Sulfur metabolism
Encyclopedia
Sulfur metabolism is vital for all living organism
s as it is a constituent of a number of essential organic molecules like cysteine
, methionine
, coenzyme A
, and iron-sulfur cluster
s. These compounds are involved in a number of essential cellular processes such as protein biosynthesis or the transfer of electrons and acyl groups. Sulfur, therefore, is an essential component of all living cells. The importance of sulfur is well-represented by the sulfhydryl (thiol
) functional group, lying at the centre of many chemical reactions in biology. Thiol-based reactions have diverse biological functions: thiols in thioredoxin
s provide reductive power for the synthesis of biological molecules; thiols in coenzyme A facilitate the oxidation of pyruvate
and fatty acid
s to generate energy for living cells; and thiols in glutathione
and mycothiol
are involved in detoxifying hazardous molecules, as well as maintaining the redox
balance of living cells. Additionally, sulfur containing molecules function as messengers in intracellular and intra-species communication. Sulfur is also a constituent of many other biomolecules like cysteine, methionine, biotin
, lipoic acid
, molybdopterin
, thionucleosides in tRNAs, and thiamine
.
, such as mycobacteria
, hold importance both for its biological implications as well as discovering drug targets against enzymes in these pathways. In recent times, the endeavour to map the sulfur metabolic pathways has been greatly facilitated by the emerging information drawn from genome sequencing.
. The other mycobacterial species are Mycobacterium leprae
, which causes leprosy
in humans, Mycobacterium bovis
which causes tuberculosis
in cattle, Mycobacterium avium which causes disease in immunocompromised individuals' M. bovis bacille Calmette–Guérin (BCG), which is an attenuated strain of M. bovis used as a vaccine strain, and Mycobacterium smegmatis
, which is a saprophytic non-pathogenic species used extensively as a laboratory model for mycobacterial research.
s and, due to their scarcity in many foods and feeds, their biosynthesis is of great industrial interest. Therefore, the metabolism of sulfur in Corynebacterium glutamicum has been studied. Besides the pathways to obtain and utilize sulfur from the environment, the reactions leading to and from the sulfur-containing amino acids cysteine and methionine have been analyzed in great detail, revealing a number of so far unique metabolic routes. In addition, the regulation of sulfur metabolism has been analyzed on the transcriptional as well as on the enzymatic level, revealing the presence of at least three transcriptional regulators and a high number of feed-back inhibitions of key enzymes.
is a species of bacterium that can become an opportunistic pathogen in the mixed microflora that colonizes the space between the teeth and inflamed gingival tissues (periodontal pocket). The generation of volatile sulfur-containing compounds from amino acid metabolism by the enzyme cystalysin is cytotoxic and may be considered one of the virulence determinants of T. denticola.
contain many unique redox enzymes possibly because of the wide range of strategies they employ for energy conversion, the many extreme environments they inhabit, and the evolutionary separation of the archaea from bacteria that catalyze similar reactions. Sulfur metabolism is the subject of much research in archaea, including both sulfur oxidation and reduction and the hydrogenase
s frequently associated with sulfur reduction.
to make sulfur-containing organic compounds. Fungi have a sulfate assimilation pathway which transports sulfate into the cell, activates it with ATP and reduces it to sulfide
which is a direct precursor of cysteine. When cysteine or methionine is available in the environment, the energy-consuming sulfate assimilation pathway is shut off by the sulfur metabolite repression system as sulfate assimilation is not required. All fungi have the same sulfate assimilation pathway but fungi differ in the organisation of sulfur amino acids metabolism and some species have alternative pathways of cysteine synthesis. All fungi can synthesize methionine from cysteine but only some can metabolize methionine to cysteine.
varying between plant species. Sulfate taken up by the roots is the major source for growth; it is reduced to sulfide and then can be metabolized further and incorporated into cysteine. Cysteine is the precursor of most other organic sulfur compounds in plants.
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s as it is a constituent of a number of essential organic molecules like cysteine
Cysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
, methionine
Methionine
Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar. This amino-acid is coded by the codon AUG, also known as the initiation codon, since it indicates mRNA's coding region where translation into protein...
, coenzyme A
Coenzyme A
Coenzyme A is a coenzyme, notable for its role in the synthesis and oxidation of fatty acids, and the oxidation of pyruvate in the citric acid cycle. All sequenced genomes encode enzymes that use coenzyme A as a substrate, and around 4% of cellular enzymes use it as a substrate...
