Flavin adenine dinucleotide: Difference between revisions

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FAD can be [[redox|reduced]] to FADH2 through the addition of 2 H+ and 2 e−. FADH2 can also be [[redox|oxidized]] by the loss of 1 H+ and 1 e− to form FADH. The FAD form can be recreated through the further loss of 1 H+ and 1 e−. FAD formation can also occur through the reduction and dehydration of flavin-N(5)-oxide. Based on the oxidation state, flavins take specific colors when in [[aqueous solution]]. [[Amine oxide|flavin-N(5)-oxide]] (superoxidized) is yellow-orange, FAD (fully oxidized) is yellow, FADH (half reduced) is either blue or red based on the [[pH]], and the fully reduced form is colorless. Changing the form can have a large impact on other chemical properties. For example, FAD, the fully oxidized form is subject to [[Nucleophilic substitution|nucleophilic attack]], the fully reduced form, FADH2 has high [[polarizability]], while the half reduced form is unstable in aqueous solution.FAD is an [[aromatic]] ring system, whereas FADH2 is not. This means that FADH2 is significantly higher in energy, without the stabilization through [[resonance]] that the aromatic structure provides. FADH2 is an energy-carrying molecule, because, once oxidized it regains aromaticity and releases the energy represented by this stabilization.

The [[spectroscopy|spectroscopic]] properties of FAD and its variants allows for reaction monitoring by use of [[Ultraviolet-visible spectroscopy|UV-VIS absorption]] and [[Fluorescence spectroscopy|fluorescence]] spectroscopies. Each form of FAD has distinct absorbance spectra, making for easy observation of changes in oxidation state.~~<ref name=DS2 />~~ A major local absorbance maximum for FAD is observed at 450 nm, with an extinction coefficient of 11,300 M−1 cm−1. Flavins in general have fluorescent activity when unbound (proteins bound to flavin nucleic acid derivatives are called [[flavoprotein]]s). This property can be utilized when examining protein binding, observing loss of fluorescent activity when put into the bound state. Oxidized flavins have high absorbances of about 450 nm, and fluoresce at about 515-520 nm.

The [[spectroscopy|spectroscopic]] properties of FAD and its variants allows for reaction monitoring by use of [[Ultraviolet-visible spectroscopy|UV-VIS absorption]] and [[Fluorescence spectroscopy|fluorescence]] spectroscopies. Each form of FAD has distinct absorbance spectra, making for easy observation of changes in oxidation state. A major local absorbance maximum for FAD is observed at 450 nm, with an extinction coefficient of 11,300 M−1 cm−1. Flavins in general have fluorescent activity when unbound (proteins bound to flavin nucleic acid derivatives are called [[flavoprotein]]s). This property can be utilized when examining protein binding, observing loss of fluorescent activity when put into the bound state. Oxidized flavins have high absorbances of about 450 nm, and fluoresce at about 515-520 nm.

== Chemical states ==

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== Biosynthesis ==

FAD plays a major role as an enzyme [[Cofactor (biochemistry)|cofactor]] along with [[flavin mononucleotide]], another molecule originating from riboflavin. Bacteria, fungi and plants can produce [[riboflavin]], but other [[eukaryote]]s, such as humans, have lost the ability to make it. Therefore, humans must obtain riboflavin, also known as vitamin B2, from dietary sources. Riboflavin is generally ingested in the small intestine and then transported to cells via carrier proteins. [[Riboflavin kinase]] (EC 2.7.1.26) adds a phosphate group to riboflavin to produce flavin mononucleotide, and then [[FMN adenylyltransferase|FAD synthetase]] attaches an adenine [[nucleotide]]; both steps require [[adenosine triphosphate|ATP]].~~<ref name="Ref 3" />~~ Bacteria generally have one bi-functional enzyme, but [[archaea]] and eukaryotes usually employ two distinct enzymes. Current research indicates that distinct [[protein isoforms|isoforms]] exist in the [[cytosol]] and [[mitochondrion|mitochondria]]. It seems that FAD is synthesized in both locations and potentially transported where needed.

