Gram-negative bacteria periplasm

Gram-negative organisms produce ced-bound P-lactamases which reside in the periplasmic space. Thus, for gram-negative bacteria, the antibiotic must penetrate the outer ced membrane/wad before coming in contact with a P-lactamase (80,139,140). 

Gram-negative bacteria are surrounded by two membranes, an inner plasma membrane and an outer membrane. These are separated by a periplasmic space. Most plasma membrane proteins contain long, continuous sequences of about 20 hydrophobic residues that are typical of transmembrane a helices such as those found in bacteriorhodopsin. In contrast, most outer membrane proteins do not show such sequence patterns. 

Currently, five different molecular classes of mdr efflux pumps are known [5], While pumps of the the ATP-binding cassette (ABC) transporter superfamily are driven by ATP hydrolysis, the other four superfamilies called resistance-nodulation-division (RND), major facilitator superfamily (MFS), multidrug and toxic compound extrusion (MATE), and small multidrag resistance transporter (SMR) are driven by the proton-motive force across the cytoplasmic membrane. Usually a single pump protein is located within the cytoplasmic membrane. However, the RND-type pumps which are restricted to Gram-negative bacteria consist of two additional components, a periplasmic membrane fusion protein (MFP) which connects the efflux pump to an outer... 

In Gram-negative bacteria, diffusion of (3-lactam antibiotics into the periplasm (where the activity of PBPs takes place) occurs via the channels that porins create in the outer membrane. The number and properties of the porin molecules are such that diffusion is relatively rapid in E. coli but much slower in Enterobacter and Pseudomonas. Mutants can be selected after the permeability of porin channels or their number has been decreased. A slow diffusion into... 

AGAC-modifying enzymes are active outside the cytoplasmic membrane, in the periplasmic space in Gram-negative bacteria and extracellularly in Gram-positives. Table 9.4 summarizes some of the enzymes involved in AGAC resistance and their spectrum of activity. 

E. coli, like other Gram-negative bacteria, has an outer membrane which hampers excretion of proteins to the culture media. Thus, expressed proteins can remain in the cytoplasm or can be directed into the periplasm employing the N-terminus fusion of a signal peptide (e.g. OmpA, pelB, OmpF, PhoA, Tat signal peptides) [30]. 

In Gram-negative bacteria which are characterised by a rather complex cell envelope, the CM is also referred to as inner membrane to distinguish it from a second lipid bilayer, termed outer membrane (OM). The space between these two layers is called the periplasm (PP). In the periplasmic space, many proteins are found with a variety of functions. Some are involved in biosynthesis and/or export of cell wall components and surface structures (e.g. pili, flagellae,... 

Forward, J. A., Behrendt, M. C., Wyborn, N. R., Cross, R. and Kelly, D. J. (1997). TRAP transporters a new family of periplasmic solute transport systems encoded by the dctPQM genes of Rhodobacter capsulatus and by homologs in diverse gram-negative bacteria, J. Bacteriol., 179, 5482-5493. 

The uptake of siderophore-iron complexes by Gram-negative bacteria is energy dependent and occurs via specific outer membrane proteins. In the periplasmic space, it binds to its cognate periplasmic binding protein and is then actively transported across the cytoplasmic membrane by an ATP-trans-porter protein. Three principal mechanisms for transport through the outer membrane have been described ... 

Fig. 2. The periplasmic location in Gram-negative bacteria of the two diheme enzymes,...

It is nearly 50 years since a c-type cytochrome was shown to catalyze peroxidase activity in crude extracts of Pseudomonas fluorescens (40). The enzyme responsible was first purified some 20 years later by Ell-folk and Soninen from the closely related P. aeruginosa and shown to be a diheme cytochrome c peroxidase (CCP) (41). These bacterial diheme CCPs are quite distinct from the superfamily of plant and yeast peroxidases (42) and are widely distributed among the Gram-negative bacteria (41, 43 6). Diheme CCPs are located in the periplasm (Fig. 2), where they catalyze the two-electron reduction of H2O2 to H2O by soluble one-electron donors such as cytochromes c and cupredoxins. 

When deficient in iron, bacteria and fungi produce and excrete to the extracellular medium low molecular weight, specific iron-carrier molecules, called siderophores. These siderophores bind ferric ions, to form soluble complexes. The complexed ferric ions are transported into the cell through high-affinity and energy-dependent receptor proteins located on the outer membrane. In Gram-negative bacteria, such as E. coli, the most studied system, siderophore-iron complexes are transported initially to the periplasm. 

Denitrifying bacteria produce one or the other of two usually soluble but very dissimilar nitrite reductases, heme- and Cu-containing types (Brittain et al., 1992 Coyne et al., 1989), both of which are found in the periplasmic space of gram-negative bacteria (Coyne et al., 1990). 

Although the Cu-type family of nitrite reductase is comprised of soluble enzyme and localized in the periplasmic space in gram-negative bacteria, it has proved to be a membrane-bound enzyme in denitrifying Bacillus, which is gram positive and lacks an outer membrane and periplasmic space (Denariaz et ai, 1991 Urata and Satoh, 1991 Ho etal., 1993). 

Figure 17.13 Barriers separating periplasmic enzymes (gram-negative bacteria) and cytoplasmic enzymes (gram-negative and grampositive bacteria) from substrates in the surrounding environment (Madigan et al., 2000).

Periplasmic permeases. Gram-negative bacteria contain numerous ABC transporters with components located on the periplasmic surfaces of their plasma membranes. Many of these can be dissociated from the surfaces by osmotic shock, i.e., by sudden changes in the osmotic pressure of the medium.451 452 For example, cells of E. coli suspended in 0.5 M sucrose, treated with 10 4 M EDTA for 10 min, and then diluted... 

The plasma membrane of bacterial cells, other than the wall-less mycoplasmas and some archaebacteria, is surrounded by a multilayered wall which may be separated from the membrane by a thin periplasm (or periplasmic space). This can be seen most clearly in suitably prepared thin sections of cells of E. coli or other gram-negative bacteria as a relatively empty space of 11- to 25-nm thickness (Fig. 8-28).579 581 The volume of this space (which may be filled with gelled material) depends upon the osmotic pressure of the medium. In E. coli it contains 20-40% of the total... 

The outer membrane of Gram-negative bacteria is spanned by porins, trimeric proteins that form inlet channels between the outer membrane and the periplasmic space. The geometry of the porins defines the substrate uptake limit, which is on the order of 600 daltons (Weiss et al., 1991), approximately equivalent to a trisaccharide. Substrates larger than this limit (with few exceptions) must be hydrolyzed outside the outer membrane prior to uptake. Extracellular hydrolysis is carried out by means of extracellular en-... 

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