, and iron-sulfur cluster
Iron-sulfur cluster
For biological Fe-S clusters, see iron-sulfur proteins.Iron-sulfur clusters are ensembles of iron and sulfide centres. Fe-S clusters are most often discussed in the context of the biological role for iron-sulfur proteins. Many Fe-S clusters are known in the area of organometallic chemistry and as...
s. These compounds are involved in a number of essential cellular processes such as protein biosynthesis or the transfer of electrons and acyl groups. Sulfur, therefore, is an essential component of all living cells. The importance of sulfur is well-represented by the sulfhydryl (thiol
Thiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...
) functional group, lying at the centre of many chemical reactions in biology. Thiol-based reactions have diverse biological functions: thiols in thioredoxin
Thioredoxin
Thioredoxin is a class of small redox proteins known to be present in all organisms. It plays a role in many important biological processes. In humans, it is encoded by the TXN gene. Loss-of-function mutation of either of the two human thioredoxin genes is lethal at the four-cell stage of the...
s provide reductive power for the synthesis of biological molecules; thiols in coenzyme A facilitate the oxidation of pyruvate
Pyruvic acid
Pyruvic acid is an organic acid, a ketone, as well as the simplest of the alpha-keto acids. The carboxylate ion of pyruvic acid, CH3COCOO−, is known as pyruvate, and is a key intersection in several metabolic pathways....
and fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s to generate energy for living cells; and thiols in glutathione
Glutathione
Glutathione is a tripeptide that contains an unusual peptide linkage between the amine group of cysteine and the carboxyl group of the glutamate side-chain...
and mycothiol
Mycothiol
Mycothiol is an unusual thiol compound found in the Actinobacteria. It is composed of a cysteine residue with an acetylated amino group linked to glucosamine, which is then linked to inositol. The oxidized, disulfide form of mycothiol is called mycothione, and is reduced to mycothiol by the...
are involved in detoxifying hazardous molecules, as well as maintaining the redox
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
balance of living cells. Additionally, sulfur containing molecules function as messengers in intracellular and intra-species communication. Sulfur is also a constituent of many other biomolecules like cysteine, methionine, biotin
Biotin
Biotin, also known as Vitamin H or Coenzyme R, is a water-soluble B-complex vitamin discovered by Bateman in 1916. It is composed of a ureido ring fused with a tetrahydrothiophene ring. A valeric acid substituent is attached to one of the carbon atoms of the tetrahydrothiophene ring...
, lipoic acid
Lipoic acid
Lipoic acid , also known as α-lipoic acid and Alpha Lipoic Acid is an organosulfur compound derived from octanoic acid. LA contains two vicinal sulfur atoms attached via a disulfide bond and is thus considered to be oxidized...
, molybdopterin
Molybdopterin
Molybdopterins, when reacted with molybdenum or tungsten in the form of molybdate or tungstate, are a class of cofactors found in most molybdenum and all tungsten enzymes...
, thionucleosides in tRNAs, and thiamine
Thiamine
Thiamine or thiamin or vitamin B1 , named as the "thio-vitamine" is a water-soluble vitamin of the B complex. First named aneurin for the detrimental neurological effects if not present in the diet, it was eventually assigned the generic descriptor name vitamin B1. Its phosphate derivatives are...
.
Bacteria
Sulfur metabolic pathways of pathogenic bacteriaBacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, such as mycobacteria
Mycobacterium
Mycobacterium is a genus of Actinobacteria, given its own family, the Mycobacteriaceae. The genus includes pathogens known to cause serious diseases in mammals, including tuberculosis and leprosy...
, hold importance both for its biological implications as well as discovering drug targets against enzymes in these pathways. In recent times, the endeavour to map the sulfur metabolic pathways has been greatly facilitated by the emerging information drawn from genome sequencing.
Mycobacterium
Sulfur metabolism in mycobacteria plays a role in the pathogenesis of the insidious human pathogen, Mycobacterium tuberculosisMycobacterium tuberculosis
Mycobacterium tuberculosis is a pathogenic bacterial species in the genus Mycobacterium and the causative agent of most cases of tuberculosis . First discovered in 1882 by Robert Koch, M...
. The other mycobacterial species are Mycobacterium leprae
Mycobacterium leprae
Mycobacterium leprae, also known as Hansen’s coccus spirilly, mostly found in warm tropical countries, is a bacterium that causes leprosy . It is an intracellular, pleomorphic, acid-fast bacterium. M. leprae is an aerobic bacillus surrounded by the characteristic waxy coating unique to mycobacteria...
