title: Crystal structures of a quorum-quenching antibody.
abstract: A large number of Gram-negative bacteria employ N-acyl homoserine lactones (AHLs) as signaling molecules in quorum sensing, which is a population density-dependent mechanism to coordinate gene expression. Antibody RS2-1G9 was elicited against a lactam mimetic of the N-acyl homoserine lactone and represents the only reported monoclonal antibody that recognizes the naturally-occuring N-acyl homoserine lactone with high affinity. Due to its high cross-reactivity, RS2-1G9 showed remarkable inhibition of quorum sensing signaling in Pseudomonas aeruginosa, a common opportunistic pathogen in humans. The crystal structure of Fab RS2-1G9 in complex with a lactam analog revealed complete encapsulation of the polar lactam moiety in the antibody-combining site. This mode of recognition provides an elegant immunological solution for tight binding to an aliphatic, lipid-like ligand with a small head group lacking typical haptenic features, such as aromaticity or charge, which are often incorporated into hapten design to generate high-affinity antibodies. The ability of RS2-1G9 to discriminate between closely related AHLs is conferred by six hydrogen bonds to the ligand. Conversely, cross-reactivity of RS2-1G9 towards the lactone is likely to originate from conservation of these hydrogen bonds as well as an additional hydrogen bond to the oxygen of the lactone ring. A short, narrow tunnel exiting at the protein surface harbors a portion of the acyl chain and would not allow entry of the head group. The crystal structure of the antibody without its cognate lactam or lactone ligands revealed a considerably altered antibody-combining site with a closed binding pocket. Curiously, a completely buried ethylene glycol molecule mimics the lactam ring and, thus, serves as a surrogate ligand. The detailed structural delineation of this quorum-quenching antibody will aid further development of an antibody-based therapy against bacterial pathogens by interference with quorum sensing.
authors.affiliation: Department of Molecular Biology and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: Erik W
authors.initials: EW
authors.lastname: Debler
authors.forename: Gunnar F
authors.initials: GF
authors.lastname: Kaufmann
authors.forename: Robert N
authors.initials: RN
authors.lastname: Kirchdoerfer
authors.forename: Jenny M
authors.initials: JM
authors.lastname: Mee
authors.forename: Kim D
authors.initials: KD
authors.lastname: Janda
authors.forename: Ian A
authors.initials: IA
authors.lastname: Wilson
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D019855:Ethylene Glycol / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D015394:Molecular Structure; D015202:Protein Engineering; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D000911:Antibodies, Monoclonal; D007140:Immunoglobulin Fab Fragments; C088386:homoserine lactone; D019855:Ethylene Glycol; D015107:4-Butyrolactone