L-isoleucine catabolism in Methylocapsa acidiphila B2

GapMind for catabolism of small carbon sources

L-isoleucine catabolism in Methylocapsa acidiphila B2

Best path

livF, livG, livJ, livH, livM, ofo, acdH, ech, ivdG, fadA, pccA, pccB, epi, mcm-large, mcm-small

Rules

Overview: Isoleucine degradation in GapMind is based on MetaCyc pathway L-isoleucine degradation I (link). The other pathways are fermentative and do not lead to carbon incorporation (link, link).

all: isoleucine-transport, BKD, acdH, ech, ivdG, fadA and propionyl-CoA-degradation

Comment: A transaminase (which is not represented) converts isoleucine to (3S)-3-methyl-2-oxopentanoate, the decarboxylating dehydrogenase BKD forms (2S)-2-methylbutanoyl-CoA, dehydrogenase acdH forms (E)-2-methylcrotonyl-CoA, hydratase ech forms (2S,3S)-3-hydroxy-2-methylbutanoyl-CoA, dehydrogenase ivdG forms 2-methylacetoacetyl-CoA, and a thiolase forms propanioyl-CoA and acetyl-CoA. (The initial transaminase is not represented because amino-acid aminotransferases are often non-specific.)

BKD:

bkdA, bkdB, bkdC and lpd
or vorA, vorB and vorC
or ofoA and ofoB
or ofo
Comment: These decarboxylating dehydrogenases act on 4-methyl-2-oxopentanoate, 3-methyl-2-oxobutanoate (2-oxoisovalerate) and (S)-3-methyl-2-oxopentanoate and are known as the branched-chain alpha-ketoacid dehydrogenases. They can pass electrons to NAD (EC 1.2.1.25) or to ferredoxin (EC 1.2.7.7). The NAD-dependent enzyme is the sum of three activities: EC 1.2.4.4 (the 4-methyl-2-oxopentanoate dehydrogenase, with transfer to the lipopoyllysine residue of 2.3.1.168) which is itself heteromeric, with alpha and beta subunits; EC 2.3.1.168 (dihydrolipoyllysine-residue (3-methylbutanoyl)transferase); and EC 1.8.1.4 (dihydrolipoyl dehydrogenase, transferring electrons to NAD). The well-characterized ferredoxin-dependent enzymes have 3 subunits (vorABC) or 2 subunits (ofoAB). Genetic data identified a fused ferredoxin-dependent enzyme with just 1 subunit (ofo).

propionyl-CoA-degradation:

prpC, prpD, acn and prpB
or prpC, acnD, prpF, acn and prpB
or propionyl-CoA-carboxylase, epi and methylmalonyl-CoA-mutase
or pco, hpcD, dddA and iolA
Comment: In 2-methylcitrate cycle I, propionyl-CoA is combined with oxalacetate (by prpC) to give methylcitrate, dehydrated to cis-2-methylaconitate by prpD, hydrated to (2R,3S)-2-methylisocitrate, and a lyase produces pyruvate and succinate. (We consider succinate as a central intermediate, as most organisms can activate it to succinyl-CoA or can oxidize it to fumarate and convert that to oxaloacetate.) In 2-methylcitrate cycle II, a different dehydratase (acnD) and an isomerase (prpF) replace the dehydratase prpD; acnD dehydrates (2S,3S)-2-methylcitrate to 2-methyl-trans-aconitate, and prpF isomerizes it to cis-2-methylaconitate. In propanoyl CoA degradation I, propionyl-CoA carboxylase forms (S)-methylmalonyl-CoA, methylmalonyl-CoA epimerase forms (R)-methylmalonyl-CoA, and methylmalonyl-CoA mutase forms succinyl-CoA, which is a central metabolite. (Note that methylmalonyl-CoA mutase requires adenosylcobamide, a form of vitamin B12, for activity.) In propanoyl-CoA degradation II: propionyl-CoA is oxidized to acrylyl-CoA by pco, hydrated to 3-hydroxypropionyl-CoA, hydrolzed to 3-hydroxypropionate, oxidized to 3-oxopropionate (malonate semialdehyde), and oxidized to acetyl-CoA and CO2.

