membrane lipoprotein from Escherichia coli at 1.9 A resolution

The outer membrane lipoprotein of the Escherichia coli cell envelope has ch aracteristic lipid modifications at an amino-terminal cysteine and can exis t in a form bound covalently to the peptidoglycan through a carboxyl-termin al lysine. The 56-residue polypeptide moiety of the lipoprotein, designated Lpp-56, folds into a stable, trimeric helical structure in aqueous solutio n. The 1.9 Angstrom resolution crystal structure of Lpp-56 comprises a para llel three-stranded coiled coil including a novel alanine-zipper unit and t wo helix-capping motifs. The amino-terminal motif forms a hydrogen-bonding network anchoring an umbrella-shaped fold. The carboxyl-terminal motif uses puckering of the tyrosine side-chains as a unique docking arrangement in h elix termination. The structure provides an explanation for assembly and in sertion of the lipoprotein molecules into the outer membrane of gram-negati ve bacteria and suggests a molecular target for antibacterial drug discover y. (C) 2000 Academic Press.