lactose catabolism in Escherichia coli BW25113

GapMind for catabolism of small carbon sources

lactose catabolism in Escherichia coli BW25113

Best path

lacY, lacZ, galK, galT, galE, pgmA, glk

Also see fitness data for the top candidates

Rules

Overview: Lactose utilization in GapMind is based on MetaCyc pathway lactose degradation II via 3'-ketolactose (link), pathway III via beta-galactosidase (link), or uptake by a PTS system followed by hydrolysis of lactose 6'-phosphate. (There is no pathway I.)

all:

lactose-transport, beta-galactosidase, galactose-degradation and glk
or lactose-PTS, pbgal, galactose-6-phosphate-degradation and glk
or lacA', lacC', lacB', klh and glucose-utilization
Comment: In pathway III, lactose is taken up and cleaved to galactose and glucose by beta-galactosidase; the glucose is consumed by kinase glk. (The galactose 1-epimerase galM, EC 5.1.3.3, is not included in galactose degradation; it is important for lactose utilization in E. coli (PMID:7966338), but not in Sinorhizobium meliloti or in Bacteroides thetaiotaomicron, which also use this pathway.) Or, a PTS forms lactose 6'-phosphate and phosphogalactosidase (pbgal) forms galactose 6-phosphate and glucose. Or, lactose is oxidized to 3'-ketolactose by a periplasmic 3-component dehydrogenase (lacACB'), and then hydrolyzed by a periplasmic enzyme (klh) to 3-keto-beta-D-galactose and D-glucopyranose, and hypothetical reduction of the 3-ketogalactose. Liberation of glucose is probably sufficient for growth.

beta-galactosidase:

lacZ
or lacL and lacM
Comment: Most lactases are homomeric, but Lactobacillus have a heteromeric enzyme LacLM. (There is also a heteromeric beta-galactosidase in barley, see BGAL_HORVU, but it is not included. Also, "evolved beta-galactosidase" ebgA from E. coli is more active with its partner ebgC, but it retains activity on its own, so it is included in step lacZ instead.)

glucose-utilization:

glucose-transport and glk
or glucose-PTS
or gdh, gnl, gadh1, gadh2, gadh3, kguT, kguK, kguD, edd and eda
Comment: Glucose can be taken up and then phosphorylated to glucose 6-phosphate by the kinase glk. Or, both uptake and phosphorylation are catalyzed by a PTS system. Or, glucose is oxidized to glucono-1,5-lactone in the periplasm (by gdh), hydrolyzed to gluconate (by gnl), oxidized to 2-ketogluconate (by gadh123), taken up by kguT, phosphorylated to 2-dehydro-6-phosphogluconate (by kguK), reduced to gluconate 6-phosphate (by kguD), dehydrated by edd to 2-dehydro-3-deoxy-gluconate 6-phosphate, and cleaved by aldolase eda to pyruvate and D-glyceraldehyde 3-phosphate.

glucose-PTS:

ptsG-crr
or bglF
or ptsG and crr
or manX, manY and manZ

glucose-transport:

MFS-glucose
or SSS-glucose
or glcU'
or PAST-A
or SemiSWEET
or SWEET1
or mglA, mglB and mglC
or gtsA, gtsB, gtsC and gtsD
or glcS, glcT, glcU and glcV
or aglE', aglF', aglG' and aglK'
Comment: Transporters and PTS systems were analyzed uzing query: transporter:glucose:D-glucose:D-glucopyranose:ALPHA-GLUCOSE:GLC:CPD-15374

galactose-degradation:

galK, galT, galE and pgmA
or galdh, galactonolactonase, dgoD, dgoK and dgoA
Comment: In the Leloir pathway, galactokinase (galK) forms galactose 1-phosphate, a uridyltransferase (galT) uses glucose 1-phosphate to form UDP-galactose, an epimerase (galE) forms UDP-glucose, and this is converted to glucose 1-phosphate by the same uridyltransferase. (We initially included the 1-epimerase galM, EC 5.1.3.3, in our model of the Leloir pathway, but found that in most bacteria, galM proteins were not important for fitness during growth on galactose; the only exception was Echvi_0697.) The oxidative pathway begins with oxidation to a lactone (by galdh) and hydrolysis to galactonate; galactonate is then dehydrated, phosphorylated, and cleaved by an aldolase.

galactose-6-phosphate-degradation: lacA, lacB, lacC, tag16P-aldolase and tpi

Comment: The tagatose 6-phosphate pathway involves the isomerization of galactose 6-phosphate to tagatose-6-phosphate (by lacAB), phosphorylation to tagatose 1,6-bisphosphate (by lacC), and an aldolase.

tag16P-aldolase:

lacD
or gatY and gatZ
Comment: Two forms of D-tagatose-1,6-phosphate aldolase are known, homomeric (lacD) or heteromeric (gatYZ or kbaYZ)

lactose-PTS:

lacIIA, lacIIB and lacIIC
or lacIIA and lacIICB
Comment: PTS systems forming lactose 6'-phosphate. Klebsiella pneumoniae has a EIIA,B,C in three separate proteins. The other characterized PTS systems have EIIA and EIICB

lactose-transport:

lacE, lacF, lacG and lacK
or lacP
or lacS
or lacY
Comment: Transporters and PTS systems were identified using query: transporter:lactose:alpha-lactose:CPD-15971

