The plasma membrane is the interface between cells and their harsh environment. Uptake of nutrients and all communication among cells and between cells and their environment occurs through this interface. 'Endocytosis' encompasses several diverse mechanisms by which cells internalize macromolecules and particles into transport vesicles derived from the plasma membrane. It controls entry into the cell and has a crucial role in development, the immune response, neurotransmission, intercellular communication, signal transduction, and cellular and organismal homeostasis. As the complexity of molecular interactions governing endocytosis are revealed, it has become increasingly clear that it is tightly coordinated and coupled with overall cell physiology and thus, must be viewed in a broader context than simple vesicular trafficking.

Regulated portals of entry into the cell

Molecular basis of bacterial outer membrane permeability.

The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis an...

http://www.afboard.com/library/creatinemetabolism.pdf

Creatine and Creatinine Metabolism

Production of large unilamellar vesicles by a rapid extrusion procedure. Characterization of size distribution, trapped volume and ability to maintain a membrane potential

Bacteriocins are bacterially produced antimicrobial peptides with narrow or broad host ranges. Many bacteriocins are produced by food-grade lactic acid bacteria, a phenomenon which offers food scientists the possibility of directing or preventing the development of specific bacterial species in food. This can be particularly useful in preservation or food safety applications, but also has implications for the development of desirable flora in fermented food. In this sense, bacteriocins can be used to confer a rudimentary form of innate immunity to foodstuffs, helping processors extend their control over the food flora long after manufacture.

Bacteriocins: developing innate immunity for food

To analyze proteins interacting at the membrane interface, a phospholipid analogue was used with a photoactivatable headgroup (ASA-DLPE, N-(4-azidosalicylamidyl)-1,2-dilauroyl-sn-glycero-3-phosphoethanolamine) for selective cross-linking. The peripheral membrane protein cytochrome c from the inner mitochondrial membrane was rendered carbonate wash-resistant by cross-linking to ASA-DLPE in a model membrane system, validating our approach. Cross-link products of cytochrome c and its precursor apocytochrome c were demonstrated by matrix-assisted laser desorption/ionization timeof-flight mass spectrometry (MALDI-TOF MS) and were specifically detected by sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE), taking advantage of the intrinsic UV absorbance of the cross-linker. Application of the method to inner mitochondrial membranes from Saccharomyces cerevisae revealed cross-link products of both exogenously added apocytochrome c and endogenous proteins with molecular weights around 34 and 72 kDa. Liquid chromatograpy (LC)-MS/MS was performed to identify these proteins, resulting in a list of candidate proteins potentially cross-linked at the membrane interface. The approach described here provides methodology for capturing phospholipid-protein interactions in their native environment of the biomembrane using modern proteomics techniques.

https://dspace.library.uu.nl/bitstream/handle/1874/26331/13_probing_gubbens.pdf;sequence=1

Probing the membrane interface-interacting proteome using photoactivatable lipid cross-linkers.

In the last decade the fluid mosaic model (Singer and Nicholson 1972) of biological membranes has become generally accepted as it provided a rationale for many structural and functional features of membranes. More recently, however it has become increasingly clear that this model is incomplete for reasons relating to lipid composition as well as functional abilities of biological membranes. First, although the chemical variation in membrane lipids is enormous, it is surprising that most of them can be divided into only two groups on structural grounds: The lipids of the first group, including PC* and sphingomyelin, will organize themselves in bilayers when they are in the fully hydrated state (bilayer lipids). It is obvious that this property has greatly contributed to the bilayer concept of biological membranes. In contrast, the lipids in the second group do not form bilayers when they are dispersed in excess buffer (non-bilayer lipids). This group includes major lipids such as PE*, monoglucosyl and monogalactosyl diglyceride and CL4 (in the presence of Ca2+) (for review and references see Cullis and de Kruijff 1979). These lipids prefer the hexagonal HII, phase (Fig. 1). This phase consists of cylinders of lipids surrounding long aqueous channels. The unique feature of the HII phase both from a structural and functional point of view is that it allows polar lipids to be organized in a low energy configuration inside a hydrophobic environment. The reason for the abundant presence of these non-bilayer lipids in membranes is difficult to understand in terms of membrane models in which the bilayer is suggested to be the only organization available to the lipids.

Non-bilayer Lipids and the Inner Mitochondrial Membrane

To study the structural change of diphtheria toxin (DT) induced by low pH and its influence on the interaction with membrane lipids, protein and lipid monolayers were formed and characterized. DT at neutral and acidic pH forms stable monolayers, whose surface-pressure-increase curves allow an estimation of the apparent molecular area of 29.5 nm2/molecule at pH 7.4 (corresponding to a radius of 3.06 nm) and 34.5 nm2/molecule at pH 5.0 (corresponding to a radius of 3.32 nm). DT at pH 7.4 does not insert into phospholipid monolayers, while at pH 5.0 it penetrates into the lipid layer with a portion of apparent molecular area of 21.0 nm2/molecule (corresponding to a radius of 2.6 nm). The low-pH driven lipid interaction of the toxin is favoured by the presence of acidic phospholipids, without an apparent requirement for a particular class of negative lipids. The DT mutants crm 45 and crm 197 are capable of hydrophobic interaction already at neutral pH and cause an increase of surface pressure with a further increase upon acidification.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1991.tb15935.x

Lipid interaction of diphtheria toxin and mutants. A study with phospholipid and protein monolayers.

We have used acylated analogs of gramicidin as a model to study the interaction between a covalently coupled fatty acid and the hydrophobic part of a membrane-spanning protein in a bilayer environment. The acyl chain was covalently coupled to the C-terminal ethanolamine group of gramicidin which is located near the membrane interface, mimicking a situation found in acylated proteins. Either perdeuterated palmitic acid or palmitic acid deuterated at only C2, C3, C5-6, C7-8, C9, or C13 was coupled to gramicidin and examined by 2H-NMR in oriented bilayers of dimyristoylphosphatidylcholine. In this way, quadrupolar splittings of deuterons at specific carbons were assigned. The quadrupolar splittings and T1 values were compared to those of free palmitic acid in oriented bilayers, with and without gramicidin. The results indicate that the covalently coupled fatty acid is highly immobilized near the carboxyl terminus because double quadrupolar splittings and very low T1 values (4 ms) were found for the -CD2- deuterons at carbon atoms C2 and C3. Control experiments with free fatty acid showed single quadrupolar splittings and higher T1 values for this segment of the fatty acid. Molecular modeling of the carboxy-terminal segment of the covalently coupled acyl chain suggested that it has a defined structure with a bend near its attachment site. In contrast, the methyl end (C10-C16) of the covalently coupled fatty acid had quadrupolar splittings and T1 values very similar to those found for free fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure and dynamics of the acyl chain of a transmembrane polypeptide.

Relationship between gramacidin conformation dependent induction of phospholipid transbilayer movement and hexagonal HII phase formation in erythrocyte membranes

B. de Kruijff

Papers

Probing the membrane interface-interacting proteome using photoactivatable lipid cross-linkers.

Non-bilayer Lipids and the Inner Mitochondrial Membrane

Lipid interaction of diphtheria toxin and mutants. A study with phospholipid and protein monolayers.

Structure and dynamics of the acyl chain of a transmembrane polypeptide.

Relationship between gramacidin conformation dependent induction of phospholipid transbilayer movement and hexagonal HII phase formation in erythrocyte membranes