Gram-negative bacteria characteristically are surrounded by an additional membrane layer, the outer membrane. Although outer membrane components often play important roles in the interaction of symbiotic or pathogenic bacteria with their host organisms, the major role of this membrane must usually be to serve as a permeability barrier to prevent the entry of noxious compounds and at the same time to allow the influx of nutrient molecules. This review summarizes the development in the field since our previous review (H. Nikaido and M. Vaara, Microbiol. Rev. 49:1-32, 1985) was published. With the discovery of protein channels, structural knowledge enables us to understand in molecular detail how porins, specific channels, TonB-linked receptors, and other proteins function. We are now beginning to see how the export of large proteins occurs across the outer membrane. With our knowledge of the lipopolysaccharide-phospholipid asymmetric bilayer of the outer membrane, we are finally beginning to understand how this bilayer can retard the entry of lipophilic compounds, owing to our increasing knowledge about the chemistry of lipopolysaccharide from diverse organisms and the way in which lipopolysaccharide structure is modified by environmental conditions.

Molecular Basis of Bacterial Outer Membrane Permeability Revisited

Outer Membrane Permeability and Antibiotic Resistance

The outer membrane protects Gram-negative bacteria against a harsh environment. At the same time, the embedded proteins fulfil a number of tasks that are crucial to the bacterial cell, such as solute and protein translocation, as well as signal transduction. Unlike membrane proteins from all other sources, integral outer membrane proteins do not consist of transmembrane alpha-helices, but instead fold into antiparallel beta-barrels. Over recent years, the atomic structures of several outer membrane proteins, belonging to six families, have been determined. They include the OmpA membrane domain, the OmpX protein, phospholipase A, general porins (OmpF, PhoE), substrate-specific porins (LamB, ScrY) and the TonB-dependent iron siderophore transporters FhuA and FepA. These crystallographic studies have yielded invaluable insight into and decisively advanced the understanding of the functions of these intriguing proteins. Our review is aimed at discussing their common principles and peculiarities as well as open questions associated with them.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2958.2000.01983.x

Structure and function of bacterial outer membrane proteins: barrels in a nutshell

Conformational constraints for amyloid fibrillation: the importance of being unfolded.

Amyloid fibrils and prions are proteinaceous aggregates that are based on a unique form of polypeptide configuration, termed cross-β structure. Using a group of chemically distinct polyamino acids, we show here that the existence of such a structure does not require the presence of specific side chain interactions or sequence patterns. These observations firmly establish that amyloid formation and protein folding represent two fundamentally different ways of organizing polypeptides into ordered conformations. Protein folding depends critically on the presence of distinctive side chain sequences and produces a unique globular fold. By contrast, the properties of different polyamino acids suggest that amyloid formation arises primarily from main chain interactions that are, in some environments, overruled by specific side chain contacts. This side chain effect can be thought of as the inverse of the one that characterizes protein folding. Conditions including Alzheimer’s and Creutzfeldt–Jakob diseases represent, on this basis, pathological cases in which a natural polypeptide chain has aberrantly adopted the conformation that is primarily defined by main chain interactions and not the structure that is determined by specific side chain contacts that depend on the polypeptide sequence.

/pdf/the-behaviour-of-polyamino-acids-reveals-an-inverse-side-3v9jo27cl7.pdf

The behaviour of polyamino acids reveals an inverse side chain effect in amyloid structure formation.

http://www.jbc.org/content/271/34/20676.full.pdf

Structural and Functional Characterization of OmpF Porin Mutants Selected for Larger Pore Size II. FUNCTIONAL CHARACTERIZATION

Dedication Preface 1. Introduction 2. The diversity of membrane lipids 3. Tools for studying membrane components 4. Proteins in or at the bilayer 5. Bundles and barrels 6. Functions and families 7. Protein folding and biogenesis 8. Diffraction and simulation 9. Membrane enzymes 10. Membrane receptors 11. Transporters 12. Channels 13. Electron transport and energy transduction 14. In pursuit of complexity Appendix I. Abbreviations Appendix II. Single-letter codes for amino acids Index.

Membrane Structural Biology: With Biochemical and Biophysical Foundations

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/S0014-5793%2800%2901184-4

A peptide from the adenovirus fiber shaft forms amyloid-type fibrils

Role of a disulfide bond in the thermal stability of the LamB protein trimer in Escherichia coli outer membrane

Folding studies of purified LamB protein, the maltoporin from the Escherichia coli outer membrane: trimer dissociation can be separated from unfolding.

Mary Luckey

Papers

Structural and Functional Characterization of OmpF Porin Mutants Selected for Larger Pore Size II. FUNCTIONAL CHARACTERIZATION

Membrane Structural Biology: With Biochemical and Biophysical Foundations

A peptide from the adenovirus fiber shaft forms amyloid-type fibrils

Role of a disulfide bond in the thermal stability of the LamB protein trimer in Escherichia coli outer membrane

Folding studies of purified LamB protein, the maltoporin from the Escherichia coli outer membrane: trimer dissociation can be separated from unfolding.