Back-fusion is the fusion of internal (intraluminal) vesicles within

multivesicular bodies Endosomes are a collection of intracellular sorting organelles in eukaryotic cells. They are parts of endocytic membrane transport pathway originating from the trans Golgi network. Molecules or ligands internalized from the plasma membrane can f ...

or late

endosome Endosomes are a collection of intracellular sorting organelles in eukaryotic cells. They are parts of endocytic membrane transport pathway originating from the trans Golgi network. Molecules or ligands internalized from the plasma membrane c ...

s with the endosome’s limiting membrane. The process is believed to be mediated by lysobiphosphatidic acid (LBPA), phosphatidylinositol-3-phosphate, Alix, and an apparent dependence on an acidic pH. MHC class 2 and other proteins (CD63 and MPR) utilize such a process to effectively transport to locations in the

cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...

and back to the

plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

. However,

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...

s also exploit this mechanism to efficiently enter the cytosol of the cell (e.g. VSV,

anthrax Anthrax is an infection caused by the bacterium '' Bacillus anthracis''. It can occur in four forms: skin, lungs, intestinal, and injection. Symptom onset occurs between one day and more than two months after the infection is contracted. The s ...

). Unlike regular fusion in the cell between endosomes and

organelle In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' t ...

s, back-fusion requires the exoplasmic leaflets of the internal vesicles and outer membrane to fuse - similar to sperm-egg fusion.

Notes

{{Reflist, 2 Cell anatomy