Kinase Family GAPDH

Gerard — Thu, 10 May 2012 14:34:54 GMT

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	The glycolytic enzyme, Glyceraldehyde-3-phosphate dehydrogenase has been demonstrated to have a kinase activity towards viral proteins, a GABA receptor, and in vitro.		The glycolytic enzyme, Glyceraldehyde-3-phosphate dehydrogenase has been demonstrated to have a kinase activity towards viral proteins, a GABA receptor, and in vitro.
		+
		+	====GAPDH and Glycolysis====
		+	GAPDH has a kinase function during glycolysis: it first oxidizes glyceraldehyde 3-phosphate, converting the aldehyde group to a carboxylic acid, and then adds inorganic phosphate to the alcohol group of that carboxylic acid ([http://en.wikipedia.org/wiki/Glyceraldehyde_3-phosphate_dehydrogenase Wikipedia]). GAPDH uses the energy from the first reaction to drive the unusual, and energetically unfavorable, phosphorylation with orthophosphate (Pi). The next step in glycolysis inovlves phosphoglycerate kinase (PGK) acting as a form of phosphatase or reverse kinase: it removes one of the phosphates on the glyceraldehyde diphosphate by converting ADP to ATP.

	====Evidence for Protein Kinase Activity====		====Evidence for Protein Kinase Activity====
-	GAPDH from rabbit muscle was reported to ~~autophorphorylate~~ and transphosphorylate two uncharacterized proteins <cite>Kawamoto</cite>. Transphosphorylation appeared to involve transfer of the phosphate originally used to autophosphorylate, using ATP as a donor. The pH lability profile of the autophosphorylated form suggested the presence of an acyl phosphate (probably phosphorylation of carboxylic acid) rather than the typical ester phosphates of Ser/Thr/Tyr phosphorylation.	+	GAPDH from rabbit muscle was reported to autophosphorylate and transphosphorylate two uncharacterized proteins <cite>Kawamoto</cite>. Transphosphorylation appeared to involve transfer of the phosphate originally used to autophosphorylate, using ATP as a donor. The pH lability profile of the autophosphorylated form suggested the presence of an acyl phosphate (probably phosphorylation of carboxylic acid) rather than the typical ester phosphates of Ser/Thr/Tyr phosphorylation.
-		+
-	GAPDH has a kinase function during glycolysis: it first oxidizes glyceraldehyde 3-phosphate, converting the aldehyde group to a carboxylic acid, and then adds inorganic phosphate to the alcohol group of that carboxylic acid ([http://en.wikipedia.org/wiki/Glyceraldehyde_3-phosphate_dehydrogenase Wikipedia]). GAPDH uses the energy from the first reaction to drive the unusual, and energetically unfavorable, phosphorylation with inorganic phosphate. The next step in glycolysis inovlves phosphoglycerate kinase acting as a form of phosphatase or reverse kinase: it removes one of the phosphates on the glyceraldehyde diphosphate by converting ADP to ATP.	+
-		+
-	~~HBV: <cite>Duclos-Vallee</cite>~~	+
-	~~GABAa: <cite>Laschet</cite>~~	+

		+	GAPDH has been reported to phosphorylate GABRA1, a subunit of the receptor for the inhibitory neurotransmitter GABA <cite>Laschet</cite>. GAPDH binds tightly to GABRA1, and phosphorylates it on T337 and S416, both residues found within a conserved Nxxx[S/T]K motif. Labeling experiments suggest that GAPDH and PGK produce ATP while anchored at the receptor, and that GAPDH uses this ATP to autophosphorylate and transphosphorylate the receptor. This system may have evolved from one where glycolytic enzymes are localized to the membrane to produce ATP to power ATPase-driven ion channels <cite>Silver, Wu</cite>, and suggests that the phosphorylation may be regulatory and may respond to levels of ATP/ADP/Pi, Mg++ or glycolytic precursors. A separate study <cite>Wu</cite> also reports GAPDH autophosphorylation at the neuronal post-synaptic density, and that autophosphorylated GAPDH had an increased affinity for binding actin.

-	~~A second role for mammalian~~ GAPDH in phos- phate group transfer was recently described by Engel et al. [39]. Their studies examined the structure and function of a gene family, termed nm23, which ex- hibited potential metastasis suppressor activity. However, the function of the gene product responsi- ble for this activity was unknown. Although it had been ~~established that~~ the nm23 tumor suppresser gene encoded a nucleoside diphosphate kinase activ- ity, it did not appear that such an activity was re- sponsible for its tumor suppressor action. An alter- native function was described for the nm23 protein ~~as a serine/threonine speci¢c phosphotransferase. Cu~~- riously, the highly puri¢ed nm23 protein did not ex- hibit this activity. Subsequently, in human cells, it was determined that it existed in a protein complex with a 37 kDa protein. The latter was identi¢ed as GAPDH by sequence analysis. Stoichiometric exami- nation suggested a 1:1 ratio and a molecular mass of 107.4 kDa, indicating a GAPDH dimer/nm23 dimer interaction. Of note, GAPDH glycolytic activity and diphosphate kinase activity were not inhibited by formation of this complex. Further, no reduction of phosphotransferase activity was observed in the pres- ence of 80 M NADH.	+	GAPDH has also been reported to phosphorylate the core protein of hepatitis B virus <cite>Duclos-Vallee</cite>.

