Literature summary for 2.3.2.13 extracted from

Katt, W.P.; Antonyak, M.A.; Cerione, R.A.
Opening up about tissue transglutaminase when conformation matters more than enzymatic activity (2018), Med One, 3, e180011 .

Activating Compound

Activating Compound	Comment	Organism
GDP	GTP/GDP and Ca2+ are able to compete with one another to convert tTG from the closed- to open-state, and vice versa	Homo sapiens
GTP	GTP/GDP and Ca2+ are able to compete with one another to convert tTG from the closed- to open-state, and vice versa	Homo sapiens
additional information	Arg580 in wild-type tTG forms several hydrogen bonds with GDP, while Arg478 binds only to the terminal phosphate. Arg476 binds more poorly to the terminal phosphate of GDP, and Ser171 does not form hydrogen bonds with the GDP molecule	Homo sapiens
thioredoxin-1	thioredoxin-1 is released by macrophages exposed to inflammatory stimuli in sufficient quantity to reduce the tTG C370-C371 disulfide bond, activating the enzyme	Homo sapiens

Application

Application	Comment	Organism
diagnostics	tTG is considered a prognostic marker for Parkinson's disease. tTG antibodies, and crosslinked gliadin, act as diagnostic tools in celiac disease	Homo sapiens

Cloned(Commentary)

Cloned (Comment)	Organism
recombinant expression of enzyme mutants in HeLa cells and in NIH 3T3 fibroblasts, nearly half of the cells die within 24 h. In contrast, introduction of wild-type tTG into those same cells does not induce cell death. Mutant R580L/C277A still induces cell death. Although ectopic expression of tTG mutant R580A in striatal cells is not sufficient to induce cell death, it does so in HeLa or NIH 3T3 cells	Homo sapiens

Cloned (Comment)

Organism

recombinant expression of enzyme mutants in HeLa cells and in NIH 3T3 fibroblasts, nearly half of the cells die within 24 h. In contrast, introduction of wild-type tTG into those same cells does not induce cell death. Mutant R580L/C277A still induces cell death. Although ectopic expression of tTG mutant R580A in striatal cells is not sufficient to induce cell death, it does so in HeLa or NIH 3T3 cells

Homo sapiens

Protein Variants

Protein Variants	Comment	Organism
C277A	the mutant is unable to bind guanine nucleotides	Homo sapiens
C277S	the mutation has no effect on cell death	Homo sapiens
C277V	the mutant is susceptible to digestion by trypsin, and significantly impaired in nucleotide binding	Homo sapiens
D306N/N310A	the purified tTG mutant adopts a conformation similar to that of wild-type tTG, based on their mutual ability to bind bodipy-GTP-gammaS and to resist proteolysis by trypsin	Homo sapiens
D434A	the mutant can be transiently expressed in NIH 3T3 cells but not be generated as recombinant protein. The mutant is cytotoxic when expressed in NIH 3T3 cells	Homo sapiens
F174A	the F174A mutant is deficient in nucleotide binding, and is digested by trypsin in the presence of GTP-gammaS, Phe174 appears to be involved in a pi-stacking interaction	Homo sapiens
F174W	mutant resists proteolysis and is able to bind nucleotide	Homo sapiens
K677A	the mutant can be transiently expressed in NIH 3T3 cells but not be generated as recombinant protein, the mutant is unable to bind bodipy-GTP-gammaS, and shows high sensitivity to degradation by trypsin. The mutant is cytotoxic when expressed in NIH 3T3 cells	Homo sapiens
additional information	identification of tTG mutants which adopt either the open or the closed state, overview	Homo sapiens
N681A	the mutant can be transiently expressed in NIH 3T3 cells and generated as recombinant protein. The mutant is cytotoxic when expressed in NIH 3T3 cells	Homo sapiens
Q163D	the mutant shows no loss of nucleotide binding ability when assayed with [alpha-32P] GTP, and exhibits only a moderate loss of binding ability when assayed with [35S]GTP-gammaS	Homo sapiens
Q163L	the mutant shows no loss of nucleotide binding ability when assayed with [alpha-32P] GTP, and exhibits only a moderate loss of binding ability when assayed with [35S]GTP-gammaS	Homo sapiens
Q164L	the mutant shows no loss of nucleotide binding ability when assayed with [alpha-32P] GTP, and exhibits only a moderate loss of binding ability when assayed with [35S]GTP-gammaS	Homo sapiens
Q169L	the mutant shows no loss of nucleotide binding ability when assayed with [alpha-32P] GTP, and exhibits only a moderate loss of binding ability when assayed with [35S]GTP-gammaS	Homo sapiens
R476A	the mutant binds nucleotide as well as the wild-type enzyme	Homo sapiens
R478A	the mutant has partially reduced nucleotide binding	Homo sapiens
R579A	the R579A mutant of tTG is far more susceptible to proteolysis by trypsin or by calpain than the wild-type	Homo sapiens
R580A	the mutant is GTP-binding deficient	Homo sapiens
R580K	decreases in nucleotide binding are observed for the R580L and R580K mutants	Homo sapiens
R580L	decreases in nucleotide binding are observed for the R580L and R580K mutants	Homo sapiens
R580L/C277A	the tTG mutant is deficient in GTP-binding and protein crosslinking activity, but still induces cell death	Homo sapiens
S171A	the mutant binds nucleotide as well as the wild-type enzyme	Homo sapiens
W254A	the mutant can be transiently expressed in NIH 3T3 cells and generated as recombinant protein, the mutant is unable to bind bodipy-GTP-gammaS, and shows high sensitivity to degradation by trypsin. W254A forms a dimer of tTG molecules in the open-state conformation. The mutant is cytotoxic when expressed in NIH 3T3 cells	Homo sapiens
Y516C	the mutant is less capable of binding guanine nucleotide compared to wild-type	Homo sapiens
Y516F	the mutant is less capable of binding guanine nucleotide compared to wild-type	Homo sapiens