FAD plays a major role as an enzyme [[Cofactor (biochemistry)|cofactor]] along with [[flavin mononucleotide]], another molecule originating from riboflavin. Bacteria, fungi and plants can produce [[riboflavin]], but other [[eukaryote]]s, such as humans, have lost the ability to make it. Therefore, humans must obtain riboflavin, also known as vitamin B2, from dietary sources. Riboflavin is generally ingested in the small intestine and then transported to cells via carrier proteins. [[Riboflavin kinase]] (EC 2.7.1.26) adds a phosphate group to riboflavin to produce flavin mononucleotide, and then [[FMN adenylyltransferase|FAD synthetase]] attaches an adenine [[nucleotide]]; both steps require [[adenosine triphosphate|ATP]]. Bacteria generally have one bi-functional enzyme, but [[archaea]] and eukaryotes usually employ two distinct enzymes. Current research indicates that distinct [[protein isoforms|isoforms]] exist in the [[cytosol]] and [[mitochondrion|mitochondria]]. It seems that FAD is synthesized in both locations and potentially transported where needed.

:[[Image:FAD Synthesis.png|250px]]

Line 146:

[[Cytochrome P450]] type enzymes that catalyze monooxygenase (hydroxylation) reactions are dependent on the transfer of two electrons from FAD to the P450. Two types of P450 systems are found in eukaryotes. The P450 systems that are located in the endoplasmic reticulum are dependent on a [[cytochrome P-450 reductase]] (CPR) that contains both an FAD and an [[Flavin mononucleotide|FMN]]. The two electrons on reduced FAD (FADH2) are transferred one at a time to FMN and then a single electron is passed from FMN to the heme of the P450.

The P450 systems that are located in the mitochondria are dependent on two electron transfer proteins: An FAD containing [[adrenodoxin reductase]] (AR) and a small iron-sulfur group containing protein named [[adrenodoxin]]. FAD is embedded in the FAD-binding domain of AR. The FAD of AR is reduced to FADH2 by transfer of two electrons from NADPH that binds in the NADP-binding domain of AR. The structure of this enzyme is highly conserved to maintain precisely the alignment of electron donor NADPH and acceptor FAD for efficient electron transfer.~~<ref name="2017-Hanukoglu-JME" />~~ The two electrons in reduced FAD are transferred one a time to adrenodoxin which in turn donates the single electron to the heme group of the mitochondrial P450.

The P450 systems that are located in the mitochondria are dependent on two electron transfer proteins: An FAD containing [[adrenodoxin reductase]] (AR) and a small iron-sulfur group containing protein named [[adrenodoxin]]. FAD is embedded in the FAD-binding domain of AR. The FAD of AR is reduced to FADH2 by transfer of two electrons from NADPH that binds in the NADP-binding domain of AR. The structure of this enzyme is highly conserved to maintain precisely the alignment of electron donor NADPH and acceptor FAD for efficient electron transfer. The two electrons in reduced FAD are transferred one a time to adrenodoxin which in turn donates the single electron to the heme group of the mitochondrial P450.

The structures of the reductase of the microsomal versus reductase of the mitochondrial P450 systems are completely different and show no homology.

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=== Drug design ===

New [[drug design|design]] of anti-bacterial medications is of continuing importance in scientific research as bacterial antibiotic resistance to common antibiotics increases. A specific metabolic protein that uses FAD ([[succinate dehydrogenase|Complex II]]) is vital for bacterial virulence, and so targeting FAD synthesis or creating FAD analogs could be a useful area of investigation. Already, scientists have determined the two structures FAD usually assumes once bound: either an extended or a butterfly conformation, in which the molecule essentially folds in half, resulting in the stacking of the adenine and isoalloxazine rings. FAD imitators that are able to bind in a similar manner but do not permit protein function could be useful mechanisms of inhibiting bacterial infection.~~<ref name="GC2"/>~~ Alternatively, drugs blocking FAD synthesis could achieve the same goal; this is especially intriguing because human and bacterial FAD synthesis relies on very different enzymes, meaning that a drug made to target bacterial FAD synthase would be unlikely to interfere with the human FAD synthase enzymes.

