Borrelia burgdorferi protein BBK32 binds to soluble fibronectin via the N-terminal 70-kDa region, causing fibronectin to undergo conformational extension

TY - JOUR

T1 - Borrelia burgdorferi protein BBK32 binds to soluble fibronectin via the N-terminal 70-kDa region, causing fibronectin to undergo conformational extension

AU - Harris, Gemma

AU - Ma, Wenjiang

AU - Maurer, Lisa M.

AU - Potts, Jennifer R.

AU - Mosher, Deane F.

N1 - © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.

PY - 2014/8/8

Y1 - 2014/8/8

N2 - BBK32 is a fibronectin (FN)-binding protein expressed on the cell surface of Borrelia burgdorferi, the causative agent of Lyme disease. There is conflicting information about where and how BBK32 interacts with FN. We have characterized interactions of a recombinant 86-mer polypeptide, "Bbk32," comprising the unstructured FN-binding region of BBK32. Competitive enzyme-linked assays utilizing various FN fragments and epitope-mapped anti-FN monoclonal antibodies showed that Bbk32 binding involves both the fibrin-binding and the gelatin-binding domains of the 70-kDa N-terminal region (FN70K). Crystallographic and NMR analyses of smaller Bbk32 peptides complexed, respectively, with (2-3)FNI and (8-9)FNI, demonstrated that binding occurs by β-strand addition. Isothermal titration calorimetry indicated that Bbk32 binds to isolated FN70K more tightly than to intact FN. In a competitive enzyme-linked binding assay, complex formation with Bbk32 enhanced binding of FN with mAbIII-10 to the (10)FNIII module. Thus, Bbk32 binds to multiple FN type 1 modules of the FN70K region by a tandem β-zipper mechanism, and in doing so increases accessibility of FNIII modules that interact with other ligands. The similarity in the FN-binding mechanism of BBK32 and previously studied streptococcal proteins suggests that the binding and associated conformational change of FN play a role in infection.

AB - BBK32 is a fibronectin (FN)-binding protein expressed on the cell surface of Borrelia burgdorferi, the causative agent of Lyme disease. There is conflicting information about where and how BBK32 interacts with FN. We have characterized interactions of a recombinant 86-mer polypeptide, "Bbk32," comprising the unstructured FN-binding region of BBK32. Competitive enzyme-linked assays utilizing various FN fragments and epitope-mapped anti-FN monoclonal antibodies showed that Bbk32 binding involves both the fibrin-binding and the gelatin-binding domains of the 70-kDa N-terminal region (FN70K). Crystallographic and NMR analyses of smaller Bbk32 peptides complexed, respectively, with (2-3)FNI and (8-9)FNI, demonstrated that binding occurs by β-strand addition. Isothermal titration calorimetry indicated that Bbk32 binds to isolated FN70K more tightly than to intact FN. In a competitive enzyme-linked binding assay, complex formation with Bbk32 enhanced binding of FN with mAbIII-10 to the (10)FNIII module. Thus, Bbk32 binds to multiple FN type 1 modules of the FN70K region by a tandem β-zipper mechanism, and in doing so increases accessibility of FNIII modules that interact with other ligands. The similarity in the FN-binding mechanism of BBK32 and previously studied streptococcal proteins suggests that the binding and associated conformational change of FN play a role in infection.

KW - Bacterial adhesion

KW - Fibronectin

KW - Protein conformation

KW - Protein crystallization

KW - Protein structure

KW - Host-pathogen interactions

KW - FNI modules

KW - Beta-zipper formation

KW - Borrelia burgdorferi

U2 - 10.1074/jbc.M114.578419

DO - 10.1074/jbc.M114.578419

M3 - Article

C2 - 24962582

SN - 1083-351X

VL - 289

SP - 22490

EP - 22499

JO - The Journal of biological chemistry

JF - The Journal of biological chemistry

IS - 32

ER -