Porosome
Encyclopedia
Porosomes or fusion pores are cup-shaped structures in the cell membranes of eukaryotic
cells where vesicles
dock in the process of vesicle fusion
and secretion. These structures are about 150 nanometers in diameter and contain many different types of protein, especially SNARE proteins
that mediate the docking and fusion of the vesicles with the cell membrane. Once the vesicles have docked with the SNARE proteins, they swell, which increases their internal pressure. They then fuse with the membrane, and these pressurized contents are ejected from the cell.
Porosomes vary in size depending on what cell they are on; pancreatic porosomes range from 100 nm to 180 nm in diameter while in neurons they range from 10 nm to 15 nm (about 1/10 the size of pancreatic porosomes). When a secretory vesicle containing v-SNARE is located opposite to the porosome containing t-SNARE, membrane continuity (ring complex) is formed between the two. The size of the t/v-SNARE complex is directly proportional to the size of the vesicle. These vesicles contain dehydrated proteins (non-active) which are activated once they are hydrated. Once the vesicle and the porosome form a complex, GTP is needed for active transport through the water channel into the vesicle and to turn on the ion channels. This results in vesicle swelling and an increase in turgor pressure which, in turn, result in the secretion of the contents.
Generally the vesicles are opened and closed by actin, but neurons require a fast response therefore they have central plugs that open to release contents and close to stop the release (the composition of the central plug is yet to be discovered).
at Yale University
School of Medicine, using atomic force microscopy. Dr. Bhanu Jena is the "Distinguished Professor of Physiology" at the Wayne State University School of Medicine
.
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
cells where vesicles
Vesicle (biology)
A vesicle is a bubble of liquid within another liquid, a supramolecular assembly made up of many different molecules. More technically, a vesicle is a small membrane-enclosed sack that can store or transport substances. Vesicles can form naturally because of the properties of lipid membranes , or...
dock in the process of vesicle fusion
Vesicle fusion
Vesicle fusion is the merging of a vesicle with other vesicles or a part of a cell membrane. In the latter case, it is the end stage of secretion from secretory vesicles, where their contents are expelled from the cell through exocytosis at the porosome...
and secretion. These structures are about 150 nanometers in diameter and contain many different types of protein, especially SNARE proteins
SNARE (protein)
SNARE proteins are a large protein superfamily consisting of more than 60 members in yeast and mammalian cells....
that mediate the docking and fusion of the vesicles with the cell membrane. Once the vesicles have docked with the SNARE proteins, they swell, which increases their internal pressure. They then fuse with the membrane, and these pressurized contents are ejected from the cell.
Porosomes vary in size depending on what cell they are on; pancreatic porosomes range from 100 nm to 180 nm in diameter while in neurons they range from 10 nm to 15 nm (about 1/10 the size of pancreatic porosomes). When a secretory vesicle containing v-SNARE is located opposite to the porosome containing t-SNARE, membrane continuity (ring complex) is formed between the two. The size of the t/v-SNARE complex is directly proportional to the size of the vesicle. These vesicles contain dehydrated proteins (non-active) which are activated once they are hydrated. Once the vesicle and the porosome form a complex, GTP is needed for active transport through the water channel into the vesicle and to turn on the ion channels. This results in vesicle swelling and an increase in turgor pressure which, in turn, result in the secretion of the contents.
Generally the vesicles are opened and closed by actin, but neurons require a fast response therefore they have central plugs that open to release contents and close to stop the release (the composition of the central plug is yet to be discovered).
History of discovery
The porosome was discovered in the early to mid-1990s by a team led by Professor Bhanu Pratap JenaBhanu Pratap Jena
Bhanu Pratap Jena is an American cell biologist and the " George E. Palade University Professor and Distinguished Professor of Physiology" at the Wayne State University School of Medicine, who in the mid 90’s discovered the Porosome, demonstrated to be the universal secretory machinery at the...
at Yale University
Yale University
Yale University is a private, Ivy League university located in New Haven, Connecticut, United States. Founded in 1701 in the Colony of Connecticut, the university is the third-oldest institution of higher education in the United States...
School of Medicine, using atomic force microscopy. Dr. Bhanu Jena is the "Distinguished Professor of Physiology" at the Wayne State University School of Medicine
Wayne State University School of Medicine
The Wayne State University School of Medicine is the largest single-campus medical school in the United States with more than 1,000 medical students. In addition to undergraduate medical education, the school offers master’s degree, Ph.D., and M.D.-Ph.D. programs in 14 areas of basic science to...
.
External links
- Molecular Machinery & Mechanism of Cell Secretion Jena Lab at Wayne State University School of Medicine