ACT domains are commonly involved in specifically binding an amino acid or other small ligand leading to regulation of the enzyme; Members of this CD belong to the superfamily of ACT regulatory domains. Pairs of ACT domains are commonly involved in specifically binding an amino acid or other small ligand leading to regulation of the enzyme. The ACT domain has been detected in a number of diverse proteins; some of these proteins are involved in amino acid and purine biosynthesis, phenylalanine hydroxylation, regulation of bacterial metabolism and transcription, and many remain to be characterized. ACT domain-containing enzymes involved in amino acid and purine synthesis are in many cases allosteric enzymes with complex regulation enforced by the binding of ligands. The ACT domain is commonly involved in the binding of a small regulatory molecule, such as the amino acids L-Ser and L-Phe in the case of D-3-phosphoglycerate dehydrogenase and the bifunctional chorismate mutase-prephenate dehydratase enzyme (P-protein), respectively. Aspartokinases typically consist of two C-terminal ACT domains in a tandem repeat, but the second ACT domain is inserted within the first, resulting in, what is normally the terminal beta strand of ACT2, formed from a region N-terminal of ACT1. ACT domain repeats have been shown to have nonequivalent ligand-binding sites with complex regulatory patterns such as those seen in the bifunctional enzyme, aspartokinase-homoserine dehydrogenase (ThrA). In other enzymes, such as phenylalanine hydroxylases, the ACT domain appears to function as a flexible small module providing allosteric regulation via transmission of conformational changes, these conformational changes are not necessarily initiated by regulatory ligand binding at the ACT domain itself. ACT domains are present either singularly, N- or C-terminal, or in pairs present C-terminal or between two catalytic domains. Unique to cyanobacteria are four ACT domains C-terminal to an aspartokinase domain. A few proteins are composed almost entirely of ACT domain repeats as seen in the four ACT domain protein, the ACR protein, found in higher plants; and the two ACT domain protein, the glycine cleavage system transcriptional repressor (GcvR) protein, found in some bacteria. Also seen are single ACT domain proteins similar to the Streptococcus pneumoniae ACT domain protein (uncharacterized pdb structure 1ZPV) found in both bacteria and archaea. Purportedly, the ACT domain is an evolutionarily mobile ligand binding regulatory module that has been fused to different enzymes at various times.

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gi 1063706340  84 VFSGKNQPGMLVSVLEAFEDIGLNV--LEARAS 114
Cdd:cd04880     3 VFSLKNKPGALAKALKVFAERGINLtkIESRPS 35

ACT domain of the nonheme iron-dependent, aromatic amino acid hydroxylases (AAAH); ACT domain of the nonheme iron-dependent, aromatic amino acid hydroxylases (AAAH): Phenylalanine hydroxylases (PAH), tyrosine hydroxylases (TH) and tryptophan hydroxylases (TPH), both peripheral (TPH1) and neuronal (TPH2) enzymes. This family of enzymes shares a common catalytic mechanism, in which dioxygen is used by an active site containing a single, reduced iron atom to hydroxylate an unactivated aromatic substrate, concomitant with a two-electron oxidation of tetrahydropterin (BH4) cofactor to its quinonoid dihydropterin form. Eukaryotic AAAHs have an N-terminal ACT (regulatory) domain, a middle catalytic domain and a C-terminal domain which is responsible for the oligomeric state of the enzyme forming a domain-swapped tetrameric coiled-coil. The PAH, TH, and TPH enzymes contain highly conserved catalytic domains but distinct N-terminal ACT domains and differ in their mechanisms of regulation. One commonality is that all three eukaryotic enzymes appear to be regulated, in part, by the phosphorylation of serine residues N-terminal of the ACT domain. Also included in this CD are the C-terminal ACT domains of the bifunctional chorismate mutase-prephenate dehydratase (CM-PDT) enzyme and the prephenate dehydratase (PDT) enzyme found in plants, fungi, bacteria, and archaea. The P-protein of Escherichia coli (CM-PDT) catalyzes the conversion of chorismate to prephenate and then the decarboxylation and dehydration to form phenylpyruvate. These are the first two steps in the biosynthesis of L-Phe and L-Tyr via the shikimate pathway in microorganisms and plants. The E. coli P-protein (CM-PDT) has three domains with an N-terminal domain with chorismate mutase activity, a middle domain with prephenate dehydratase activity, and an ACT regulatory C-terminal domain. The prephenate dehydratase enzyme has a PDT and ACT domain. The ACT domain is essential to bring about the negative allosteric regulation by L-Phe binding. L-Phe binds with positive cooperativity; with this binding, there is a shift in the protein to less active tetrameric and higher oligomeric forms from a more active dimeric form. Members of this CD belong to the superfamily of ACT regulatory domains.

