L-isoleucine catabolism in Rhodospirillum rubrum ATCC 11170

GapMind for catabolism of small carbon sources

L-isoleucine catabolism in Rhodospirillum rubrum ATCC 11170

Best path

livF, livG, livJ, livH, livM, ofo, acdH, ech, ivdG, fadA, prpC, prpD, acn, prpB

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 (38 with candidates)

Or see definitions of steps

Step	Description	Best candidate	2nd candidate
livF	L-isoleucine ABC transporter, ATPase component 1 (LivF/BraG)	Rru_A1748	Rru_A3725
livG	L-isoleucine ABC transporter, ATPase component 2 (LivG/BraF)	Rru_A1749	Rru_A3724
livJ	L-isoleucine ABC transporter, substrate-binding component (LivJ/LivK/BraC/BraC3)	Rru_A2171	Rru_A1746
livH	L-isoleucine ABC transporter, permease component 1 (LivH/BraD)	Rru_A1751	Rru_A3726
livM	L-isoleucine ABC transporter, permease component 2 (LivM/BraE)	Rru_A1750	Rru_A3727
ofo	branched-chain alpha-ketoacid:ferredoxin oxidoreductase, fused	Rru_A2185
acdH	(2S)-2-methylbutanoyl-CoA dehydrogenase	Rru_A1835	Rru_A1948
ech	2-methyl-3-hydroxybutyryl-CoA hydro-lyase	Rru_A3801	Rru_A1309
ivdG	3-hydroxy-2-methylbutyryl-CoA dehydrogenase	Rru_A1507	Rru_A0273
fadA	2-methylacetoacetyl-CoA thiolase	Rru_A1380	Rru_A0274
prpC	2-methylcitrate synthase	Rru_A2319	Rru_A1600
prpD	2-methylcitrate dehydratase	Rru_A2318
acn	(2R,3S)-2-methylcitrate dehydratase	Rru_A3511
prpB	2-methylisocitrate lyase	Rru_A2320
Alternative steps:
acnD	2-methylcitrate dehydratase (2-methyl-trans-aconitate forming)	Rru_A3511
Bap2	L-isoleucine permease Bap2
bcaP	L-isoleucine uptake transporter BcaP/CitA
bkdA	branched-chain alpha-ketoacid dehydrogenase, E1 component alpha subunit	Rru_A1881
bkdB	branched-chain alpha-ketoacid dehydrogenase, E1 component beta subunit	Rru_A1880
bkdC	branched-chain alpha-ketoacid dehydrogenase, E2 component	Rru_A1214	Rru_A1879
brnQ	L-isoleucine:cation symporter BrnQ/BraZ/BraB
dddA	3-hydroxypropionate dehydrogenase
epi	methylmalonyl-CoA epimerase	Rru_A1572
hpcD	3-hydroxypropionyl-CoA dehydratase	Rru_A3801	Rru_A2506
iolA	malonate semialdehyde dehydrogenase (CoA-acylating)	Rru_A2071	Rru_A1542
lpd	branched-chain alpha-ketoacid dehydrogenase, E3 component	Rru_A1878	Rru_A1215
mcm-large	methylmalonyl-CoA mutase, large (catalytic) subunit	Rru_A2479	Rru_A3062
mcm-small	methylmalonyl-CoA mutase, small (adenosylcobamide-binding) subunit	Rru_A3062	Rru_A2479
mcmA	methylmalonyl-CoA mutase, fused catalytic and adenosylcobamide-binding components	Rru_A2479	Rru_A2480
natA	L-isoleucine ABC transporter, ATPase component 1 (NatA)	Rru_A3414	Rru_A3724
natB	L-isoleucine ABC transporter, substrate-binding component NatB	Rru_A1746
natC	L-isoleucine ABC transporter, permease component 1 (NatC)	Rru_A3415
natD	L-isoleucine ABC transporter, permease component 2 (NatD)	Rru_A3416	Rru_A3306
natE	L-isoleucine ABC transporter, ATPase component 2 (NatE)	Rru_A3413	Rru_A1748
ofoA	branched-chain alpha-ketoacid:ferredoxin oxidoreductase, alpha subunit OfoA	Rru_A2721
ofoB	branched-chain alpha-ketoacid:ferredoxin oxidoreductase, beta subunit OfoB	Rru_A2722
pccA	propionyl-CoA carboxylase, alpha subunit	Rru_A0052	Rru_A1941
pccA1	propionyl-CoA carboxylase, biotin carboxyl carrier subunit	Rru_A0052	Rru_A2435
pccA2	propionyl-CoA carboxylase, biotin carboxylase subunit	Rru_A1941
pccB	propionyl-CoA carboxylase, beta subunit	Rru_A0053	Rru_A1943
pco	propanyl-CoA oxidase	Rru_A2005
prpF	methylaconitate isomerase
vorA	branched-chain alpha-ketoacid:ferredoxin oxidoreductase, alpha subunit VorA
vorB	branched-chain alpha-ketoacid:ferredoxin oxidoreductase, beta subunit VorB	Rru_A2721
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