Inhibitors

Inhibitors	Comment	Organism	Structure
KCC009	a specific tTG inhibitor	Homo sapiens

Localization

Localization	Comment	Organism	GeneOntology No.	Textmining
cell surface	-	Homo sapiens	9986	-
endoplasmic reticulum	tTG and alpha-synuclein both localize to the endoplasmic reticulum in disease brain samples	Homo sapiens	5783	-
extracellular	-	Homo sapiens	-	-
intracellular	-	Homo sapiens	5622	-

Metals/Ions

Metals/Ions	Comment	Organism	Structure
Ca2+	required, three calcium binding sites are thought to exist on tTG, GTP/GDP and Ca2+ are able to compete with one another to convert tTG from the closed- to open-state, and vice versa	Homo sapiens

Natural Substrates/ Products (Substrates)

Natural Substrates	Organism	Comment (Nat. Sub.)	Natural Products	Comment (Nat. Pro.)	Rev.
alpha-synuclein glutamine + alkylamine	Homo sapiens	-	alpha-synuclein N5-alkylglutamine + NH3	-	?
ApoE glutamine + alkylamine	Homo sapiens	-	ApoE N5-alkylglutamine + NH3	-	?
gliadin glutamine + alkylamine	Homo sapiens	-	gliadin N5-alkylglutamine + NH3	-	?
protein glutamine + alkylamine	Homo sapiens	-	protein N5-alkylglutamine + NH3	-	?

Organism

Organism	UniProt	Comment	Textmining
Homo sapiens	P21980	-	-

Source Tissue

Source Tissue	Comment	Organism	Textmining
brain	-	Homo sapiens	-
Caco-2 cell	Caco-2 intestinal cancer cells express crosslinking-competent tTG on their surface	Homo sapiens	-
central nervous system	the central nervous system has a tTG splice variant which is termed tTG-short, or tTG-S. tTG-S adopts a conformation similar to the open-state	Homo sapiens	-
intestine	-	Homo sapiens	-
neuroblastoma cell	-	Homo sapiens	-
pancreatic cancer cell	-	Homo sapiens	-
SH-SY5Y cell	-	Homo sapiens	-

Substrates and Products (Substrate)

Substrates	Comment Substrates	Organism	Products	Comment (Products)	Rev.
alpha-synuclein glutamine + alkylamine	-	Homo sapiens	alpha-synuclein N5-alkylglutamine + NH3	-	?
ApoE glutamine + alkylamine	-	Homo sapiens	ApoE N5-alkylglutamine + NH3	-	?
gliadin glutamine + alkylamine	-	Homo sapiens	gliadin N5-alkylglutamine + NH3	-	?
protein glutamine + alkylamine	-	Homo sapiens	protein N5-alkylglutamine + NH3	-	?

