Correlación estructural entre las encefalinas y la morfina

Opioid peptides are

peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A ...

s that bind to

opioid receptor Opioid receptors are a group of inhibitory G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nociceptin. The opioid receptors are ~40% identical to somatostatin ...

s in the brain;

opiate An opiate, in classical pharmacology, is a substance derived from opium. In more modern usage, the term ''opioid'' is used to designate all substances, both natural and synthetic, that bind to opioid receptors in the brain (including antagonis ...

s and

opioid Opioids are substances that act on opioid receptors to produce morphine-like effects. Medically they are primarily used for pain relief, including anesthesia. Other medical uses include suppression of diarrhea, replacement therapy for opioid us ...

s mimic the effect of these peptides. Such peptides may be produced by the body itself, for example

endorphin Endorphins (contracted from endogenous morphine) are chemical signals in the brain that block the perception of pain and increase feelings of wellbeing. They are produced and stored in an area of the brain known as the pituitary gland. Hist ...

s. The effects of these peptides vary, but they all resemble those of opiates. Brain opioid peptide systems are known to play an important role in

motivation Motivation is the reason for which humans and other animals initiate, continue, or terminate a behavior at a given time. Motivational states are commonly understood as forces acting within the agent that create a disposition to engage in goal-dire ...

emotion Emotions are mental states brought on by neurophysiological changes, variously associated with thoughts, feelings, behavioral responses, and a degree of pleasure or displeasure. There is currently no scientific consensus on a definition. ...

, attachment behaviour, the response to

stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...

and

pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...

, control of food intake, and the rewarding effects of

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

and

nicotine Nicotine is a natural product, naturally produced alkaloid in the nightshade family of plants (most predominantly in tobacco and ''Duboisia hopwoodii'') and is widely used recreational drug use, recreationally as a stimulant and anxiolytic. As ...

. Opioid-like peptides may also be absorbed from partially digested

food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is inge ...

(

casomorphin Casomorphin is an opioid peptide (protein fragment) derived from the digestion of the milk protein casein. Health Digestive enzymes can break casein down into peptides that have some biological activity in cells and in laboratory animals though ...

s, exorphins, and

rubiscolin The rubiscolins are a group of opioid peptides that are formed during digestion of the ribulose bisphosphate carboxylase/oxygenase (Rubisco) protein from spinach leaves. These peptides have much in common with the better-known gluten exorphin Glu ...

s). The

opioid food peptides Opioid food peptides include: * Casomorphin (from milk) * Gluten exorphin (from gluten) * Gliadorphin/gluteomorphin (from gluten) * Rubiscolin (from spinach) * Soymorphin-5 (from soy) * Oryzatensin (from rice Rice is the seed of the grass ...

have lengths of typically 4–8

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

s. The body's own opioids are generally much longer. Opioid peptides are released by

post-translational Post-translational modification (PTM) is the covalent and generally enzymatic modification of proteins following protein biosynthesis. This process occurs in the endoplasmic reticulum and the golgi apparatus. Proteins are synthesized by ribosom ...

proteolytic cleavage Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Uncatalysed, the hydrolysis of peptide bonds is extremely slow, taking hundreds of years. Proteolysis is typically catalysed by cellular enzymes called proteases, ...

precursor protein A protein precursor, also called a pro-protein or pro-peptide, is an inactive protein (or peptide) that can be turned into an active form by post-translational modification, such as breaking off a piece of the molecule or adding on another molecule ...

s. The precursors consist of the following components: a signal sequence that precedes a conserved region of about 50 residues; a variable-length region; and the sequence of the

neuropeptides Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like the ...

themselves.

Sequence In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is calle ...

analysis reveals that the conserved

N-terminal The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the ami ...

region of the precursors contains 6

cysteine Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, sometime ...

s, which are probably involved in

disulfide bond In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...

formation. It is speculated that this region might be important for neuropeptide processing.

Endogenous

The human

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

contains several homologous

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 ...

s that are known to

code In communications and information processing, code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form, sometimes shortened or secret, for communication through a communication ...

for endogenous opioid peptides. *The nucleotide sequence of the human gene for

proopiomelanocortin Pro-opiomelanocortin (POMC) is a precursor polypeptide with 241 amino acid residues. POMC is synthesized in corticotrophs of the anterior pituitary from the 267-amino-acid-long polypeptide precursor pre-pro-opiomelanocortin (pre-POMC), by the r ...

