Gene: HADHA (HGNC), UniProt P40939, "Trifunctional enzyme subunit alpha, mitochondrial"
(ECHA_HUMAN). Synonym HADH; AltName "78 kDa gastrin-binding protein", "TP-alpha".
HADHA is the alpha subunit of the mitochondrial trifunctional protein (MTP/TFP), an
alpha2-beta2 heterotetramer with HADHB. The alpha subunit carries TWO of the three
catalytic activities of long-chain fatty acid beta-oxidation:
- Long-chain enoyl-CoA hydratase (LCEH), EC 4.2.1.17 (step 2 of each cycle)
- Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD), EC 1.1.1.211 (step 3)
The beta subunit (HADHB) carries the 3-ketoacyl-CoA thiolase (step 4).
[UniProt P40939 DE: "Includes: RecName: Full=Long-chain enoyl-CoA hydratase; Short=LCEH;
EC=4.2.1.17" and "RecName: Full=Long chain 3-hydroxyacyl-CoA dehydrogenase; Short=LCHAD;
EC=1.1.1.211"]
[UniProt FUNCTION: "the trifunctional enzyme subunit alpha/HADHA described here carries the
2,3-enoyl-CoA hydratase and the 3-hydroxyacyl-CoA dehydrogenase activities while the
trifunctional enzyme subunit beta/HADHB bears the 3-ketoacyl-CoA thiolase activity"]
Subunit-specific activity assignment — the definitive paper:
[PMID:8135828 "Expression of this cDNA in mammalian cells yielded a polypeptide with the
long-chain enoyl-CoA hydratase and long-chain 3-hydroxyacyl-CoA dehydrogenase activities."
(alpha-subunit); and beta-subunit cDNA "yielded a polypeptide with the long-chain
3-ketoacyl-CoA thiolase activity."] This is the basis for assigning hydratase+dehydrogenase
to HADHA and thiolase to HADHB.
Original multifunctional-enzyme characterization (whole complex, did not separate subunit
activities; full_text_unavailable):
PMID:1550553 Also: "gives maximum activity with 3-ketoacyl-CoA substrates of C10 to
C16 acyl-chain length" — long-chain specificity.
Catalytic heterogeneity in patient enzymes (full_text_unavailable):
PMID:8163672
Cryo-EM (full_text_unavailable):
[PMID:29915090 "The mitochondrial trifunctional protein (TFP) catalyzes three reactions in
the fatty acid beta-oxidation process." / "Here we report a 4.2-Å cryo-electron microscopy
α2β2 tetrameric structure of the human TFP." / "A concave surface of the TFP tetramer
interacts with the detergent molecules in the structure, suggesting that this region is
involved in associating with the membrane."]
Crystal structure / metabolon, places active sites (full_text_unavailable):
[PMID:30850536 "Membrane-bound mitochondrial trifunctional protein (TFP) catalyzes
β-oxidation of long chain fatty acyl-CoAs, employing 2-enoyl-CoA hydratase (ECH),
3-hydroxyl-CoA dehydrogenase (HAD), and 3-ketothiolase (KT) activities consecutively." /
"The biological unit of the protein is α2β2" / "two α-subunits are bound to each side of the
β2 dimer, creating an arc, which binds on its concave side to the mitochondrial
innermembrane." / "The catalytic residues in all three active sites are arranged similarly to
those of the corresponding, soluble monofunctional enzymes."] ECH and HAD active sites are in
the alpha subunit; KT in beta.
These two structural papers and ComplexPortal support: located_in mitochondrial inner
membrane (GO:0005743) and part_of mitochondrial fatty acid beta-oxidation multienzyme complex
(GO:0016507).
[PMID:23152787 "We previously identified a human monolysocardiolipin acyltransferase activity
which remodels CL via acylation of monolysocardiolipin (MLCL) to CL and was identical to the
alpha subunit of trifunctional protein (αTFP) lacking the first 227 amino acids." / "Purified
human recombinant αTFP exhibited acyl-CoA acyltransferase activity in the acylation of MLCL to
CL with linoleoyl-CoA, oleoyl-CoA and palmitoyl-CoA as substrates." / "we provide a link
between mitochondrial β-oxidation and CL remodeling."] Supports GO:0035965 cardiolipin
acyl-chain remodeling (IDA). UniProt assigns EC=2.3.1.- (MLCL acyltransferase) on ECO:0000305.
iPSC cardiomyocyte model confirms requirement for both BOTH beta-oxidation and CL remodeling:
PMID:31604922 Supports
GO:0006635 (IMP) and GO:0035965 (IMP).