New [[drug design|design]] of anti-bacterial medications is of continuing importance in scientific research as bacterial antibiotic resistance to common antibiotics increases. A specific metabolic protein that uses FAD ([[succinate dehydrogenase|Complex II]]) is vital for bacterial virulence, and so targeting FAD synthesis or creating FAD analogs could be a useful area of investigation. Already, scientists have determined the two structures FAD usually assumes once bound: either an extended or a butterfly conformation, in which the molecule essentially folds in half, resulting in the stacking of the adenine and isoalloxazine rings. FAD imitators that are able to bind in a similar manner but do not permit protein function could be useful mechanisms of inhibiting bacterial infection. Alternatively, drugs blocking FAD synthesis could achieve the same goal; this is especially intriguing because human and bacterial FAD synthesis relies on very different enzymes, meaning that a drug made to target bacterial FAD synthase would be unlikely to interfere with the human FAD synthase enzymes.

=== Optogenetics ===

[[Optogenetics]] allows control of biological events in a non-invasive manner. The field has advanced in recent years with a number of new tools, including those to trigger light sensitivity, such as the Blue-Light-Utilizing FAD domains (BLUF). BLUFs encode a 100 to 140 [[amino acid]] sequence that was derived from photoreceptors in plants and bacteria.~~<ref name="GK15"/>~~ Similar to other [[photoreceptor protein|photoreceptors]], the light causes structural changes in the BLUF domain that results in disruption of downstream interactions. Current research investigates proteins with the appended BLUF domain and how different external factors can impact the proteins.

[[Optogenetics]] allows control of biological events in a non-invasive manner. The field has advanced in recent years with a number of new tools, including those to trigger light sensitivity, such as the Blue-Light-Utilizing FAD domains (BLUF). BLUFs encode a 100 to 140 [[amino acid]] sequence that was derived from photoreceptors in plants and bacteria. Similar to other [[photoreceptor protein|photoreceptors]], the light causes structural changes in the BLUF domain that results in disruption of downstream interactions. Current research investigates proteins with the appended BLUF domain and how different external factors can impact the proteins.

