Conserved Protein Domain Family
ACT_AKi-HSDH-ThrA_2

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cd04922: ACT_AKi-HSDH-ThrA_2 
ACT domains of the bifunctional enzyme aspartokinase (AK) - homoserine dehydrogenase (HSDH)
This CD includes the second of two ACT domains of the bifunctional enzyme aspartokinase (AK) - homoserine dehydrogenase (HSDH). The ACT domains are positioned between the N-terminal catalytic domain of AK and the C-terminal HSDH domain found in bacteria (Escherichia coli (EC) ThrA) and higher plants (Zea mays AK-HSDH). AK and HSDH are the first and third enzymes in the biosynthetic pathway of the aspartate family of amino acids. AK catalyzes the phosphorylation of Asp to P-aspartyl phosphate. HSDH catalyzes the NADPH-dependent conversion of Asp 3-semialdehyde to homoserine. HSDH is the first committed reaction in the branch of the pathway that leads to Thr and Met. In E. coli, ThrA is subject to allosteric regulation by the end product L-threonine and the native enzyme is reported to be tetrameric. As with bacteria, plant AK and HSDH are feedback inhibited by pathway end products. Maize AK-HSDH is a Thr-sensitive 180-kD enzyme. Arabidopsis AK-HSDH is an alanine-activated, threonine-sensitive enzyme whose ACT domains were shown to be involved in allosteric activation. Members of this CD belong to the superfamily of ACT regulatory domains.
Statistics
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PSSM-Id: 153194
View PSSM: cd04922
Aligned: 11 rows
Threshold Bit Score: 98.9645
Threshold Setting Gi: 83815685
Created: 17-Apr-2006
Updated: 2-Oct-2020
Structure
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Aligned Rows:
 
putative
Feature 1:putative threonine allosteric regulatory site
Evidence:
  • Comment:potentially involved in the binding of Thr.
  • Comment:Kinetic experiments on Arabidopsis AK-HSDH demonstrated that each regulatory (ACT) domain of the monomers of AK-HSDH contained two nonequivalent threonine binding sites, constituted in part by Gln443 and Gln524.
  • Comment:The interaction of threonine with Gln443 of Arabidopsis AK-HSDH led to inhibition of AK activity and facilitated the binding of a second threonine on Gln524. Interaction of this second threonine with Gln524 led to inhibition of HSDH activity.

Sequence Alignment
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Format: Row Display: Color Bits: Type Selection:
Feature 1                                           #                             
P00561      396 LAIISVVGDGMRTLRGISAKFFAALARANINIVAIAQGSSERSISVVVNNDDATTGVRVTHQMLFN 461  Escherichia coli
3250680     488 CSILAAVGQKMASTPGVSCTLFSALAKANINVRAISQGCSEYNVTVVIKREDSVKALRAVHSRFFL 553  thale cress
YP_205501   396 VAIVTLVGDGMRTSKGVASQFFTSLTEVNVNIIAIAQGSSERAISAVIPEDKVSESIKACHENLFN 461  Vibrio fischeri ES114
P49079      492 CSILATVGLRMASTPGVSATLFDALAKANINVRAIAQGCSEYNITIVLKQEDCVRALRAAHSRFFL 557  maize
AAZ27822    400 LSIVSLVGDGMHHQRGVAAKFFSSLAQARVNVVAIAQDSSERSISVVVEQRKCMDAMKVSHQNFFS 465  Colwellia psychrerythraea 34H
YP_200881   422 ISVLAAVGDGMAGQPGVAARLFESLGRAHVNILAIAQGSSERNISVAIDAAHATKALRAAHAGFWL 487  Xanthomonas oryzae pv. oryzae...
YP_444829   403 CSILAVVGDQMAGTPGVAATFFGALGEASVNVRAVAQGSSERNISAVVDRDDARRALRAAHAGFYL 468  Salinibacter ruber DSM 13855
NP_662905   396 LAMVAVVGNKMLGHPGVSAQLFETLGKNGVNVIAVAQGANEMNISLVIDSADENKALNCVHESFFL 461  Chlorobium tepidum TLS
ZP_01120767 392 LAIIALVGDQMKQHQGLSGKMFSALGRNNVNIRAIAQGASERNISAVIRSGDVKKALNTLHEAFFE 457  Robiginitalea biformata HTCC2501
ZP_01448773 396 LSIVTLVGDGMKQSHGTAAKFFQALAQARINNIAIAQGSSERSISTVIEAGKAKKAIKVVHQNFFS 461  alpha proteobacterium HTCC2255
YP_630499   397 LAVLSIVGDGMRHRVGVAGTFFSALADVGCSIAAIAQGSSERSISAVIAETDGPRALAHVHGRCFG 462  Myxococcus xanthus DK 1622

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