leky-latky/gAD-glutamic-acid-decarboxylase/izoformy-formy-prekurzory-geny
Isoforms
- Molecular weights of 67 and 65 kDa (GAD67 and GAD65)
- Different genes on different chromosomes
- GAD1 and GAD2 genes
- Chromosomes 4 and 10
- GAD67 and GAD65 are expressed in
- Brain where GABA is used as a neurotransmitter
- Insulin-producing ß-cells of the pancreas
- Truncated transcripts and polypeptides of GAD67
- Detectable in the developing brain - function unknown [1]
Regulace
- Both GAD65 and GAD67 are regulated via
- Phosphorylation of a dynamic catalytic loop [2]
- Regulation of these isoforms differs
- Both GAD67 and GAD65 are also regulated post-translationally by Pyridoxal 5’-phosphate (PLP)
- GAD is activated when bound to PLP
- Inactive when not bound to PLP [2]
GAD mRNA expression
- Can be visualised and quantified using in situ hybridisation
GAD 25
- Third form of human GAD
- Present in pancreatic islets, testis, and likely other endocrine organs, including adrenal cortex
- Why GAD25 is expressed in these tissues as well as in rodent embryonic brain remains uncertain [4]
- GAD67 splice variant: GAD25
- GAD25 reactivity in 105 newly-diagnosed children with type 1 diabetes and 74 control subjects
- 14 (13%) of the diabetic subjects were positive for GAD67 autoantibodies
- 3 (3%) were positive for GAD25 reactivity
- None of which were GAD67 antibody-positive
- Autoreactivity to GAD25 is rare in newly diagnosed type 1 diabetes and does not underlie GAD67 reactivity [5]
GAD 44
- Truncated forms of GAD67 are also expressed (GAD25 and GAD44), which are translated from two embryonic-specific splice variants of GAD67 messenger RNA.
- www.sciencedirect.com/science/article/abs/pii/S030645220000275X
GAD65+/- mice
- Have symptoms defined similarly to ADHD in humans [2]
GAD65-/- mice
- Survive with a slightly increased tendency in seizures [2]
GAD65
- Most as inactive apoenzyme
- Can be induced by nerve activity [1]
- Synthesizes GABA for neurotransmission
- Only necessary at nerve terminals and synapses
- Aid in neurotransmission
- Forms a complex with
- Heat Shock Cognate 70 (HSC70)
- Cysteine string protein (CSP)
- Vesicular GABA transporter VGAT
- Helps package GABA into vesicles for release during neurotransmission [2]
- Not transcribed until later in life
- Not needed until slightly later in development when synaptic inhibition is more prevalent [2]
- GAD65 is activated by phosphorylation
- GAD65 is predominantly found inactivated (~72%) [2]
- GAD65 is phosphorylated, and therefore regulated by, protein kinase C (PKC)
- GAD65 binds PLP when GABA is needed for neurotransmission [2]
- GAD65 is dominant in the visual and neuroendocrine systems, which undergo more phasic changes [2]
- GAD65, an autoantigen in type I diabetes, is transiently activated in response to the demand for extra GABA in neurotransmission [3]
- Anchored to synaptic vesicles
- Mediates transient GABA synthesis in response to acute demand and facilitates the transport of GABA-containing synaptic vesicles
- From the Golgi apparatus to the synaptic terminals [2]
GAD67-/- mice
- Born with cleft palate
- Die within a day after birth [2]
GAD67
- Most is present as a pyridoxal phosphate-bound permanently active holoenzyme [1]
- Spread evenly throughout the cell while [2]
- Synthesizes GABA for neuron activity unrelated to neurotransmission
- Synaptogenesis
- Protection from neural injury
- Requires widespread, ubiquitous presence of GABA
- Transcribed during early development
- Needed throughout development for normal cellular functioning [2]
- GAD67 is inhibited by phosphorylation
- GAD67 is predominantly found activated (~92%) [2]
- GAD67 is phosphorylated at threonine 91 by protein kinase A (PKA)
- Majority of GAD67 is bound to PLP at any given time - aktivní [2]
- Believed that GAD67 is present at higher amounts in tonically active neurons [2]
- GAD67 is present mainly in the cytoplasm of inhibitory neurons and regulates the basal level of GABA [3]