methylmalonyl-CoA-mutase:

mcmA
or mcm-large and mcm-small
Comment: methylmalonyl-CoA mutase has a catalytic domain and a B12-binding domain. These are usually found in the same protein, which we call mcmA. In Metallosphaera and Pyrococcus, the B12-binding domain is a separate subunit. In Propionibacterium and Methylorubrum, there is an additional subunit with a catalytic domain only; this may have a protective role (PMID:14734568) and is not described here. There's also a mcm-interacting GTPase (known as MeaB or YgfD) that loads B12 onto mcm and protects it from inactivation (see PMC4631608); this is not described here. Some fused mcm proteins include a MeaB domain as well (i.e., Q8F222, Q8Y2U5).

propionyl-CoA-carboxylase:

pccA and pccB
or pccA1, pccA2 and pccB
Comment: propionyl-CoA carboxylase is a heteromer, usually with alpha and beta subunits pccAB. Haloferax mediterranei has a third subunit as well (pccX), which is not described here. Acidianus brierleyi has a diverged pccA split into two pieces.

isoleucine-transport:

livF, livG, livJ, livH and livM
or natA, natB, natC, natD and natE
or Bap2
or brnQ
or bcaP
Comment: Transporters were identified using query: transporter:isoleucine:L-isoleucine:ile and non-specific large neutral amino acid tranpsorters from mammals were ignored.

45 steps (33 with candidates)

Or see definitions of steps

Step	Description	Best candidate	2nd candidate
livF	L-isoleucine ABC transporter, ATPase component 1 (LivF/BraG)	METAC_RS0107800	METAC_RS0120245
livG	L-isoleucine ABC transporter, ATPase component 2 (LivG/BraF)	METAC_RS0107795	METAC_RS0120250
livJ	L-isoleucine ABC transporter, substrate-binding component (LivJ/LivK/BraC/BraC3)	METAC_RS0107810	METAC_RS24715
livH	L-isoleucine ABC transporter, permease component 1 (LivH/BraD)	METAC_RS0107785	METAC_RS0120260
livM	L-isoleucine ABC transporter, permease component 2 (LivM/BraE)	METAC_RS0107790	METAC_RS0120255
ofo	branched-chain alpha-ketoacid:ferredoxin oxidoreductase, fused	METAC_RS0120625
acdH	(2S)-2-methylbutanoyl-CoA dehydrogenase	METAC_RS0105115	METAC_RS0108105
ech	2-methyl-3-hydroxybutyryl-CoA hydro-lyase	METAC_RS0108535	METAC_RS0106925
ivdG	3-hydroxy-2-methylbutyryl-CoA dehydrogenase	METAC_RS0103870	METAC_RS0107660
fadA	2-methylacetoacetyl-CoA thiolase	METAC_RS0107670	METAC_RS0102805
pccA	propionyl-CoA carboxylase, alpha subunit	METAC_RS0107890	METAC_RS0105105
pccB	propionyl-CoA carboxylase, beta subunit	METAC_RS0107875	METAC_RS0105110
epi	methylmalonyl-CoA epimerase	METAC_RS0108340
mcm-large	methylmalonyl-CoA mutase, large (catalytic) subunit	METAC_RS0104845
mcm-small	methylmalonyl-CoA mutase, small (adenosylcobamide-binding) subunit	METAC_RS0104845
Alternative steps:
acn	(2R,3S)-2-methylcitrate dehydratase	METAC_RS0113690
acnD	2-methylcitrate dehydratase (2-methyl-trans-aconitate forming)	METAC_RS0113690
Bap2	L-isoleucine permease Bap2
bcaP	L-isoleucine uptake transporter BcaP/CitA	METAC_RS22315
bkdA	branched-chain alpha-ketoacid dehydrogenase, E1 component alpha subunit	METAC_RS0116100	METAC_RS0105865
bkdB	branched-chain alpha-ketoacid dehydrogenase, E1 component beta subunit	METAC_RS0116105	METAC_RS0105870
bkdC	branched-chain alpha-ketoacid dehydrogenase, E2 component	METAC_RS0116110	METAC_RS0118195
brnQ	L-isoleucine:cation symporter BrnQ/BraZ/BraB
dddA	3-hydroxypropionate dehydrogenase
hpcD	3-hydroxypropionyl-CoA dehydratase	METAC_RS0108535	METAC_RS0106925
iolA	malonate semialdehyde dehydrogenase (CoA-acylating)	METAC_RS0111815	METAC_RS0109380
lpd	branched-chain alpha-ketoacid dehydrogenase, E3 component	METAC_RS0105880	METAC_RS0118190
mcmA	methylmalonyl-CoA mutase, fused catalytic and adenosylcobamide-binding components	METAC_RS0104845
natA	L-isoleucine ABC transporter, ATPase component 1 (NatA)	METAC_RS0120250	METAC_RS0107795
natB	L-isoleucine ABC transporter, substrate-binding component NatB
natC	L-isoleucine ABC transporter, permease component 1 (NatC)
natD	L-isoleucine ABC transporter, permease component 2 (NatD)	METAC_RS0120260
natE	L-isoleucine ABC transporter, ATPase component 2 (NatE)	METAC_RS0120245	METAC_RS0107800
ofoA	branched-chain alpha-ketoacid:ferredoxin oxidoreductase, alpha subunit OfoA
ofoB	branched-chain alpha-ketoacid:ferredoxin oxidoreductase, beta subunit OfoB
pccA1	propionyl-CoA carboxylase, biotin carboxyl carrier subunit	METAC_RS0107890	METAC_RS0119920
pccA2	propionyl-CoA carboxylase, biotin carboxylase subunit	METAC_RS0105105
pco	propanyl-CoA oxidase	METAC_RS0108105
prpB	2-methylisocitrate lyase
prpC	2-methylcitrate synthase	METAC_RS0114560
prpD	2-methylcitrate dehydratase
prpF	methylaconitate isomerase	METAC_RS22635
vorA	branched-chain alpha-ketoacid:ferredoxin oxidoreductase, alpha subunit VorA
vorB	branched-chain alpha-ketoacid:ferredoxin oxidoreductase, beta subunit VorB
vorC	branched-chain alpha-ketoacid:ferredoxin oxidoreductase, gamma subunit VorC

