OmpA controls order in the outer membrane and shares the mechanical load

Only full-length OmpA contributes to cell strength. OmpA orders the OMP lattice and connects the OM and CW to form a mechanically strong composite. (A) Osmotic force extension was used to calculate the relative stiffness of ∆ompA, ompA1-191, and ompX-ompA192-346 cell envelopes, normalized to the WT (MG1655). This shows that all three strains are significantly softer than the WT (P < 0.003 by the one-sided t test). Center lines are meansand error bars are SD. ns = (P > 0.15) by the two-sample t test. (B) Schematic of predicted OM organization. The hexagonal lattice of trimeric porins (purple) is embedded with other OMPs (orange and brown), leaving gaps that are filled by the abundant OmpA (blue) which interacts with surrounding OMPs (red regions) while remaining in place, maintaining an ordered lattice. (C) OmpA is uniquely able to couple the compressive strength of the OMP lattice and tensile strength of the CW via β-barrel interaction, a flexible linker, and CW binding, allowing the whole cell envelope to act as a mechanically strong composite.

The Silhavy Lab at Princeton investigated the importance of the outer membrane in Gram-negative bacteria, its unique asymmetric structure with high protein content, and the abundance of outer membrane proteins like OmpA, OmpC, and OmpF, despite the molecular basis for OmpA's role remaining elusive.  They find:

- OmpA organizes the outer membrane protein lattice and mechanically connects it to the cell wall, forming a mechanically robust composite that increases the overall integrity of the bacterial cell envelope.

- This coupling between the compressive properties of the outer membrane protein lattice and the tensile strength of the cell wall is critical for the survival of bacteria.

- The mechanical coupling provided by OmpA allows the entire cell envelope to function as a cohesive, resilient structure.

OmpA acts as a small, stable fencepost that orders the outer membrane protein lattice and mechanically couples it to the cell wall, forming a composite material that is stronger than the individual components.

Benn G, Borrelli C, Prakaash D, Johnson ANT, Fideli VA, Starr T, Fitzmaurice D, Combs AN, Wühr M, Rojas ER, Khalid S, Hoogenboom BW, Silhavy TJ. OmpA controls order in the outer membrane and shares the mechanical load. Proc Natl Acad Sci U S A. 2024 Dec 10;121(50):e2416426121. doi: 10.1073/pnas.2416426121. Epub 2024 Dec 4. PMID: 39630873.     https://www.pnas.org/doi/full/10.1073/pnas.2416426121