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gi 1063706340  84 VFSGKNQPGMLVSVLEAFEDIGLNV--LEARAS 114
Cdd:cd04880     3 VFSLKNKPGALAKALKVFAERGINLtkIESRPS 35

ACT domain of the nonheme iron-dependent, aromatic amino acid hydroxylases (AAAH); ACT domain of the nonheme iron-dependent, aromatic amino acid hydroxylases (AAAH): Phenylalanine hydroxylases (PAH), tyrosine hydroxylases (TH) and tryptophan hydroxylases (TPH), both peripheral (TPH1) and neuronal (TPH2) enzymes. This family of enzymes shares a common catalytic mechanism, in which dioxygen is used by an active site containing a single, reduced iron atom to hydroxylate an unactivated aromatic substrate, concomitant with a two-electron oxidation of tetrahydropterin (BH4) cofactor to its quinonoid dihydropterin form. Eukaryotic AAAHs have an N-terminal ACT (regulatory) domain, a middle catalytic domain and a C-terminal domain which is responsible for the oligomeric state of the enzyme forming a domain-swapped tetrameric coiled-coil. The PAH, TH, and TPH enzymes contain highly conserved catalytic domains but distinct N-terminal ACT domains and differ in their mechanisms of regulation. One commonality is that all three eukaryotic enzymes appear to be regulated, in part, by the phosphorylation of serine residues N-terminal of the ACT domain. Also included in this CD are the C-terminal ACT domains of the bifunctional chorismate mutase-prephenate dehydratase (CM-PDT) enzyme and the prephenate dehydratase (PDT) enzyme found in plants, fungi, bacteria, and archaea. The P-protein of Escherichia coli (CM-PDT) catalyzes the conversion of chorismate to prephenate and then the decarboxylation and dehydration to form phenylpyruvate. These are the first two steps in the biosynthesis of L-Phe and L-Tyr via the shikimate pathway in microorganisms and plants. The E. coli P-protein (CM-PDT) has three domains with an N-terminal domain with chorismate mutase activity, a middle domain with prephenate dehydratase activity, and an ACT regulatory C-terminal domain. The prephenate dehydratase enzyme has a PDT and ACT domain. The ACT domain is essential to bring about the negative allosteric regulation by L-Phe binding. L-Phe binds with positive cooperativity; with this binding, there is a shift in the protein to less active tetrameric and higher oligomeric forms from a more active dimeric form. Members of this CD belong to the superfamily of ACT regulatory domains.

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gi 1063706340  84 VFSGKNQPGMLVSVLEAFEDIGLNV--LEARAS 114
Cdd:cd04880     3 VFSLKNKPGALAKALKVFAERGINLtkIESRPS 35

basic helix-loop-helix (bHLH) domain found in Arabidopsis thaliana genes coding transcription factors and similar proteins; bHLH proteins are the second largest class of plant transcription factors that regulate transcription of genes that are involve in many essential physiological and developmental process. bHLH proteins are transcriptional regulators that are found in organisms from yeast to humans. The Arabidopsis bHLH proteins that have been characterized so far have roles in regulation of fruit dehiscence, cell development (carpel, anther and epidermal), phytochrome signaling, flavonoid biosynthesis, hormone signaling and stress responses.

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gi 1063706340   1 MVSREQKRGSLQEKFQLLRSITNSHAENDT-SIIMDASKYIQKLKQKVE 48
Cdd:cd11393     2 SIAERKRREKINERIRALRSLVPNGGKTDKaSILDEAIEYIKFLQEQVK 50

C-terminal ACT domain of the bifunctional chorismate mutase-prephenate dehydratase (CM-PDT) enzyme and the prephenate dehydratase (PDT) enzyme; The C-terminal ACT domain of the bifunctional chorismate mutase-prephenate dehydratase (CM-PDT) enzyme and the prephenate dehydratase (PDT) enzyme, found in plants, fungi, bacteria, and archaea. The P-protein of E. coli (CM-PDT, PheA) catalyzes the conversion of chorismate to prephenate and then the decarboxylation and dehydration to form phenylpyruvate. These are the first two steps in the biosynthesis of L-Phe and L-Tyr via the shikimate pathway in microorganisms and plants. The E. coli P-protein (CM-PDT) has three domains with an N-terminal domain with chorismate mutase activity, a middle domain with prephenate dehydratase activity, and an ACT regulatory C-terminal domain. The prephenate dehydratase enzyme has a PDT and ACT domain. The ACT domain is essential to bring about the negative allosteric regulation by L-Phe binding. L-Phe binds with positive cooperativity; with this binding, there is a shift in the protein to less active tetrameric and higher oligomeric forms from a more active dimeric form. Members of this CD belong to the superfamily of ACT regulatory domains.

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gi 1063706340  84 VFSGKNQPGMLVSVLEAFEDIGLNV--LEAR 112
Cdd:cd04905     5 VFTLPNKPGALYDVLGVFAERGINLtkIESR 35