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Publication Abstract from PubMed

In many Gram-negative bacteria, the peptidoglycan synthase PBP1A requires the outer membrane lipoprotein LpoA for constructing a functional peptidoglycan required for bacterial viability. Previously, we have shown that the C-terminal domain of Haemophilus influenzae LpoA (HiLpoA) has a highly conserved, putative substrate-binding cleft between two alpha/beta lobes. Here, we report a 2.0-A-resolution crystal structure of the HiLpoA N-terminal domain. Two subdomains contain tetratricopeptide-like motifs that form a concave groove, but their relative orientation differs by ~45 degrees from that observed in an NMR structure of the Escherichia coli LpoA N domain. We also determined three 2.0-2.8-A-resolution crystal structures containing four independent full-length HiLpoA molecules. In contrast to an elongated model previously suggested for E. coli LpoA, each HiLpoA formed a U-shaped structure with a different C-domain orientation. This resulted from both N-domain twisting and rotation of the C domain (up to 30 degrees ) at the end of the relatively immobile interdomain linker. Moreover, a previously predicted hinge between the lobes of the LpoA C domain exhibited variations of up to 12 degrees . Small-angle X-ray scattering (SAXS) data revealed excellent agreement with a model calculated by normal mode analysis (NMA) from one of the full-length HiLpoA molecules, but even better agreement with an ensemble of this molecule and two of the partially extended NMA-predicted models. The different LpoA structures helped explain how an outer membrane-anchored LpoA can either withdraw from or extend toward the inner membrane-bound PBP1A through peptidoglycan gaps and hence regulate the synthesis of peptidoglycan necessary for bacterial viability.

Structural analyses of the Haemophilus influenzae peptidoglycan synthase activator LpoA suggest multiple conformations in solution.,Sathiyamoorthy K, Vijayalakshmi J, Tirupati B, Fan L, Saper MA J Biol Chem. 2017 Sep 8. pii: jbc.M117.804997. doi: 10.1074/jbc.M117.804997. PMID:28887305^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.