, which causes leprosy
Leprosy
Leprosy or Hansen's disease is a chronic disease caused by the bacteria Mycobacterium leprae and Mycobacterium lepromatosis. Named after physician Gerhard Armauer Hansen, leprosy is primarily a granulomatous disease of the peripheral nerves and mucosa of the upper respiratory tract; skin lesions...
in humans, Mycobacterium bovis
Mycobacterium bovis
Mycobacterium bovis is a slow-growing , aerobic bacterium and the causative agent of tuberculosis in cattle...
which causes tuberculosis
Tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...
in cattle, Mycobacterium avium which causes disease in immunocompromised individuals' M. bovis bacille Calmette–Guérin (BCG), which is an attenuated strain of M. bovis used as a vaccine strain, and Mycobacterium smegmatis
Mycobacterium smegmatis
Mycobacterium smegmatis is 3.0 to 5.0 µm long with a bacillus shape, an acid-fast bacterial species in the phylum Actinobacteria. It can be stained by Ziehl-Neelsen method and the auramine-rhodamine fluorescent method. It was first reported in November 1884 by Lustgarten, who found a bacillus...
, which is a saprophytic non-pathogenic species used extensively as a laboratory model for mycobacterial research.
Corynebacterium
An external supply of sulfur-containing compounds is essential for many eukaryoteEukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
s and, due to their scarcity in many foods and feeds, their biosynthesis is of great industrial interest. Therefore, the metabolism of sulfur in Corynebacterium glutamicum has been studied. Besides the pathways to obtain and utilize sulfur from the environment, the reactions leading to and from the sulfur-containing amino acids cysteine and methionine have been analyzed in great detail, revealing a number of so far unique metabolic routes. In addition, the regulation of sulfur metabolism has been analyzed on the transcriptional as well as on the enzymatic level, revealing the presence of at least three transcriptional regulators and a high number of feed-back inhibitions of key enzymes.
Treponema
Treponema denticolaTreponema denticola
Treponema denticola is a motile and highly proteolytic bacterium. The Gram-negative oral spirochete is associated with the incidence and severity of human periodontal disease. Treponema denticola levels in the mouth are elevated in patients with periodontal diseases and the species is considered...
is a species of bacterium that can become an opportunistic pathogen in the mixed microflora that colonizes the space between the teeth and inflamed gingival tissues (periodontal pocket). The generation of volatile sulfur-containing compounds from amino acid metabolism by the enzyme cystalysin is cytotoxic and may be considered one of the virulence determinants of T. denticola.
Archaea
One of the hallmarks of living systems is their ability to use favorable redox reactions in the conversion of energy to forms that are useful to the cell. Microbes in the domain ArchaeaArchaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
contain many unique redox enzymes possibly because of the wide range of strategies they employ for energy conversion, the many extreme environments they inhabit, and the evolutionary separation of the archaea from bacteria that catalyze similar reactions. Sulfur metabolism is the subject of much research in archaea, including both sulfur oxidation and reduction and the hydrogenase
Hydrogenase
A hydrogenase is an enzyme that catalyses the reversible oxidation of molecular hydrogen . Hydrogenases play a vital role in anaerobic metabolism....
s frequently associated with sulfur reduction.
Fungi
Fungi metabolize inorganic sulfateSulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
to make sulfur-containing organic compounds. Fungi have a sulfate assimilation pathway which transports sulfate into the cell, activates it with ATP and reduces it to sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
which is a direct precursor of cysteine. When cysteine or methionine is available in the environment, the energy-consuming sulfate assimilation pathway is shut off by the sulfur metabolite repression system as sulfate assimilation is not required. All fungi have the same sulfate assimilation pathway but fungi differ in the organisation of sulfur amino acids metabolism and some species have alternative pathways of cysteine synthesis. All fungi can synthesize methionine from cysteine but only some can metabolize methionine to cysteine.
Plants
Sulfur is an essential element for the growth and physiology of plants with sulfur assimilationSulfur assimilation
Sulfur is an essential element for growth and physiological functioning of plants. However, its content strongly varies between plant species and it ranges from 0.1 to 6 % of the plants' dry weight. Sulfates taken up by the roots are the major sulfur source for growth, though it has to be reduced...
varying between plant species. Sulfate taken up by the roots is the major source for growth; it is reduced to sulfide and then can be metabolized further and incorporated into cysteine. Cysteine is the precursor of most other organic sulfur compounds in plants.
External links
- http://www.sulfur-research.de/
- https://swww2.le.ac.uk:8443/uol/ebulletin/publications/2000-2009/2008/12/npfolder.2008-12-19.9734606566/nparticle.2008-12-22.2553167374