GO:0052816 "long-chain fatty acyl-CoA hydrolase activity" IDA / PMID:22586271. The cited
paper (full_text_available: true) is about the Hotdog-fold thioesterase Them5/Acot15 and
makes NO mention of HADHA/TFP/P40939 anywhere in the abstract or full text. This is a
wrong-paper attribution; HADHA is not a thioesterase. -> REMOVE; reference flagged
WRONG_IDENTIFIER/MISCITED for this claim.
[PMID:22586271 abstract is entirely about: "a new mammalian mitochondrial thioesterase,
Them5"; "Them5 shows strong thioesterase activity with long-chain acyl-CoAs."]
GO:0003985 "acetyl-CoA C-acetyltransferase activity" TAS / PMID:8135828. This is the
THIOLASE activity, which PMID:8135828 explicitly localizes to the BETA subunit (HADHB),
NOT the alpha subunit (HADHA). An old PINC annotation that incorrectly attributes a beta
activity to alpha. -> REMOVE (contradicted by the very paper cited and by structure).
GO:0003857 "(3S)-3-hydroxyacyl-CoA dehydrogenase (NAD+) activity" — this is correct for
HADHA (the dehydrogenase). But the more specific GO:0016509 "long-chain (3S)-3-hydroxyacyl-
CoA dehydrogenase (NAD+) activity" is preferred because HADHA is long-chain specific.
GO:0018812 "3-hydroxyacyl-CoA dehydratase activity" (EXP, PMID:1550553/8135828; and IEA
RHEA). NOTE: this term is the trans-2-enoyl-CoA hydratase reaction (RHEA:16105) which is
the SAME reaction as enoyl-CoA hydratase (GO:0004300). The "dehydratase" framing is the
reverse direction. This is the alpha hydratase activity; correct in essence but
GO:0004300 (enoyl-CoA hydratase activity) is the conventional MF term. Treat the
GO:0018812 entries as MODIFY -> GO:0004300, or KEEP_AS_NON_CORE since it captures the same
reaction. I will MODIFY to enoyl-CoA hydratase.
GO:0042645 "mitochondrial nucleoid" IDA / PMID:18063578. The paper found metabolic
proteins in native nucleoid preps but they did NOT cross-link to mtDNA (peripheral
association). Keep as non-core. PMID:18063578
protein binding (GO:0005515) x7 IPI — generic; KEEP_AS_NON_CORE per curation guidelines
(avoid endorsing bare protein binding as core). Partners include P55084 (HADHB, the
obligate complex partner; PMID:28514442, 29915090, 30850536, 33961781, 40205054) and
autophagy/interactome partners (PMID:20562859, 32814053).
HADHA deficiency causes isolated LCHAD deficiency and generalized MTP deficiency:
hypoketotic hypoglycemia, cardiomyopathy, peripheral neuropathy, pigmentary retinopathy;
maternal HELLP/AFLP (acute fatty liver of pregnancy) when carrying an affected fetus. The
common mutation is E510Q (Glu510Gln) [UniProt VARIANT LCHAD DEFICIENCY GLN-510; PMID:7811722,
PMID:7846063]. Disease relationships are background, not GO MF/BP/CC annotations.
Two MF core functions for HADHA:
- GO:0004300 enoyl-CoA hydratase activity (LCEH, EC 4.2.1.17)
- GO:0016509 long-chain (3S)-3-hydroxyacyl-CoA dehydrogenase (NAD+) activity (LCHAD, EC 1.1.1.211)
Both: directly_involved_in GO:0006635 fatty acid beta-oxidation; locations GO:0005743
mitochondrial inner membrane; in_complex GO:0016507.
A third, independent (subunit-beta-independent) activity: monolysocardiolipin acyltransferase
in cardiolipin remodeling (GO:0035965), arguably a secondary/non-core but well-supported
moonlighting function.