Digoxigenin (DIG) is a
steroid
A steroid is an organic compound with four fused compound, fused rings (designated A, B, C, and D) arranged in a specific molecular configuration.
Steroids have two principal biological functions: as important components of cell membranes t ...
found exclusively in the flowers and leaves of the plants ''
Digitalis purpurea
''Digitalis purpurea'', the foxglove or common foxglove, is a toxic species of flowering plant in the plantain family Plantaginaceae, native to and widespread throughout most of temperate Europe. It has also naturalized in parts of North Ame ...
'', ''
Digitalis orientalis
''Digitalis'' ( or ) is a genus of about 20 species of herbaceous perennial plants, shrubs, and Biennial plant, biennials, commonly called foxgloves.
''Digitalis'' is native to Europe, Western Asia, and northwestern Africa. The flowers are ...
'' and ''
Digitalis lanata
''Digitalis lanata'', vernacularly often called woolly foxglove or Grecian foxglove, is a species of foxglove, a flowering plant in the plantain family Plantaginaceae. It gets its name due to the woolly indumentum of the leaves. ''D. lanata'', li ...
'' (foxgloves), where it is attached to sugars, to form the
glycoside
In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. ...
s (e.g.
digoxin
Digoxin (better known as digitalis), sold under the brand name Lanoxin among others, is a medication used to treat various heart disease, heart conditions. Most frequently it is used for atrial fibrillation, atrial flutter, and heart failure. ...
,
lanatoside C).
Uses in biotechnology
Digoxigenin is a
hapten
Haptens (derived from the Greek ''haptein'', meaning “to fasten”) are small molecules that elicit an immune response only when attached to a large carrier such as a protein; the carrier may be one that also does not elicit an immune response ...
, a small
molecule
A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
with high
antigenicity, that is used in many molecular biology applications similarly to other popular haptens such as
2,4-Dinitrophenol,
biotin
Biotin (also known as vitamin B7 or vitamin H) is one of the B vitamins. It is involved in a wide range of metabolic processes, both in humans and in other organisms, primarily related to the utilization of fats, carbohydrates, and amino acids. ...
, and
fluorescein
Fluorescein is an organic compound and dye based on the xanthene tricyclic structural motif, formally belonging to Triarylmethane dye, triarylmethine dyes family. It is available as a dark orange/red powder slightly soluble in water and alcohol. ...
. Typically, digoxigenin is introduced chemically (
conjugation
Conjugation or conjugate may refer to:
Linguistics
*Grammatical conjugation, the modification of a verb from its basic form
*Emotive conjugation or Russell's conjugation, the use of loaded language
Mathematics
*Complex conjugation, the change o ...
) into biomolecules (proteins, nucleic acids) to be detected in further assays. K
d of the digoxigenin-antibody interaction has been estimated at ~12 nM (compare to K
d~0.1pM for the biotin-streptavidin interaction).
;DIG-binding proteins
Tinberg et al. designed artificial proteins that bind DIG. Their best binder, DIG10.3, was a 141 amino acid protein that bound DIG with a
dissociation constant
In chemistry, biochemistry, and pharmacology, a dissociation constant (''K''D) is a specific type of equilibrium constant that measures the propensity of a larger object to separate (dissociate) reversibly into smaller components, as when a complex ...
(K
d) of 541 (+/- 193) pM.
Anti-digoxigenin
antibodies
An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that caus ...
with high
affinities and specificity are used in a variety of biological immuno-assays (e.g.
ELISA
The enzyme-linked immunosorbent assay (ELISA) (, ) is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971. The assay is a solid-phase type of enzyme immunoassay (EIA) to detect the presence of ...
). The antibodies are labeled with dyes, enzymes or fluorescence, directly or secondarily, for visualization and detection.
Digoxigenin is thus an all-purpose immuno-tag, and in particular a standard
immunohistochemical
Immunohistochemistry is a form of immunostaining. It involves the process of selectively identifying antigens in cells and tissue, by exploiting the principle of antibodies binding specifically to antigens in biological tissues. Albert Hewett ...
marker for
in situ hybridization
''In situ'' hybridization (ISH) is a type of Hybridisation (molecular biology), hybridization that uses a labeled complementary DNA, RNA or modified nucleic acid strand (i.e., a Hybridization probe, probe) to localize a specific DNA or RNA seq ...
. In this case it is conjugated to a single species of RNA
nucleoside
Nucleosides are glycosylamines that can be thought of as nucleotides without a phosphate group. A nucleoside consists simply of a nucleobase (also termed a nitrogenous base) and a five-carbon sugar (ribose or 2'-deoxyribose) whereas a nucleotid ...
triphosphate (typically
uridine
Uridine (symbol U or Urd) is a glycosylated pyrimidine analog containing uracil attached to a ribose ring (or more specifically, a ribofuranose) via a β-N1- glycosidic bond. The analog is one of the five standard nucleosides which make up nuc ...
), which is then incorporated into RNA (a "
riboprobe A Riboprobe, abbreviation of RNA probe, is a segment of labelled RNA that can be used to detect a target mRNA or DNA during in situ hybridization. RNA Hybridization probe, probes can be produced by ''in vitro'' transcription of cloned DNA inserted i ...
") as it is synthesized by the cellular machinery.
It allows to make :
* sensitive non-radioactive in situ hybridization probes to detect nucleic acids in plants, able to detect 1 μg of plasmid DNA.
* peptide-DIG conjugates, i.e. bradykinin assay by very sensitive chemiluminescence immunoassays.
* fluorescent and DIG-labeled tracers for competitive immunoassays, i.e. to
limit detect digoxin, a drug used to cure cardiac arrhythmia, down to 0.2 ng mL
−1.
* Digoxigenin may be conjugated to
sugars
Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides ...
to study
glycosylation
Glycosylation is the reaction in which a carbohydrate (or ' glycan'), i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor) in order to form a glycoconjugate. In biology (but not ...
events,
even in biological systems.
See also
*
Immunostaining
In biochemistry, immunostaining is any use of an antibody-based method to detect a specific protein in a sample. The term "immunostaining" was originally used to refer to the immunohistochemical staining of tissue sections, as first described by ...
References
{{Reflist
Cardenolides
Triols