74 steps (46 with candidates)

Or see definitions of steps

Step	Description	Best candidate	2nd candidate
lacY	lactose:proton symporter LacY	b0343
lacZ	lactase (homomeric)	b3076	b0344
galK	galactokinase (-1-phosphate forming)	b0757
galT	UDP-glucose:alpha-D-galactose-1-phosphate uridylyltransferase	b0758
galE	UDP-glucose 4-epimerase	b0759	b2041
pgmA	alpha-phosphoglucomutase	b0688	b2048
glk	glucokinase	b2388	b0394
Alternative steps:
aglE'	glucose ABC transporter, substrate-binding component (AglE)
aglF'	glucose ABC transporter, permease component 1 (AglF)
aglG'	glucose ABC transporter, permease component 2 (AglG)	b4032
aglK'	glucose ABC transporter, ATPase component (AglK)	b4035	b3450
bglF	glucose PTS, enzyme II (BCA components, BglF)	b3722	b2715
crr	glucose PTS, enzyme IIA	b2417	b0679
dgoA	2-dehydro-3-deoxy-6-phosphogalactonate aldolase	b1850	b4477
dgoD	D-galactonate dehydratase	b4478	b4297
dgoK	2-dehydro-3-deoxygalactonokinase	b3693	b3526
eda	2-keto-3-deoxygluconate 6-phosphate aldolase	b1850	b4477
edd	phosphogluconate dehydratase	b1851	b3771
gadh1	gluconate 2-dehydrogenase flavoprotein subunit
gadh2	gluconate 2-dehydrogenase cytochrome c subunit
gadh3	gluconate 2-dehydrogenase subunit 3
galactonolactonase	galactonolactonase (either 1,4- or 1,5-lactone)	b3379
galdh	D-galactose 1-dehydrogenase (forming 1,4- or 1,5-lactones)	b2426	b2842
gatY	D-tagatose-1,6-bisphosphate aldolase, catalytic subunit (GatY/KbaY)	b3137	b2096
gatZ	D-tagatose-1,6-bisphosphate aldolase, chaperone subunit (GatZ/KbaZ)	b3132	b2095
gdh	quinoprotein glucose dehydrogenase	b0124	b0837
glcS	glucose ABC transporter, substrate-binding component (GlcS)
glcT	glucose ABC transporter, permease component 1 (GlcT)
glcU	glucose ABC transporter, permease component 2 (GlcU)
glcU'	Glucose uptake protein GlcU
glcV	glucose ABC transporter, ATPase component (GclV)	b0262	b4035
gnl	gluconolactonase
gtsA	glucose ABC transporter, substrate-binding component (GtsA)
gtsB	glucose ABC transporter, permease component 1 (GtsB)
gtsC	glucose ABC transporter, permease component 2 (GtsC)	b1312	b4032
gtsD	glucose ABC transporter, ATPase component (GtsD)	b4035	b3450
kguD	2-keto-6-phosphogluconate reductase	b3553	b2913
kguK	2-ketogluconokinase
kguT	2-ketogluconate transporter
klh	periplasmic 3'-ketolactose hydrolase
lacA	galactose-6-phosphate isomerase, lacA subunit	b4090
lacA'	periplasmic lactose 3-dehydrogenase, LacA subunit
lacB	galactose-6-phosphate isomerase, lacB subunit	b4090
lacB'	periplasmic lactose 3-dehydrogenase, cytochrome c component (LacB)
lacC	D-tagatose-6-phosphate kinase	b3916	b1723
lacC'	periplasmic lactose 3-dehydrogenase, LacC subunit
lacD	D-tagatose-1,6-bisphosphate aldolase (monomeric)
lacE	lactose ABC transporter, substrate-binding component
lacF	lactose ABC transporter, permease component 1	b1311
lacG	lactose ABC transporter, permease component 2
lacIIA	lactose PTS system, EIIA component	b1736
lacIIB	lactose PTS system, EIIB component	b1738
lacIIC	lactose PTS system, EIIC component	b1737
lacIICB	lactose PTS system, fused EIIC and EIIB components
lacK	lactose ABC transporter, ATPase component	b4035	b3450
lacL	heteromeric lactase, large subunit	b0344	b3076
lacM	heteromeric lactase, small subunit
lacP	lactose permease LacP
lacS	lactose permease LacS
manX	glucose PTS, enzyme EIIAB	b1817
manY	glucose PTS, enzyme EIIC	b1818
manZ	glucose PTS, enzyme EIID	b1819	b3140
MFS-glucose	glucose transporter, MFS superfamily	b2943	b2841
mglA	glucose ABC transporter, ATP-binding component (MglA)	b2149	b3567
mglB	glucose ABC transporter, substrate-binding component	b2150	b3566
mglC	glucose ABC transporter, permease component (MglC)	b2148	b3750
PAST-A	proton-associated sugar transporter A
pbgal	phospho-beta-galactosidase	b3721	b2901
ptsG	glucose PTS, enzyme IICB	b1101	b0679
ptsG-crr	glucose PTS, enzyme II (CBA components, PtsG)	b0679	b1101
SemiSWEET	Sugar transporter SemiSWEET
SSS-glucose	Sodium/glucose cotransporter	b3679
SWEET1	bidirectional sugar transporter SWEET1
tpi	triose-phosphate isomerase	b3919	b2926

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 17 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