(POMC) was characterized in 1980. The POMC gene codes for endogenous opioids such as

β-endorphin ''beta''-Endorphin (β-endorphin) is an endogenous opioid neuropeptide and peptide hormone that is produced in certain neurons within the central nervous system and peripheral nervous system. It is one of three endorphins that are produced in ...

and

γ-endorphin γ-Endorphin (''gamma''-endorphin) is an opioid peptide that is characterized by the presence of 17 amino acids. The first 16 amino acids are identical to α-endorphin; leucine added at the end. In addition, γ-endorphin is identical to the fir ...

. *The human gene for the

enkephalin An enkephalin is a pentapeptide involved in regulating nociception in the body. The enkephalins are termed endogenous ligands, as they are internally derived and bind to the body's opioid receptors. Discovered in 1975, two forms of enkephalin ...

s was isolated and its sequence described in 1982. *The human gene for

dynorphin Dynorphins (Dyn) are a class of opioid peptides that arise from the precursor protein prodynorphin. When prodynorphin is cleaved during processing by proprotein convertase 2 (PC2), multiple active peptides are released: dynorphin A, dynorphin B, a ...

s (originally called the "Enkephalin B" gene because of sequence similarity to the enkephalin gene) was isolated and its sequence described in 1983. *The PNOC gene encoding prepronociceptin, which is cleaved into nociceptin and potentially two additional neuropeptides. *

Adrenorphin Adrenorphin, also sometimes referred to as metorphamide, is an endogenous, C-terminally amidated, opioid octapeptide (Tyr-Gly-Gly-Phe-Met-Arg-Arg-Val-NH2, YGGFMRRV-NH2) that is produced from proteolytic cleavage of proenkephalin A and is wid ...

, amidorphin, and

leumorphin Leumorphin, also known as dynorphin B1–29, is a naturally occurring endogenous opioid peptide. Derived as a proteolytic cleavage product of residues 226-254 of prodynorphin (preproenkephalin B), leumorphin is a nonacosapeptide (29 amino acid ...

were discovered in the 1980s. *The

endomorphin Endomorphins are considered to be natural opioid neurotransmitters central to pain relief. The two known endomorphins, endomorphin-1 and endomorphin-2, are tetrapeptides, consisting of Tyr-Pro-Trp-Phe and Tyr-Pro-Phe-Phe amino acid sequences resp ...

s were discovered in the 1990s. *

Opiorphin Opiorphin is an endogenous chemical compound first isolated from human saliva. Initial research with mice shows the compound has a painkilling effect greater than that of morphine. It works by stopping the normal breakup of enkephalins, natural ...

and spinorphin,

enkephalinase inhibitor An enkephalinase inhibitor is a type of enzyme inhibitor which inhibits one or more members of the enkephalinase class of enzymes that break down the endogenous enkephalin opioid peptides. Examples include racecadotril, ubenimex (bestatin), RB-1 ...

s (i.e., prevent the metabolism of enkephalins). *

Hemorphin Hemorphins are a class of naturally occurring, endogenous opioid peptides which are found in the bloodstream, and are derived from the β-chain of hemoglobin. They have antinociceptive effects via activation of the opioid receptors, and some may a ...

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 ...

-derived opioid peptides, including

hemorphin-4 Hemorphin-4 is an endogenous opioid peptide of the hemorphin family which possesses antinociceptive properties and is derived from the β-chain of hemoglobin in the bloodstream. It is a tetrapeptide with the amino acid sequence Tyr-Pro-Trp-Thr. ...

valorphin Valorphin, also known as VV-hemorphin-5, is a naturally occurring, endogenous opioid heptapeptide of the hemorphin family with the amino acid sequence H-Val-Val-Tyr-Pro-Trp-Thr-Gln-OH (VVYPWTQ). It is produced in the body via proteolyic cleavag ...

