Synapto-pHluorin is a genetically encoded optical indicator of vesicle release and recycling. It is used in
neuroscience
Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, development ...
to study transmitter release. It consists of a pH-sensitive form of
green fluorescent protein
The green fluorescent protein (GFP) is a protein that exhibits bright green fluorescence when exposed to light in the blue to ultraviolet range. The label ''GFP'' traditionally refers to the protein first isolated from the jellyfish ''Aequorea ...
(GFP) fused to the luminal side of a
vesicle-associated membrane protein
Vesicle associated membrane proteins (VAMP) are a family of SNARE proteins with similar structure, and are mostly involved in vesicle fusion.
* VAMP1 and VAMP2 proteins known as synaptobrevins are expressed in brain and are constituents of th ...
(VAMP). At the acidic pH inside transmitter vesicles, synapto-pHluorin is non-fluorescent (
quenched
In materials science, quenching is the rapid cooling of a workpiece in water, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as phas ...
). When vesicles get released, synapto-pHluorin is exposed to the neutral extracellular space and the presynaptic terminal becomes brightly fluorescent. Following
endocytosis
Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material. E ...
, vesicles become re-acidified and the cycle can start again. Chemical
alkalinization of all vesicles is often used for normalization of the synapto-pHluorin signals. Synapto-pHluorin sometimes consists of
yellow fluorescent protein
Yellow fluorescent protein (YFP) is a genetic mutant of green fluorescent protein (GFP) originally derived from the jellyfish ''Aequorea victoria''. Its excitation peak is 513 nm and its emission peak is 527 nm. Like the parent GFP, YFP ...
(YFP) to monitor the cytoplasm because its
pKa is higher than GFP (7.1 versus 6.0).
History
Synapto-pHluorin was invented by
Gero Miesenböck
Gero Andreas Miesenböck (born 15 July 1965) is an Austrian scientist. He is currently Waynflete Professor of Physiology and Director of the Centre for Neural Circuits and Behaviour (CNCB) at the University of Oxford and a fellow of Magdalen C ...
in 1998. In 2006, an improved version was published, using
synaptophysin
Synaptophysin, also known as the major synaptic vesicle protein p38, is a protein that in humans is encoded by the ''SYP'' gene.
Genomics
The gene is located on the short arm of X chromosome (Xp11.23-p11.22). It is 12,406 bases in length and ...
to target the GFP to vesicles. In 2013, a two-color release sensor (ratio-sypHy) was introduced to determine the size of the
recycling pool at individual synapses.
Applications
Synapto-pHluorin is mainly used by neurobiologists to study transmitter release and
recycling
Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...
at
presynaptic terminals.
It has also been applied to the study of
insulin
Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism o ...
secretion in
beta cells
Beta cells (β-cells) are a type of cell found in pancreatic islets that synthesize and secrete insulin and amylin. Beta cells make up 50–70% of the cells in human islets. In patients with Type 1 diabetes, beta-cell mass and function are dimini ...
of the
pancreas
The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an end ...
.
References
{{Optogenetics
Protein methods
Recombinant proteins
Cell imaging
Fluorescent proteins