=== Treatment monitoring ===

@@ Line 68: / Line 68: @@
 FAD can be [[redox|reduced]] to FADH<sub>2</sub> through the addition of 2 H<sup>+</sup> and 2 e<sup>−</sup>. FADH<sub>2</sub> can also be [[redox|oxidized]] by the loss of 1 H<sup>+</sup> and 1 e<sup>−</sup> to form FADH. The FAD form can be recreated through the further loss of 1 H<sup>+</sup> and 1 e<sup>−</sup>. FAD formation can also occur through the reduction and dehydration of flavin-N(5)-oxide. Based on the oxidation state, flavins take specific colors when in [[aqueous solution]].  [[Amine oxide|flavin-N(5)-oxide]] (superoxidized) is yellow-orange, FAD (fully oxidized) is yellow, FADH (half reduced) is either blue or red based on the [[pH]], and the fully reduced form is colorless. Changing the form can have a large impact on other chemical properties. For example, FAD, the fully oxidized form is subject to [[Nucleophilic substitution|nucleophilic attack]], the fully reduced form,  FADH<sub>2</sub> has high [[polarizability]], while the half reduced form is unstable in aqueous solution.FAD is an [[aromatic]] ring system, whereas FADH<sub>2</sub> is not. This means that FADH<sub>2</sub> is significantly higher in energy, without the stabilization through [[resonance]] that the aromatic structure provides.  FADH<sub>2</sub> is an energy-carrying molecule, because, once oxidized it regains aromaticity and releases the energy represented by this stabilization.
-The [[spectroscopy|spectroscopic]] properties of FAD and its variants allows for reaction monitoring by use of [[Ultraviolet-visible spectroscopy|UV-VIS absorption]] and [[Fluorescence spectroscopy|fluorescence]] spectroscopies. Each form of FAD has distinct absorbance spectra, making for easy observation of changes in oxidation state.<ref name=DS2 /> A major local absorbance maximum for FAD is observed at 450&nbsp;nm, with an extinction coefficient of 11,300 M<sup>−1</sup> cm<sup>−1</sup>. Flavins in general have fluorescent activity when unbound (proteins bound to flavin nucleic acid derivatives are called [[flavoprotein]]s). This property can be utilized when examining protein binding, observing loss of fluorescent activity when put into the bound state. Oxidized flavins have high absorbances of about 450&nbsp;nm, and fluoresce at about 515-520&nbsp;nm.
+The [[spectroscopy|spectroscopic]] properties of FAD and its variants allows for reaction monitoring by use of [[Ultraviolet-visible spectroscopy|UV-VIS absorption]] and [[Fluorescence spectroscopy|fluorescence]] spectroscopies. Each form of FAD has distinct absorbance spectra, making for easy observation of changes in oxidation state. A major local absorbance maximum for FAD is observed at 450&nbsp;nm, with an extinction coefficient of 11,300 M<sup>−1</sup> cm<sup>−1</sup>. Flavins in general have fluorescent activity when unbound (proteins bound to flavin nucleic acid derivatives are called [[flavoprotein]]s). This property can be utilized when examining protein binding, observing loss of fluorescent activity when put into the bound state. Oxidized flavins have high absorbances of about 450&nbsp;nm, and fluoresce at about 515-520&nbsp;nm.
 == Chemical states ==
@@ Line 94: / Line 94: @@
 == Biosynthesis ==
-FAD plays a major role as an enzyme [[Cofactor (biochemistry)|cofactor]] along with [[flavin mononucleotide]], another molecule originating from riboflavin. Bacteria, fungi and plants can produce [[riboflavin]], but other [[eukaryote]]s, such as humans, have lost the ability to make it. Therefore, humans must obtain riboflavin, also known as vitamin B2, from dietary sources. Riboflavin is generally ingested in the small intestine and then transported to cells via carrier proteins. [[Riboflavin kinase]] (EC 2.7.1.26) adds a phosphate group to riboflavin to produce flavin mononucleotide, and then [[FMN adenylyltransferase|FAD synthetase]] attaches an adenine [[nucleotide]]; both steps require [[adenosine triphosphate|ATP]].<ref name="Ref 3" /> Bacteria generally have one bi-functional enzyme, but [[archaea]] and eukaryotes usually employ two distinct enzymes. Current research indicates that distinct [[protein isoforms|isoforms]] exist in the [[cytosol]] and [[mitochondrion|mitochondria]]. It seems that FAD is synthesized in both locations and potentially transported where needed.
+FAD plays a major role as an enzyme [[Cofactor (biochemistry)|cofactor]] along with [[flavin mononucleotide]], another molecule originating from riboflavin. Bacteria, fungi and plants can produce [[riboflavin]], but other [[eukaryote]]s, such as humans, have lost the ability to make it. Therefore, humans must obtain riboflavin, also known as vitamin B2, from dietary sources. Riboflavin is generally ingested in the small intestine and then transported to cells via carrier proteins. [[Riboflavin kinase]] (EC 2.7.1.26) adds a phosphate group to riboflavin to produce flavin mononucleotide, and then [[FMN adenylyltransferase|FAD synthetase]] attaches an adenine [[nucleotide]]; both steps require [[adenosine triphosphate|ATP]]. Bacteria generally have one bi-functional enzyme, but [[archaea]] and eukaryotes usually employ two distinct enzymes. Current research indicates that distinct [[protein isoforms|isoforms]] exist in the [[cytosol]] and [[mitochondrion|mitochondria]]. It seems that FAD is synthesized in both locations and potentially transported where needed.
 :[[Image:FAD Synthesis.png|250px]]
@@ Line 146: / Line 146: @@
