N-terminal ACT domain of the Escherichia coli IlvH-like regulatory subunit of acetohydroxyacid synthase (AHAS); ACT_AHAS: N-terminal ACT domain of the Escherichia coli IlvH-like regulatory subunit of acetohydroxyacid synthase (AHAS). AHAS catalyses the first common step in the biosynthesis of the three branched-chain amino acids. The first step involves the condensation of either pyruvate or 2-ketobutyrate with the two-carbon hydroxyethyl fragment derived from another pyruvate molecule, covalently bound to the coenzyme thiamine diphosphate. Bacterial AHASs generally consist of regulatory and catalytic subunits. The effector (valine) binding sites are proposed to be located in two symmetrically related positions in the interface between a pair of N-terminal ACT domains with the C-terminal domain of IlvH contacting the catalytic dimer. Plants Arabidopsis and Oryza have tandem IlvH subunits; both the first and second ACT domain sequences are present in this CD. Members of this CD belong to the superfamily of ACT regulatory domains.

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               ....*....|....*....|....*....|....*....|....*....|....*....|....*....|.
gi 24115014 10 ILELTVRNHPGVMTHVCGLFARRAFNVEGILCLPIQDSDKSHIWLLVN-DDQRLEQMISQIAKLEDVVKVQ 79
Cdd:cd04878  2 TLSVLVENEPGVLNRISGLFARRGFNIESLTVGPTEDPGISRITIVVEgDDDVIEQIVKQLNKLVDVLKVS 72

acetolactate synthase, small subunit; Acetolactate synthase is a heterodimeric thiamine pyrophosphate enzyme with large and small subunits. One of the three isozymes in E. coli K12 contains a frameshift in the large subunit gene and is not expressed. acetohydroxyacid synthase is a synonym. [Amino acid biosynthesis, Pyruvate family]

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                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|.
gi 24115014    10 ILELTVRNHPGVMTHVCGLFARRAFNVEGILCLPIQDSDKSHIWLLVN-DDQRLEQMISQIAKLEDVVKVQ 79
Cdd:TIGR00119   3 ILSVLVENEPGVLSRVAGLFTRRGFNIESLTVGPTEDPDLSRMTIVVVgDDKVLEQITKQLNKLVDVIKVS 73

N-terminal ACT domain of the Escherichia coli IlvH-like regulatory subunit of acetohydroxyacid synthase (AHAS); ACT_AHAS: N-terminal ACT domain of the Escherichia coli IlvH-like regulatory subunit of acetohydroxyacid synthase (AHAS). AHAS catalyses the first common step in the biosynthesis of the three branched-chain amino acids. The first step involves the condensation of either pyruvate or 2-ketobutyrate with the two-carbon hydroxyethyl fragment derived from another pyruvate molecule, covalently bound to the coenzyme thiamine diphosphate. Bacterial AHASs generally consist of regulatory and catalytic subunits. The effector (valine) binding sites are proposed to be located in two symmetrically related positions in the interface between a pair of N-terminal ACT domains with the C-terminal domain of IlvH contacting the catalytic dimer. Plants Arabidopsis and Oryza have tandem IlvH subunits; both the first and second ACT domain sequences are present in this CD. Members of this CD belong to the superfamily of ACT regulatory domains.

                       10        20        30        40        50        60        70
               ....*....|....*....|....*....|....*....|....*....|....*....|....*....|.
gi 24115014 10 ILELTVRNHPGVMTHVCGLFARRAFNVEGILCLPIQDSDKSHIWLLVN-DDQRLEQMISQIAKLEDVVKVQ 79
Cdd:cd04878  2 TLSVLVENEPGVLNRISGLFARRGFNIESLTVGPTEDPGISRITIVVEgDDDVIEQIVKQLNKLVDVLKVS 72

acetolactate synthase 3 regulatory subunit; Reviewed

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|.
gi 24115014   10 ILELTVRNHPGVMTHVCGLFARRAFNVEGILCLPIQDSDKSHIWLLVN-DDQRLEQMISQIAKLEDVVKVQ 79
Cdd:PRK11895   4 TLSVLVENEPGVLSRVAGLFSRRGYNIESLTVGPTEDPGLSRMTIVTSgDEQVIEQITKQLNKLIDVLKVV 74

acetohydroxyacid synthase small subunit

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                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 24115014   11 LELTVRNHPGVMTHVCGLFARRAFNVEGILCLPIQDSDKSHIWLLV-NDDQRLEQMISQIAKLEDVVKVQ 79
Cdd:CHL00100   5 LSVLVEDESGVLTRIAGLFARRGFNIESLAVGPAEQKGISRITMVVpGDDRTIEQLTKQLYKLVNILKVQ 74

ACT domain; ACT domains bind to amino acids and regulate associated enzyme domains. These ACT domains are found at the C-terminus of the RelA protein.

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                 ....*....|....*....|....*....|....*....|....*....|....*....|
gi 24115014   19 PGVMTHVCGLFARRAFNVEGILCLPIQDSDKSHIWLLVNDDQRLEQMISQIAKLEDVVKV 78
Cdd:pfam13710  3 PGVLERVLRVVRRRGFHVTSMNMSATEDGGLVRIQLTVESDRSVELLLNQLEKLYDVVKV 62

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 24115014 11 LELTVRNHPGVMTHVCGLFARRAFNVEGILCLPIQDSDKSHIWLLVNDDQRLEQMISQI 69
Cdd:cd02116  1 LTVSGPDRPGLLAKVLSVLAEAGINITSIEQRTSGDGGEADIFIVVDGDGDLEKLLEAL 59