Structural analysis of an “open” form of PBP1B from Streptococcus pneumoniae

Authors

  • Andrew L. Lovering,

    1. Department of Biochemistry and Molecular Biology, and the Center for Blood Research, University of British Columbia, Vancouver V6T 1R9, Canada
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  • Liza De Castro,

    1. Department of Biochemistry and Molecular Biology, and the Center for Blood Research, University of British Columbia, Vancouver V6T 1R9, Canada
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  • Daniel Lim,

    1. Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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  • Natalie C.J. Strynadka

    Corresponding author
    1. Department of Biochemistry and Molecular Biology, and the Center for Blood Research, University of British Columbia, Vancouver V6T 1R9, Canada
    • Department of Biochemistry and Molecular Biology, and the Center for Blood Research, University of British Columbia, 2350 Health Sciences Mall, Vancouver V6T 1R9, Canada; fax: (604) 822-5227.
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Abstract

The class A PBP1b from Streptococcus pneumoniae is responsible for glycosyltransferase and transpeptidase (TP) reactions, forming the peptidoglycan of the bacterial cell wall. The enzyme has been produced in a stable, soluble form and undergoes time-dependent proteolysis to leave an intact TP domain. Crystals of this TP domain were obtained, diffracting to 2.2 Å resolution, and the structure was solved by using molecular replacement. Analysis of the structure revealed an “open” active site, with important conformational differences to the previously determined “closed” apoenzyme. The active-site nucleophile, Ser460, is in an orientation that allows for acylation by β-lactams. Consistent with the productive conformation of the conserved active-site catalytic residues, adjacent loops show only minor deviation from those of known acyl-enzyme structures. These findings are discussed in the context of enzyme functionality and the possible conformational sampling of PBP1b between active and inactive states.

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