 [[Cytochrome P450]] type enzymes that catalyze monooxygenase (hydroxylation) reactions are dependent on the transfer of two electrons from FAD to the P450. Two types of P450 systems are found in eukaryotes. The P450 systems that are located in the endoplasmic reticulum are dependent on a [[cytochrome P-450 reductase]] (CPR) that contains both an FAD and an [[Flavin mononucleotide|FMN]]. The two electrons on reduced FAD (FADH<sub>2</sub>) are transferred one at a time to FMN and then a single electron is passed from FMN to the heme of the P450.
-The P450 systems that are located in the mitochondria are dependent on two electron transfer proteins: An FAD containing [[adrenodoxin reductase]] (AR) and a small iron-sulfur group containing protein named [[adrenodoxin]]. FAD is embedded in the FAD-binding domain of AR. The FAD of AR is reduced to FADH<sub>2</sub> by transfer of two electrons from NADPH that binds in the NADP-binding domain of AR. The structure of this enzyme is highly conserved to maintain precisely the alignment of electron donor NADPH and acceptor FAD for efficient electron transfer.<ref name="2017-Hanukoglu-JME" /> The two electrons in reduced FAD are transferred one a time to adrenodoxin which in turn donates the single electron to the heme group of the mitochondrial P450.
+The P450 systems that are located in the mitochondria are dependent on two electron transfer proteins: An FAD containing [[adrenodoxin reductase]] (AR) and a small iron-sulfur group containing protein named [[adrenodoxin]]. FAD is embedded in the FAD-binding domain of AR. The FAD of AR is reduced to FADH<sub>2</sub> by transfer of two electrons from NADPH that binds in the NADP-binding domain of AR. The structure of this enzyme is highly conserved to maintain precisely the alignment of electron donor NADPH and acceptor FAD for efficient electron transfer. The two electrons in reduced FAD are transferred one a time to adrenodoxin which in turn donates the single electron to the heme group of the mitochondrial P450.
 The structures of the reductase of the microsomal versus reductase of the mitochondrial P450 systems are completely different and show no homology.
@@ Line 174: / Line 174: @@
 === Drug design ===
-New [[drug design|design]] of anti-bacterial medications is of continuing importance in scientific research as bacterial antibiotic resistance to common antibiotics increases.  A specific metabolic protein that uses FAD ([[succinate dehydrogenase|Complex II]]) is vital for bacterial virulence, and so targeting FAD synthesis or creating FAD analogs could be a useful area of investigation. Already, scientists have determined the two structures FAD usually assumes once bound: either an extended or a butterfly conformation, in which the molecule essentially folds in half, resulting in the stacking of the adenine and isoalloxazine rings.  FAD imitators that are able to bind in a similar manner but do not permit protein function could be useful mechanisms of inhibiting bacterial infection.<ref name="GC2"/>  Alternatively, drugs blocking FAD synthesis could achieve the same goal; this is especially intriguing because human and bacterial FAD synthesis relies on very different enzymes, meaning that a drug made to target bacterial FAD synthase would be unlikely to interfere with the human FAD synthase enzymes.
+New [[drug design|design]] of anti-bacterial medications is of continuing importance in scientific research as bacterial antibiotic resistance to common antibiotics increases.  A specific metabolic protein that uses FAD ([[succinate dehydrogenase|Complex II]]) is vital for bacterial virulence, and so targeting FAD synthesis or creating FAD analogs could be a useful area of investigation. Already, scientists have determined the two structures FAD usually assumes once bound: either an extended or a butterfly conformation, in which the molecule essentially folds in half, resulting in the stacking of the adenine and isoalloxazine rings.  FAD imitators that are able to bind in a similar manner but do not permit protein function could be useful mechanisms of inhibiting bacterial infection. Alternatively, drugs blocking FAD synthesis could achieve the same goal; this is especially intriguing because human and bacterial FAD synthesis relies on very different enzymes, meaning that a drug made to target bacterial FAD synthase would be unlikely to interfere with the human FAD synthase enzymes.
 === Optogenetics ===
-[[Optogenetics]] allows control of biological events in a non-invasive manner.  The field has advanced in recent years with a number of new tools, including those to trigger light sensitivity, such as the Blue-Light-Utilizing FAD domains (BLUF).  BLUFs encode a 100 to 140 [[amino acid]] sequence that was derived from photoreceptors in plants and bacteria.<ref name="GK15"/>  Similar to other [[photoreceptor protein|photoreceptors]], the light causes structural changes in the BLUF domain that results in disruption of downstream interactions. Current research investigates proteins with the appended BLUF domain and how different external factors can impact the proteins.
+[[Optogenetics]] allows control of biological events in a non-invasive manner.  The field has advanced in recent years with a number of new tools, including those to trigger light sensitivity, such as the Blue-Light-Utilizing FAD domains (BLUF).  BLUFs encode a 100 to 140 [[amino acid]] sequence that was derived from photoreceptors in plants and bacteria. Similar to other [[photoreceptor protein|photoreceptors]], the light causes structural changes in the BLUF domain that results in disruption of downstream interactions. Current research investigates proteins with the appended BLUF domain and how different external factors can impact the proteins.
 === Treatment monitoring ===