Brefeldin A is a
lactone
Lactones are cyclic carboxylic esters, containing a 1-oxacycloalkan-2-one structure (), or analogues having unsaturation or heteroatoms replacing one or more carbon atoms of the ring.
Lactones are formed by intramolecular esterification of the co ...
antiviral
Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses. Unlike most antibiotics, antiviral drugs do no ...
produced by the fungus ''
Penicillium brefeldianum''. Brefeldin A inhibits
protein transport from the
endoplasmic reticulum
The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...
to the
golgi complex
The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles insi ...
indirectly by preventing association of COP-I coat to the Golgi
membrane
A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. B ...
. Brefeldin A was initially isolated with hopes to become an antiviral drug but is now primarily used in research to study protein transport.
History
The compound gets its name from a
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of
anamorph
In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota:
*Teleomorph: the sexual reproductive stage (morph), typically a fruiting body.
*Anamorph: an ase ...
fungus of the ''Penicillium''
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
known as ''Eupenicillium brefeldianum'', though it is found in a variety of species that span several genera. It was first isolated from ''Penicillium decumbens'' in 1958 by V.L. Singleton who initially called it Decumbin.
It was later identified as a metabolite by H.P. Siggs who then went on to identify the chemical structure of the compound in 1971.
Since then several successful
total synthesis
Total synthesis is the complete chemical synthesis of a complex molecule, often a natural product, from simple, commercially-available precursors. It usually refers to a process not involving the aid of biological processes, which distinguishes ...
methods have been described.
Interest in researching brefeldin A was initially lacking due to poor antiviral activity.
However, upon discovery of its mechanism involving disruption of protein transport by Takatsuki and Tamura in 1985 and the
cytotoxic
Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are an immune cell or some types of venom, e.g. from the puff adder (''Bitis arietans'') or brown recluse spider (''Loxosceles reclusa'').
Cell physiology
Treating cells ...
effects observed in certain
cancer cell lines, research efforts were revitalized.
It is currently used solely in research mainly as an assay tool for studying membrane traffic and
vesicle
Vesicle may refer to:
; In cellular biology or chemistry
* Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane
* Synaptic vesicle
; In human embryology
* Vesicle (embryology), bulge-like features o ...
transport dynamics between the endoplasmic reticulum and Golgi apparatus.
Physical properties and storage information
Brefeldin A is found naturally as a white to off-white
crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
line solid. It forms a clear colorless solution when dissolved. It is soluble in
methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
(10 mg/mL),
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
(5 mg/mL),
DMSO
Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula ( CH3)2. This colorless liquid is the sulfoxide most widely used commercially. It is an important polar aprotic solvent that dissolves both polar and nonpolar compounds an ...
(20 mg/mL),
acetone
Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour.
Acetone is miscib ...
, and
ethyl acetate
Ethyl acetate ( systematically ethyl ethanoate, commonly abbreviated EtOAc, ETAC or EA) is the organic compound with the formula , simplified to . This colorless liquid has a characteristic sweet smell (similar to pear drops) and is used in glues ...
(1 mg/mL) without the aid of heating.
It is poorly soluble in water (slightly
miscible
Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). The term is most often applied to liquids but also applies ...
).
It is sold commercially with a purity of 98% or greater.
It is recommended that it be stored desiccate at -20 °C away from direct sunlight.> Its suggested shelf life for use is 6 months as a solid and 1 month as a solution with tightly sealed storage at -20 °C. Since the compound is combustible, contamination with
oxidizing agent
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "Electron acceptor, accepts"/"receives" an electron from a (called the , , or ). In ot ...
s should be avoided to prevent the risk of fire. Direct contact should be avoided as well.
Mechanism of action
![Brefeldin A Inhibition of Intracellular Vesicle Transport](https://upload.wikimedia.org/wikipedia/commons/2/29/Brefeldin_A_Inhibition_of_Intracellular_Vesicle_Transport.png)
In
mammalian
Mammals () are a group of vertebrate animals constituting the class (biology), class Mammalia (), characterized by the presence of mammary glands which in Female#Mammalian female, females produce milk for feeding (nursing) their young, a ...
and
yeast
Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...
cells, the main target of brefeldin A appears to be a
guanine nucleotide exchange factor
Guanine nucleotide exchange factors (GEFs) are proteins or protein domains that activate monomeric GTPases by stimulating the release of guanosine diphosphate (GDP) to allow binding of guanosine triphosphate (GTP). A variety of unrelated structu ...