Confidence: high confidence medium confidence low confidence
transporter – transporters and PTS systems are shaded because predicting their specificity is particularly challenging.

This GapMind analysis is from Sep 24 2021. The underlying query database was built on Sep 17 2021.

Downloads

Candidates (tab-delimited)
Steps (tab-delimited)
Rules (tab-delimited)
Protein sequences (fasta format)
Organisms (tab-delimited)
SQLite3 databases

Related tools

About GapMind

Each pathway is defined by a set of rules based on individual steps or genes. Candidates for each step are identified by using ublast (a fast alternative to protein BLAST) against a database of manually-curated proteins (most of which are experimentally characterized) or by using HMMer with enzyme models (usually from TIGRFam). Ublast hits may be split across two different proteins.

A candidate for a step is "high confidence" if either:

ublast finds a hit to a characterized protein at above 40% identity and 80% coverage, and bits >= other bits+10.
- (Hits to curated proteins without experimental data as to their function are never considered high confidence.)
HMMer finds a hit with 80% coverage of the model, and either other identity < 40 or other coverage < 0.75.

where "other" refers to the best ublast hit to a sequence that is not annotated as performing this step (and is not "ignored").

Otherwise, a candidate is "medium confidence" if either:

ublast finds a hit at above 40% identity and 70% coverage (ignoring otherBits).
ublast finds a hit at above 30% identity and 80% coverage, and bits >= other bits.
HMMer finds a hit (regardless of coverage or other bits).

Other blast hits with at least 50% coverage are "low confidence."

Steps with no high- or medium-confidence candidates may be considered "gaps." For the typical bacterium that can make all 20 amino acids, there are 1-2 gaps in amino acid biosynthesis pathways. For diverse bacteria and archaea that can utilize a carbon source, there is a complete high-confidence catabolic pathway (including a transporter) just 38% of the time, and there is a complete medium-confidence pathway 63% of the time. Gaps may be due to:

our ignorance of proteins' functions,
omissions in the gene models,
frame-shift errors in the genome sequence, or
the organism lacks the pathway.

GapMind relies on the predicted proteins in the genome and does not search the six-frame translation. In most cases, you can search the six-frame translation by clicking on links to Curated BLAST for each step definition (in the per-step page).

For more information, see:

the paper from 2019 on GapMind for amino acid biosynthesis
the paper from 2022 on GapMind for carbon sources
the source code
instructions for running GapMind on your computer

If you notice any errors or omissions in the step descriptions, or any questionable results, please let us know

by Morgan Price, Arkin group, Lawrence Berkeley National Laboratory

GapMind for catabolism of small carbon sources