Бактериялардың периплазмасы: құрылымы және қызметтері

The region between the inner and outer membrane, or cell wall
The periplasm is a concentrated gel like matrix in the space between the inner cytoplasmic membrane and the bacterial outer membrane called the periplasmic space in gram negative (more accurately "diderm") bacteria. Using cryo electron microscopy it has been found that a much smaller periplasmic space is also present in gram positive bacteria (more accurately "monoderm"), between cell wall and the plasma membrane. The periplasm may constitute up to 40% of the total cell volume of gram negative bacteria, but is a much smaller percentage in gram positive bacteria.

Although bacteria are conventionally divided into two main groups—gram positive and gram negative, based upon their Gram stain retention property—this classification system is ambiguous as it can refer to three distinct aspects (staining result, cell envelope organization, taxonomic group), which do not necessarily coalesce for some bacterial species. In most situations such as in this article, gram staining reflects the marked differences in the ultrastructure and chemical composition of the two main kinds of bacteria. The usual "gram positive" type does not have an outer lipid membrane, while the typical "gram negative" bacterium does. The terms "diderm" and "monoderm", coined to refer to this distinction only, is a more reliable and fundamental characteristic of the bacterial cells. [[File:Gram Cell wall. svg|thumb|Monoderm bacteria have a thin periplasm between the cell wall and the plasma membrane

As shown in the figure to the right, the periplasmic space in gram negative or diderm bacteria is located between the inner and outer membrane of the cell. The periplasm contains peptidoglycan and the membranes that enclose the periplasmic space contain many integral membrane proteins, which can participate in cell signaling. Furthermore, the periplasm houses motility organelles such as the flagellum, which spans both membranes enclosing the periplasm. The periplasm is described as gel like due to the high abundance of proteins and peptidoglycan. The periplasm occupies 7% to 40% of the total volume of diderm bacteria, and contains up to 30% of cellular proteins. The structure of the monoderm periplasm differs from that of diderm bacteria as the so called periplasmic space in monoderm bacteria is not enclosed by two membranes but is rather enclosed by the cytoplasmic membrane and the peptidoglycan layer beneath. For this reason, the monoderm periplasmic space is also referred to as the inner wall zone (IWZ). The IWZ serves as the first destination of translocation for proteins being transported across the monoderm bacterial cell wall. Importantly, the periplasm is devoid of ATP. Several types of enzyme are present in the periplasm including alkaline phosphatases, cyclic phosphodiesterases, acid phosphatases and 5’ nucleotidases. Of note, the periplasm also contains enzymes important for the facilitation of protein folding. For example, disulfide bond protein A (DsbA) and disulfide bond protein C (DsbC), which are responsible for catalyzing peptide bond formation and isomerization, respectively, were identified in the periplasm of E. Coli. As disulfide bond formation is frequently a rate limiting step in the folding of proteins, these oxidizing enzymes play an important role in the bacteria periplasm. In addition, the periplasm mediates the uptake of DNA in several strains of transformable bacteria. [[File:Rcsfsignalingmechanism. jpg|thumb|Figure demonstrating modulation of RcsF signaling by changes in the periplasmic intermembrane distance Furthermore, the separation of the periplasm from the cytoplasm allows for the compartmentalization of enzymes that could be toxic in the cytoplasm. Gram negative bacteria tend to be more antimicrobial resistant than gram positive bacteria, and also possess a much more significant periplasmic space between their two membrane bilayers. Since eukaryotes do not possess a periplasmic space, structures and enzymes found in the gram negative periplasm are attractive targets for antimicrobial drug therapies. Additionally, vital functions such as facilitation of protein folding, protein transport, cell signaling, structural integrity, and nutrient uptake are performed by periplasm components, Due to their role in catalyzing disulfide bond formation for a variety of virulence factors, the DsbA/DsbB system has been of particular interest as a target for anti virulence drugs. The periplasmic space is deeply interconnected with the pathogenesis of disease in the setting of microbial infection. Many of the virulence factors associated with bacterial pathogenicity are secretion proteins, which are often subject to post translational modification including disulfide bond formation. The oxidative environment of the periplasm contains Dsb (disulfide bond formation) proteins that catalyze such post translational modifications, and therefore play an important role in establishing virulence factor tertiary and quaternary structure essential for proper protein function. Furthermore, the periplasm is also relevant to clinical developments by way of its role in mediating the uptake of transforming DNA.