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Identification of structurally distinct alpha 2-adrenergic receptors
S M Lanier1, C J Homcy, C Patenaude
1Cardiac Unit, Massachusetts General Hospital, Boston.
The Journal of Biological Chemistry
|October 5, 1988
Summary
Alpha 2-adrenergic receptors show diversity, with distinct isoforms found in human platelets and neonatal rat lungs. These structural differences explain variations in how these receptors bind to ligands.
Area of Science:
- Pharmacology
- Molecular Biology
- Neuroscience
Background:
- Membrane receptors and ion channels exhibit diversity through tissue-specific and developmentally regulated isoforms.
- Alpha 2-adrenergic receptors are key in sympathetic neurotransmission and display varied effector cell responses via multiple signal transduction pathways.
- Differences in ligand recognition properties among alpha 2-adrenergic receptors across tissues and species suggest potential heterogeneity.
Purpose of the Study:
- To investigate if structural heterogeneity of the alpha 2-adrenergic receptor protein contributes to observed diversity in ligand recognition.
- To structurally characterize alpha 2-adrenergic receptors from human platelets and neonatal rat lung, tissues with significant differences in ligand binding.
Main Methods:
- Partial purification (50-100-fold) of alpha 2-adrenergic receptors from human platelet and neonatal rat lung tissues.
- Characterization of physical and structural properties, including apparent molecular weight of hormone-binding subunits and oligosaccharide moieties.
Main Results:
- Differences in ligand recognition were maintained after partial receptor purification.
- Significant distinctions were observed in the physical and structural properties of the alpha 2-adrenergic receptors.
- The human platelet receptor subunit had an apparent molecular weight of approximately 64,000 Da, while the neonatal rat lung receptor subunit was approximately 44,000 Da.
- Variations in the number or type of associated oligosaccharide moieties were identified between the two receptor types.
Conclusions:
- The observed structural diversity in alpha 2-adrenergic receptors supports the hypothesis of isoform expression.
- These findings suggest that multiple genes encode distinct, yet similar, alpha 2-adrenergic receptor proteins.
- The structural heterogeneity identified is directly linked to the functional differences in ligand recognition properties.