Most bacteria surround themselves with a cell wall, a strong meshwork consisting primarily of the polymerized aminosugar peptidoglycan (PG). PG is essential for structural maintenance of bacterial cells, and thus for viability. PG is also constantly synthesized and turned over; the latter process is mediated by PG cleavage enzymes, for example, the endopeptidases (EPs). EPs themselves are essential for growth but also promote lethal cell wall degradation after exposure to antibiotics that inhibit PG synthases (e.g., β-lactams). Thus, EPs are attractive targets for novel antibiotics and their adjuvants. However, we have a poor understanding of how these enzymes are regulated in vivo, depriving us of novel pathways for the development of such antibiotics. Here, we have solved crystal structures of the LysM/M23 family peptidase ShyA, the primary EP of the cholera pathogenVibrio cholerae. Our data suggest that ShyA assumes two drastically different conformations: a more open form that allows for substrate binding and a closed form, which we predicted to be catalytically inactive. Mutations expected to promote the open conformation caused enhanced activity in vitro and in vivo, and these results were recapitulated in EPs from the divergent pathogensNeisseria gonorrheaeandEscherichia coli. Our results suggest that LysM/M23 EPs are regulated via release of the inhibitory Domain 1 from the M23 active site, likely through conformational rearrangement in vivo.

Coexistence holes characterize the assembly and disassembly of multispecies systemsThe MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters.

A central goal of life science has been to understand the limits of species coexistence. However, we know surprisingly little about the structure of species coexistence below such limits, and how it affects the assembly and disassembly of ecological systems. Here we introduce a novel hypergraph-based formalism that fully captures the structure of coexistence in multispecies systems. Our formalism uncovers that, below its limits, coexistence in ecological systems has ubiquitous discontinuities that we call "coexistence holes." These coexistence holes do not occur arbitrarily but tend to obey patterns that make them predictable. We provide direct evidence showing that the biotic and abiotic constraints of empirical systems produce an over-representation of coexistence holes. By highlighting discontinuities in the form of coexistence holes, our work provides a new platform to uncover the order and structure of the assembly and disassembly of ecological systems.

The bacterial periplasmic protein LpoA is an outer membrane lipoprotein and an activator for the cross-linking activity of PBP1A, a bifunctional peptidoglycan synthase. Previous structures of the amino-terminal (N) domain of LpoA showed it to consist entirely of helices and loops, with at least four tetratricopeptide-like repeats. Although the previously determined orthorhombic crystal structure of the N domain of Haemophilus influenzae LpoA showed a typical curved structure with a concave groove, an NMR structure of the same domain from Escherichia coli was relatively flat. Here, a crystal structure of the N domain of E. coli LpoA was determined to a resolution of 2.1 Å and was found to be more similar to the H. influenzae crystal structure than to the E. coli NMR structure. To provide a quantitative description for these comparisons, the various structures were superimposed pairwise by fitting the first half of each structure to its pairwise partner and then calculating the rotation axis that would optimally superimpose the second half. Differences in both the magnitude of the rotation and the direction of the rotation axis were observed between different pairs of structures. A 1.35 Å resolution structure of a monoclinic crystal form of the N domain of H. influenzae LpoA was also determined. In this structure, the subdomains rotate 10 relative to those in the original orthorhombic H. influenzae crystal structure to further narrow the groove between the subdomains. To accommodate this, a bound chloride ion (in place of sulfate) allowed the closer approach of a helix that forms one side of the groove.