The C4-dicarboxylate uptake family or Dcu family
TC# 2.A.13
is a

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

of transmembrane

ion transporter In biology, a transporter is a transmembrane protein that moves ions (or other small molecules) across a biological membrane to accomplish many different biological functions including, cellular communication, maintaining homeostasis, energy produc ...

s found in bacteria. Their function is to exchange

dicarboxylate In organic chemistry, a carboxylate is the conjugate base of a carboxylic acid, (or ). It is an ion with negative charge. Carboxylate salts are salts that have the general formula , where M is a metal and ''n'' is 1, 2,...; ''carboxylat ...

s such as

aspartate Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins. Like all other amino acids, it contains an amino group and a carboxylic acid. Its α-amino group is in the pro ...

malate Malic acid is an organic compound with the molecular formula . It is a dicarboxylic acid that is made by all living organisms, contributes to the sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms (L ...

fumarate Fumaric acid is an organic compound with the formula HO2CCH=CHCO2H. A white solid, fumaric acid occurs widely in nature. It has a fruit-like taste and has been used as a food additive. Its E number is E297. The salts and esters are known as f ...

and

succinate Succinic acid () is a dicarboxylic acid with the chemical formula (CH2)2(CO2H)2. The name derives from Latin ''succinum'', meaning amber. In living organisms, succinic acid takes the form of an anion, succinate, which has multiple biological ro ...

Structure

Many members of this family are predicted to have 11 or 12

transmembrane A transmembrane protein (TP) is a type of integral membrane protein that spans the entirety of the cell membrane. Many transmembrane proteins function as gateways to permit the transport of specific substances across the membrane. They frequentl ...

regions (TMSs); however, one member of this family (Uncharacterized protein of ''Encarsia pergandiella'' symbiont, ''Cardinium hertigii'', strain ''c''Eper1
TC# 2.A.13.2.1
is reported to have 10 transmembrane regions, with both the N- and C-termini localized to the

periplasm The periplasm is a concentrated gel-like matrix in the space between the inner cytoplasmic membrane and the bacterial outer membrane called the ''periplasmic space'' in gram-negative bacteria. Using cryo-electron microscopy it has been found that ...

. For DcuA, the 'positive inside' rule is obeyed, and two putative TMSs are localized to a cytoplasmic loop between TMSs 5 and 6 and in the C-terminal periplasmic region. The fully sequenced proteins are of fairly uniform size, from 434-446 amino acyl residues in length. There are no crystal structures available for members of the Dcu family.

Function

The two ''E. coli'' proteins, DcuA
TC# 2.A.13.1.1
and DcuB
TC# 2.A.13.1.2
, of the Dcu family are involved in the

transport Transport (in British English), or transportation (in American English), is the intentional movement of humans, animals, and goods from one location to another. Modes of transport include air, land (rail and road), water, cable, pipeline, an ...

and

, functioning as

antiporter An antiporter (also called exchanger or counter-transporter) is a cotransporter and integral membrane protein involved in secondary active transport of two or more different molecules or ions across a phospholipid membrane such as the plasma memb ...

s with any two of these substrates. They exhibit 36% identity with 63% similarity, and both transport fumarate in exchange for succinate with the same affinity (30 μM). Since DcuA is encoded in an

operon In genetics, an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo splic ...

with the

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

for aspartase, and DcuB is encoded in an operon with the gene for

fumarase Fumarase (or fumarate hydratase) is an enzyme () that catalyzes the reversible hydration/dehydration of fumarate to malate. Fumarase comes in two forms: mitochondrial and cytosolic. The mitochondrial isoenzyme is involved in the Krebs cycle and ...

, their physiological functions may be to

catalyse Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

aspartate:fumarate and fumarate:malate exchange during the

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...

utilization of

and

, respectively. The two transporters can apparently substitute for each other under certain physiological conditions. The generalized transport reaction catalyzed by the proteins of the Dcu family is:

Dicarboxylate₁ (out) + Dicarboxylate₂ (in) ⇌ Dicarboxylate₁ (in) + Dicarboxylate₂ (out).

Expression

The ''

Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...

'' DcuA and DcuB proteins have very different

expression Expression may refer to: Linguistics * Expression (linguistics), a word, phrase, or sentence * Fixed expression, a form of words with a specific meaning * Idiom, a type of fixed expression * Metaphorical expression, a particular word, phrase, o ...

patterns. DcuA is constitutively expressed; DcuB is strongly induced anaerobically by FNR and C4-dicarboxylates, while it is repressed by nitrate and subject to CRP-mediated catabolite repression.

References

{{Portal bar, Biology, border=no Protein families Transmembrane transporters

Structure

Function

Expression

See also

References