(GEF) called
GBF1
Golgi-specific brefeldin A-resistance guanine nucleotide exchange factor 1 is a protein that in humans is encoded by the ''GBF1'' gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelia ...
.
[ ] GBF1 is a member of the Arf family of GEFs which are recruited to membranes of the Golgi.
It is responsible for the regulation of
Arf1p GTPase
GTPases are a large family of hydrolase enzymes that bind to the nucleotide guanosine triphosphate (GTP) and hydrolyze it to guanosine diphosphate (GDP). The GTP binding and hydrolysis takes place in the highly conserved P-loop "G domain", a pro ...
.
It does this through converting the inactive GDP-bound form of Arf1p to the active GTP-bound form.
The nucleotide exchange occurs at the catalytic Sec7 domain of GBF1. Activated Arf1p then recruits coat protein β-COP, a subunit of the COP-I complex, to cargo-bound receptors on the membrane.
Coat protein recruitment is necessary for proper vesicle formation and transport. Brefeldin A reversibly inhibits the function of GBF1
uncompetitively by binding to the complex it forms with GDP-bound Arf1p and preventing conversion to the GTP-bound form.
The lack of active Arf1p prevents coat protein recruitment, which then ultimately induces the fusion of neighboring ER and Golgi membranes due to lack of vesicle formation. This is because lack of vesicle formation results in a buildup of
SNARE proteins
SNARE proteins – " SNAP REceptor" – are a large protein family consisting of at least 24 members in yeasts, more than 60 members in mammalian cells,
and some numbers in plants. The primary role of SNARE proteins is to mediate vesicle fu ...
in the Golgi which would otherwise be bound to coat protein-coated vesicles and removed with the vesicles once they bud off.
SNARE proteins mediate membrane fusion and it is postulated that the described SNARE build up in the Golgi increases the chances of aberrant fusion of the Golgi membrane with that of the ER.
The collapse of the Golgi into the ER triggers activation of
unfolded protein response
The unfolded protein response (UPR) is a cellular stress response related to the endoplasmic reticulum (ER) stress. It has been found to be conserved between all mammalian species, as well as yeast and worm organisms.
The UPR is activated in resp ...
(UPR) (or
ER stress)
which can result in
apoptosis
Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes incl ...
.
Toxicity
The toxological effects of brefeldin A have not been studied extensively yet.
Some animal
LD50 values have been reported including 250 mg/kg in mice (interperitoneal) and 275 mg/kg in rats (oral).
Generally, antibiotic
macrolide
The Macrolides are a class of natural products that consist of a large macrocyclic lactone ring to which one or more deoxy sugars, usually cladinose and desosamine, may be attached. The lactone rings are usually 14-, 15-, or 16-membered. Macrol ...
s that share a similar macrocyclic lactone ring to that of brefeldin A have been shown to produce
gastrointestinal
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...
discomfort as the most common side effect.
Some macrolides have been shown to produce
allergic reactions
Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derma ...
and though uncommon this possibility in the case of brefeldin A cannot be disregarded as of yet.
The compound may bind to
hemoglobin
Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...
and inhibit oxygen uptake resulting in
methemoglobinemia
Methemoglobinemia, or methaemoglobinaemia, is a condition of elevated methemoglobin in the blood. Symptoms may include headache, dizziness, shortness of breath, nausea, poor muscle coordination, and blue-colored skin (cyanosis). Complications m ...
, a form of oxygen starvation, though this is not confirmed.
Brefeldin A is not considered to be harmful from direct skin or eye exposure other than transient irritation.
It may cause irritation of the
respiratory system
The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...
if inhaled.
See also
*
Unfolded protein response
The unfolded protein response (UPR) is a cellular stress response related to the endoplasmic reticulum (ER) stress. It has been found to be conserved between all mammalian species, as well as yeast and worm organisms.
The UPR is activated in resp ...
*
Endoplasmic reticulum stress response (ER stress)
References
External links
*
*{{cite journal , vauthors=Nebenführ A, Ritzenthaler C, Robinson DG , title=Brefeldin A: deciphering an enigmatic inhibitor of secretion , journal=Plant Physiol. , volume=130 , issue=3 , pages=1102–8 , date=November 2002 , pmid=12427977 , pmc=1540261 , doi=10.1104/pp.011569
NCI Frederick, Structure and Data for Brefeldin A.(Image)
Macrolide antibiotics
Cell culture reagents
Cyclopentanes