		+	====Other Functions====
		+	GAPDH has also been reported to activate transcription, as part of the OCA-S complex, along with lactate dehydrogenase <cite>Zheng</cite>; may link NO signaling to apoptosis <cite>Hara</cite>; and be involved in ER-to-Golgi transport <cite>Tisdale</cite>

-	~~GADPH~~ is also the substrate or binding partner of typical protein kinases, including PKC, CAMK2 and EGFR, Src~~...~~	+	GAPDH is also the substrate or binding partner of typical protein kinases, including PKC, CAMK2 and EGFR, Src, and has been reported to be tightly bound to nucleoside diphosphate kinases (NDK)

	====Domain Structure====		====Domain Structure====
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	====References====		====References====
	<biblio>		<biblio>
		+	#Hara pmid=16505364
	#Kawamoto pmid=3955021		#Kawamoto pmid=3955021
	#Laschet pmid=15342727		#Laschet pmid=15342727
		+	#Tisdale pmid=17488287
		+	#Wu pmid=9371836
		+	#Zheng pmid=12887926
	</biblio>		</biblio>

	====Unlinked References====		====Unlinked References====
	#Duclos-Vallee pmid=9680129		#Duclos-Vallee pmid=9680129
		+	#Silver pmid=9145812

Kinase Family BRD

Gerard — Thu, 10 May 2012 13:11:07 GMT

← Older revision		Revision as of 13:11, 10 May 2012
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	====Evolution====		====Evolution====
-	Mammals have four BRDs (BRD2/RING3, BRD3, BRD4 and BRDT), Drosophila has one (fs(1)h) and C. elegans has 3. A more distantly related homolog is found in fungi (S. cerevisiae Bdf1 and homologs) ~~but~~ that ~~may~~ not ~~be truly~~ orthologous~~, as others have reported that~~ to ~~be a homolog of Taf1. Other~~ BRD ~~proteins are found across many eukaryotes~~.	+	Mammals have four BRDs (BRD2/RING3, BRD3, BRD4 and BRDT), Drosophila has one (fs(1)h) and C. elegans has 3. A more distantly related homolog is found in fungi (S. cerevisiae Bdf1 and homologs) and in plants. Other basal lineages have proteins with single bromodomains that are not clearly orthologous to BRD, but may have related functions.

	====Evidence for Protein Kinase Activity====		====Evidence for Protein Kinase Activity====
-	Human BRD2 was first identified as an autophosphorylating nuclear-specific protein in Hela extracts <cite>Denis</cite>. Recombinant BRD2 expressed in ''E. coli'' showed in vitro kinase activity. However, the kinase activity was only seen when the purified recombinant protein was first incubated with Hela cell extract and repurified. It was suggested that this incubation could allow BRD2 to be activated by phosphorylation, but it is also possible that this step allowed BRD2 to bind to a human kinase which was then responsible for the observed activity. Recombinant BRD2 purified from COS cells also showed in vitro kinase activity, without pre-incubation.	+	Human BRD2 was first identified as an autophosphorylating nuclear-specific protein in Hela extracts <cite>Denis</cite>. Recombinant BRD2 expressed in ''E. coli'' showed in vitro kinase activity. However, the kinase activity was only seen when the purified recombinant protein was first incubated with Hela cell extract and repurified. It was suggested that this incubation could allow BRD2 to be activated by phosphorylation, but it is also possible that this step allowed BRD2 to bind to a human kinase which was then responsible for the observed activity. Recombinant BRD2 purified from COS cells also showed in vitro kinase activity, without pre-incubation. Mutation of a C-terminal lysine (K578A) abolished the activity seen in ''E. coli'', implicating it either in cryptic kinase activity or binding to an active human kinase.

-	If the BRD kinase activity is due to a tightly bound kinase, the most likely candidate is CDK9. It is not known if BRD2 binds CDK9, but BRD4, BRDT and the Drosophila homolog, fs(1)h are all reported to bind CDK9, and BRD4 may induce CDK9 phosphorylation <cite>Zhou, Bisgrove</cite>.	+	If the BRD kinase activity is due to a tightly bound kinase, the most likely candidate is CDK9. It is not known if BRD2 binds CDK9, but BRD4, BRDT and the Drosophila homolog, fs(1)h are all reported to bind CDK9, and BRD4 may induce CDK9 phosphorylation <cite>Zhou, Bisgrove</cite>. Bdf1, the yeast BRD is also known to bind to CK2 kinase <cite>Sawa</cite>.

-	~~BRD contain two bromodomains and~~ a ~~novel conserved C~~-terminal ~~region~~, ~~as well as less~~-~~conserved regions~~. ~~None show an obvious similarity to any known kinases. Mutation~~ of a ~~C-terminal lysine (K578A) abolished the~~ activity seen in ''E. coli'', ~~implicating it either~~ in ~~cryptic~~ kinase ~~activity or binding~~ to ~~an active human kinase~~.	+	Human BRD4 has also been shown to be a kinase with autophosphorylation and transphosphorylation activity <cite>Devaiah</cite>. Deletion mutations mapped the kinase activity to the N-terminal half, from AA 1-699. Deletion of either bromodomain with this region caused a partial loss of activity, and deletion of both bromodomains caused greater but incomplete loss of activity. Kinase activity was seen in protein purified from E. coli or from insect Sf9 cells, and survived an in-gel kinase assay after denaturation and renaturation. BRD4 phosphorylated Ser2 of the RNA polymerase C-terminal domain, with a pH profile that was distinct from other Ser2 kinases, and which was insensitive to CDK inhibitors.

	====References====		====References====
	<biblio>		<biblio>
	#Bisgrove pmid=17690245		#Bisgrove pmid=17690245
		+	#Devaiah pmid=22509028
	#Zhou pmid=18971272		#Zhou pmid=18971272
	#Denis pmid=8595877		#Denis pmid=8595877
		+	#Sawa pmid=15143168
	</biblio>		</biblio>

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Kinase Family GAPDH

Kinase Family BRD