Heteromer

A heteromer is something that consists of different parts. Examples are:

Biology

• Spinal neurons that pass over to the opposite side of the spinal cord.^[1]
• A protein complex that contains two or more different polypeptides.^[2]

Pharmacology

• Ligand-gated ion channels such as the nicotinic acetylcholine receptor and GABA_A receptor are composed of five subunits arranged around a central pore that opens to allow ions to pass through. There are many different subunits available that can come together in a wide variety of combinations to form different subtypes of the ion channel.^[3][4][5] Sometimes the channel can be made from only one type of subunit, such as the α7 nicotinic receptor, which is made up from five α7 subunits, and so is a homomer rather than a heteromer, but more commonly several different types of subunit will come together to form a heteromeric complex (e.g., the α4β2 nicotinic receptor, which is made up from two α4 subunits and three β2 subunits). Because the different ion channel subtypes are expressed to different extents in different tissues, this allows selective modulation of ion transport and means that a single neurotransmitter can produce varying effects depending on where in the body it is released.^[6][7][8]
• G protein-coupled receptors are composed of seven membrane-spanning alpha-helical segments that are usually linked together into a single folded chain to form the receptor complex. However, research has demonstrated that a number of GPCRs are also capable of forming heteromers from a combination of two or more individual GPCR subunits under some circumstances, especially where several different GPCRs are densely expressed in the same neuron. Such heteromers may be between receptors from the same family (e.g., adenosine A₁/A_2A heteromers^[9][10] and dopamine D₁/D₂^[11] and D₁/D₃ heteromers^[12]) or between entirely unrelated receptors such as CB₁/A_2A,^[13] glutamate mGluR₅ / adenosine A_2A heteromers,^[14] cannabinoid CB₁ / dopamine D₂ heteromers,^[15] and even CB₁/A_2A/D₂ heterotrimers where three different receptors have come together to form a heteromer.^[16][17] The ligand binding properties and intracellular trafficking pathways of GPCR heteromers usually show elements from both parent receptors, but may also produce quite unexpected pharmacological effects, making such heteromers an important focus of current research.^{[18][19][20][21][22]}

See also

• GPCR oligomer

References

1. Medical dictionary
2. Merriam-Webster Dictionary
3. Gotti C, Moretti M, Gaimarri A, Zanardi A, Clementi F, Zoli M (October 2007). "Heterogeneity and complexity of native brain nicotinic receptors". Biochemical Pharmacology 74 (8): 1102–11. doi:10.1016/j.bcp.2007.05.023. PMID 17597586.
4. Millar NS, Gotti C (January 2009). "Diversity of vertebrate nicotinic acetylcholine receptors". Neuropharmacology 56 (1): 237–46. doi:10.1016/j.neuropharm.2008.07.041. PMID 18723036.
5. Collins AC, Salminen O, Marks MJ, Whiteaker P, Grady SR (2009). "The road to discovery of neuronal nicotinic cholinergic receptor subtypes". Handbook of Experimental Pharmacology. Handbook of Experimental Pharmacology 192 (192): 85–112. doi:10.1007/978-3-540-69248-5_4. ISBN 978-3-540-69246-1. PMID 19184647.
6. Graham AJ, Martin-Ruiz CM, Teaktong T, Ray MA, Court JA (August 2002). "Human brain nicotinic receptors, their distribution and participation in neuropsychiatric disorders". Current Drug Targets. CNS and Neurological Disorders 1 (4): 387–97. doi:10.2174/1568007023339283. PMID 12769611.
7. Nutt D (April 2006). "GABAA receptors: subtypes, regional distribution, and function". Journal of Clinical Sleep Medicine 2 (2): S7–11. PMID 17557501.
8. Heldt SA, Ressler KJ (December 2007). "Forebrain and midbrain distribution of major benzodiazepine–sensitive GABAA receptor subunits in the adult C57 mouse as assessed with in situ hybridization". Neuroscience 150 (2): 370–85. doi:10.1016/j.neuroscience.2007.09.008. PMC 2292345. PMID 17950542.
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14. Zezula J, Freissmuth M (March 2008). "The A2A-adenosine receptor: a GPCR with unique features?". British Journal of Pharmacology. 153 Suppl 1 (S1): S184–90. doi:10.1038/sj.bjp.0707674. PMC 2268059. PMID 18246094.
15. Marcellino D, Carriba P, Filip M, Borgkvist A, Frankowska M, Bellido I, Tanganelli S, Müller CE, Fisone G, Lluis C, Agnati LF, Franco R, Fuxe K (April 2008). "Antagonistic cannabinoid CB1/dopamine D2 receptor interactions in striatal CB1/D2 heteromers. A combined neurochemical and behavioral analysis". Neuropharmacology 54 (5): 815–23. doi:10.1016/j.neuropharm.2007.12.011. PMID 18262573.
16. Carriba P, Navarro G, Ciruela F, Ferré S, Casadó V, Agnati L, Cortés A, Mallol J, Fuxe K, Canela EI, Lluis C, Franco R (2008). "Detection of heteromerization of more than two proteins by sequential BRET-FRET". Nature Methods 5 (8): 727–33. doi:10.1038/nmeth.1229. PMID 18587404.
17. Ferré S, Goldberg SR, Lluis C, Franco R (2009). "Looking for the role of cannabinoid receptor heteromers in striatal function". Neuropharmacology. 56 Suppl 1 (Suppl 1): 226–34. doi:10.1016/j.neuropharm.2008.06.076. PMC 2635338. PMID 18691604.
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