Synonyms

Synonyms	Comment	Organism
Galphah	-	Homo sapiens
TG2	-	Homo sapiens
tissue transglutaminase	-	Homo sapiens
transglutaminase	-	Homo sapiens
tTG	-	Homo sapiens
type 2 transglutaminase	-	Homo sapiens

General Information

General Information	Comment	Organism
malfunction	specific tTG inhibitors, such as KCC009, can block alpha-synuclein aggregation in SH-SY5Y neuroblastoma cells	Homo sapiens
additional information	intracellular tTG is predominantly in the closed-state, with a small portion being in the crosslinking-competent open-state, while extracellular tTG would adopt the open-state, and be crosslinking-competent. This view is somewhat complicated by the mildly oxidative conditions in the extracellular space. A triad of cysteine residues (Cys 230, Cys 370, and Cys 371) are able to make one of two disulfide bonds (C370-C230, or C370-C371) in oxidative conditions. Either disulfide bond reduces crosslinking catalytic activity, but oxidized tTG maintains a conformation similar to the open-state. Cp4d is a reversible small molecule which has little effect on tTG conformation, while NC9 is a bulkier, irreversible peptidomimetic compound presumed to stabilize tTG in the open-state. Cp4d treatment has little effect on the sensitivity of the assorted cells to glucose-oxygen deprivation-induced cell death. NC9 causes the tTG wild-type and tTG C277S mutant expressing cells to undergo a greater degree of cell death under the same conditions. The conformation of tTG is responsible for the cell death enhancement. Binding partners of tTG depend upon its conformation, confromation-independent binding modes of tTG, structure-function analysis, detailed overview	Homo sapiens
physiological function	type 2 transglutaminase, tTG, is an important player in numerous diseases, including celiac disease, neuronal degenerative diseases, and cancer, and its roles in these diseases often depend as much upon its conformation as its catalytic activity. Several roles of tTG in diseases, detailed overview. ApoE is able to protect against Abeta plaque formation by transporting Abeta out of the brain. Crosslinking by tTG inactivates the protein, rendering it unable to clear Abeta. Parkinson's disease is a related disorder, and tTG plays similar, but unique, roles in this disease as well. Where Alzheimer's disease is driven in part by a buildup of Abeta aggregates, Parkinson's disease is caused by the aggregation of alpha-synuclein. In Parkinson's disease, alpha-synuclein is incorrectly processed into beta-pleated fibrils, which in turn aggregate to form cytoplasmic inclusions called Lewy Bodies. tTG catalyzes the crosslinking of alpha-synuclein, both in vitro and in cell models, tTG and alpha-synuclein both localize to the endoplasmic reticulum in disease brain samples. tTG is the major autoantigen in celiac disease. Celiac disease is an auto-immune disorder in which T-cells attack and damage the small intestine. This process is driven by gliadin, a protein in most grains, which precipitates an immune response. Crosslinking of gliadin formed antigenic complexes. And thioredoxin-1 is released by macrophages exposed to inflammatory stimuli in sufficient quantity to reduce the tTG C370-C371 disulfide bond, activating the enzyme. Since inflammatory conditions are present in celiac disease gut, this effect essentially creates a self-stimulating loop in which activated tTG leads to inflammation, which then activates more tTG. tTG has been shown to play roles in cancer cell adhesion, migration, and invasion via its interactions with fibronectin. tTG binds to fibronectin, and crosslinks it to various surfaces, allowing cells to adhere. Matrix metalloproteinase can then break these crosslinks, and in combination with tTG crosslinking this allows for cell motility. Similarly, tTG is thought to play a role in vesicle trafficking by helping to dock extracellular vesicles (microvesicles) generated by aggressive cancer cells to fibroblasts, through its ability to bind and crosslink fibronectin on the vesicle surface. This docking event can then be blocked by inhibiting its crosslinking activity. tTG can promote either cell survival or apoptosis, depending upon the physiological context. As a pro-survival protein, the crosslinking-competent, open-state form of tTG has been shown to crosslink pRB (a pro-apoptotic protein), causing it to oligomerize and thus lose its activity. This is analogous to its role in Alzheimer's disease, crosslinking ApoE. Closed-state tTG is able to sequester c-Cbl, and block ubiquitinylation and subsequent degradation of the EGF receptor, thereby also promoting cell growth and survival. Thus, both open- and closed-state can tTG promote survival depending upon the specific conditions. The same is true of its pro-apoptotic functions. In pancreatic cancer cells treated with the calcium ionophore A23187, tTG adopts the crosslinking-active open-state to facilitate release of the apoptosis-inducing factor from mitochondria, promoting cell death. In contrast, ectopically expressed tTG in SH-SY5Y cells, which presumably exists in the closed-state, is found to promote apoptosis following osmotic shock or staurosporine treatment. Cytotoxicity of the open-state of tTG	Homo sapiens