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For example, an S-layer could conceivably keep extracellular proteins near the cell membrane by preventing their diffusion away from the cell. In some pathogenic species, an S-layer may help to facilitate survival within the host by conferring protection against host defence mechanisms.
Intracellular bacteria are bacteria that have the capability to enter and survive within the cells of the host organism. [1] These bacteria include many different pathogens that live in the cytoplasm and nuclei of the host cell's they inhabit. Two examples of intracellular pathogenic bacteria are Mycobacterium tuberculosis and also Toxoplasma ...
When an intracellular parasite goes to enter a host cell, it is particular about the type of host cell. This is because most intracellular parasites are able to infect only a few different cell types. [21] Viruses use a number of host receptors to gain entry to the cell, usually by causing endocytosis. [7]
The general secretion (Sec) involves secretion of unfolded proteins that first remain inside the cells. In Gram-negative bacteria, the secreted protein is sent to either the inner membrane or the periplasm. But in Gram-positive bacteria, the protein can stay in the cell or is mostly transported out of the bacteria using other secretion systems.
While in the human host, the parasite spends most of its life cycle within hepatic cells and erythrocytes (in contrast to T. brucei which remains extracellular). As a result of its mainly intracellular niche, parasitized host cells which display parasite proteins must be modified to prevent destruction by the host immune defenses.
Instead, the extracellular forms of these Gram-negative bacteria maintain their structural integrity by relying on a layer of disulfide bond cross-linked cysteine-rich proteins, which is located between cytoplasmic membrane and outer membrane in a manner analogous to the peptidoglycan layer in other Gram-negative bacteria. [4]
Bacteria produce various adhesins including lipoteichoic acid, trimeric autotransporter adhesins and a wide variety of other surface proteins to attach to host tissue. Capsules, made of carbohydrate, form part of the outer structure of many bacterial cells including Neisseria meningitidis .
Like these other systems, the type II secretion system enables the transport of cytoplasmic proteins across the lipid bilayers that make up the cell membranes of Gram-negative bacteria. Secretion of proteins and effector molecules out of the cell plays a critical role in signaling other cells and in the invasion and parasitism of host cells.