Branched-chain amino acid metabolon: interaction of glutamate dehydrogenase with the mitochondrial branched-chain aminotransferase (BCATm).
The catabolic pathway for branched-chain amino acids includes deamination followed by oxidative decarboxylation of the deaminated product branched-chain alpha-keto acids, catalyzed by the mitochondrial branched-chain aminotransferase (BCATm) and branched-chain alpha-keto acid dehydrogenase enzyme complex (BCKDC). We found that BCATm binds to the E1 decarboxylase of BCKDC, forming a metabolon that allows channeling of branched-chain alpha-keto acids from BCATm to E1. The protein complex also contains glutamate dehydrogenase (GDH1), 4-nitrophenylphosphatase domain and non-neuronal SNAP25-like protein homolog 1, pyruvate carboxylase, and BCKDC kinase. GDH1 binds to the pyridoxamine 5'-phosphate (PMP) form of BCATm (PMP-BCATm) but not to the pyridoxal 5'-phosphate-BCATm and other metabolon proteins. Leucine activates GDH1, and oxidative deamination of glutamate is increased further by addition of PMP-BCATm. Isoleucine and valine are not allosteric activators of GDH1, but in the presence of 5'-phosphate-BCATm, they convert BCATm to PMP-BCATm, stimulating GDH1 activity. Sensitivity to ADP activation of GDH1 was unaffected by PMP-BCATm; however, addition of a 3 or higher molar ratio of PMP-BCATm to GDH1 protected GDH1 from GTP inhibition by 50%. Kinetic results suggest that GDH1 facilitates regeneration of the form of BCATm that binds to E1 decarboxylase of the BCKDC, promotes metabolon formation, branched-chain amino acid oxidation, and cycling of nitrogen through glutamate.
Islam
Mohammad Mainul
MM
Department of Human Nutrition, Foods and Exercise, Virginia Polytechnic Institute, Blacksburg, Virginia 24061, USA.
Nautiyal
Manisha
M
Wynn
R Max
RM
Mobley
James A
JA
Chuang
David T
DT
Hutson
Susan M
SM
D000494:Allosteric Regulation / Q000187:drug effects; D000597:Amino Acids, Branched-Chain / Q000378:metabolism*; D000818:Animals; D055162:Biocatalysis / Q000187:drug effects; D002846:Chromatography, Affinity; D003432:Cross-Linking Reagents / Q000494:pharmacology; D003641:Deamination / Q000187:drug effects; D003653:Decarboxylation / Q000187:drug effects; D005969:Glutamate Dehydrogenase / Q000378:metabolism*; D008297:Male; D055442:Metabolome / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology*; D010084:Oxidation-Reduction / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D011733:Pyridoxamine / Q000031:analogs & derivatives / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution / Q000187:drug effects; D000637:Transaminases / Q000378:metabolism*
D000597:Amino Acids, Branched-Chain; D003432:Cross-Linking Reagents; C009123:pyridoxamine 5-thiophosphate; D011733:Pyridoxamine; D005969:Glutamate Dehydrogenase; D000637:Transaminases; C019798:branched-chain-amino-acid transaminase