PDBsum entry 1fj1

Immune system

PDB id

1fj1

Contents

			Protein chains

					213 a.a.


					213 a.a. *


					251 a.a. *

			Waters ×258

* Residue conservation analysis

References listed in PDB file

Key reference

Title

Structural identification of a key protective b-Cell epitope in lyme disease antigen ospa.

Authors

W.Ding, X.Huang, X.Yang, J.J.Dunn, B.J.Luft, S.Koide, C.L.Lawson.

Ref.

J Mol Biol, 2000, 302, 1153-1164. [DOI no: 10.1006/jmbi.2000.4119]

PubMed id

11183781

Abstract

Outer surface protein A (OspA) is a major lipoprotein of the Borrelia burgdorferi spirochete, the causative agent of Lyme disease. Vaccination with OspA generates an immune response that can prevent bacterial transmission to a mammalian host during the attachment of an infected tick. However, the protective capacity of immune sera cannot be predicted by measuring total anti-OspA antibody. The murine monoclonal antibody LA-2 defines an important protective B-cell epitope of OspA against which protective sera have strong levels of reactivity. We have now mapped the LA-2 epitope of OspA using both NMR chemical-shift perturbation measurements in solution and X-ray crystal structure determination. LA-2 recognizes the three surface-exposed loops of the C-terminal domain of OspA that are on the tip of the elongated molecule most distant from the lipid-modified N terminus. The structure suggests that the natural variation at OspA sequence position 208 in the first loop is a major limiting factor for antibody cross-reactivity between different Lyme disease-causing Borrelia strains. The unusual Fab-dominated lattice of the crystal also permits a rare view of antigen flexibility within an antigen:antibody complex. These results provide a rationale for improvements in OspA-based vaccines and suggest possible designs for more direct tests of antibody protective levels in vaccinated individuals.



	Figure 3. Figure 3. Structural comparison of NMR and crystallographic LA-2 epitope maps. (a) Schematic of OspA. The view is nearly "end-on", with the C-terminal domain of the molecule in the foreground. The polypeptide backbone is shown as a worm tube with labeled N and C-terminal ends. The three contiguous regions recognized by LA-2 are identified by blue, green, and magenta shading, respectively, and labeled by loop number as defined in the main text. The positions of Ala208 and Ala215 are indicated by red C^a-C^b bonds. Strictly conserved Trp216 on b-strand 17 is shown in cyan for reference. (b) By-residue NMR-chemical-shift perturbation data mapped onto the OspA structure, with non-hydrogen atoms shown as spheres (color scheme as in Figure 2). (c) Crystallographic identification of the LA-2 epitope. OspA atoms are shaded using a color gradient by their minimum distance from LA-2 atoms. Red, <3.5 Å; orange-bright yellow, 3.5-7.0 Å; yellow-faint yellow, 7.0-10 Å; white/gray, >10 Å. In (b) and (c), the C^b atoms of Ala208 and Ala215 are indicated with asterisks.		Figure 4. Figure 4. Schematic of the OspA/LA-2 Fab complex crystal lattice. The view is perpendicular to the crystallographic a-axis, and a one unit cell thick slice is shown. The b and c lattice repeats are indicated. The two LA-2 Fab dimers in the crystal asymmetric unit are indicated in light and dark gray, respectively. Two OspA/Fab complexes that define a single crystal asymmetric unit are shown in a thick trace. These two OspA molecules are shaded according to refined C^a-atom B-value (blue, B < 35 Å2; red, B > 65 Å2). This view highlights the alternating dense and sparsely packed molecular layers along the c-axis, corresponding to LA-2 Fab (gray) and OspA (green) layers, respectively. The 80 Å long OspA molecules are strongly anchored at their C-terminal tips to the Fab antigen combining sites, but they extend into the sparse layer where they are nearly entirely surrounded by solvent. Only one of the two OspAs in the asymmetric unit (lower OspA in this view) makes a weak bridging lattice contact with its N-terminal domain to the adjoining Fab layer, consisting of two salt bridges between flexible side-chains. These weak lattice contacts and corresponding thin-plate crystal morphology resulted in poor diffraction along the c*-axis.

PROCHECK

	Headers