, and spinorphin, among others. While not peptides,

codeine Codeine is an opiate and prodrug of morphine mainly used to treat pain, coughing, and diarrhea. It is also commonly used as a recreational drug. It is found naturally in the sap of the opium poppy, ''Papaver somniferum''. It is typically use ...

and

morphine Morphine is a strong opiate that is found naturally in opium, a dark brown resin in poppies (''Papaver somniferum''). It is mainly used as a analgesic, pain medication, and is also commonly used recreational drug, recreationally, or to make ...

are also produced in the human body.

Exogenous

Exogenous opioid substances are called

exorphin Exorphins are exogenous opioid peptides, distinguished from endorphins, or endogenous opioid peptides. Exorphins include opioid food peptides like gluten exorphin and microbial opioid peptides and any other opioid peptide foreign to a host that h ...

s, as opposed to endorphines. Exorphins include

Gluten exorphin Gluten exorphins are a group of opioid peptides formed during the digestion of the gluten Gluten is a structural protein naturally found in certain cereal grains. Although "gluten" often only refers to wheat proteins, in medical literature it r ...

and

and are mostly contained in cereals and animal milk. They mimic the actions of endorphines because they bind to the same

s in the brain. These are the most common exorphins: *

Casomorphin Casomorphin is an opioid peptide (protein fragment) derived from the digestion of the milk protein casein. Health Digestive enzymes can break casein down into peptides that have some biological activity in cells and in laboratory animals though ...

(from

casein Casein ( , from Latin ''caseus'' "cheese") is a family of related phosphoproteins (CSN1S1, αS1, aS2, CSN2, β, K-casein, κ) that are commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of ...

found in milk of mammals, including cows) *

(from

gluten Gluten is a structural protein naturally found in certain cereal grains. Although "gluten" often only refers to wheat proteins, in medical literature it refers to the combination of prolamin and glutelin proteins naturally occurring in all grain ...

found in

cereal A cereal is any Poaceae, grass cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, Cereal germ, germ, and bran. Cereal Grain, grain crops are grown in greater quantit ...

s wheat, rye, barley) * Gliadorphin/gluteomorphin (from

found in cereals wheat, rye, barley) * Soymorphin-5 (from

soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu an ...

) *

Rubiscolin The rubiscolins are a group of opioid peptides that are formed during digestion of the ribulose bisphosphate carboxylase/oxygenase (Rubisco) protein from spinach leaves. These peptides have much in common with the better-known gluten exorphin Glu ...

(from

spinach Spinach (''Spinacia oleracea'') is a leafy green flowering plant native to central and western Asia. It is of the order Caryophyllales, family Amaranthaceae, subfamily Chenopodioideae. Its leaves are a common edible vegetable consumed either f ...

)

Amphibian

Deltorphin Deltorphin, also known as deltorphin A and dermenkephalin, is a natural product, naturally occurring, exogenous opioid peptide, opioid heptapeptide and thus, exorphin, with the amino acid sequence Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2. Along with the ...

Deltorphin I Deltorphin I, also known as -Ala2eltorphin I or deltorphin C, is a natural product, naturally occurring, exogenous opioid peptide, opioid heptapeptide and hence, exorphin, with the amino acid sequence Tyr-D-Ala-Phe-Asp-Val-Val-Gly-NH2. While n ...

Deltorphin II Deltorphin, also known as deltorphin A and dermenkephalin, is a naturally occurring, exogenous opioid heptapeptide and thus, exorphin, with the amino acid sequence Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2. Along with the other deltorphins (such as delt ...

Dermorphin Dermorphin is a hepta-peptide first isolated from the skin of South American frogs belonging to the genus ''Phyllomedusa''. The peptide is a natural opioid that binds as an agonist with high potency and selectivity to mu Opioid receptors. Dermorph ...

Synthetic

* Zyklophin – semisynthetic KOR antagonist derived from

dynorphin A Dynorphin A is a dynorphin, an endogenous opioid peptide with the amino acid sequence: Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-Pro-Lys-Leu-Lys. Dynorphin A1–8 is a truncated form of dynorphin A with the amino acid sequence: Tyr-Gly-Gly-Phe-Leu-Ar ...

References

External links

* {{InterPro content, IPR006024 Protein families