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A common molecular weight of the androgen receptor monomer in different target tissues
Abstract:
Previously reported molecular weights for the monomeric steroid binding subunit of the androgen receptor protein have ranged from 25,000 to 167,000. The molecular weight appeared to vary among different species and target organs, as well as between different investigators. This study has examined androgen receptors from a diverse group of organs and species to determine whether these tissues share a common monomeric form. Gel filtration revealed peaks of specific [3H]dihydrotestosterone binding activity corresponding to Stokes radii of 54, 33, and 20 A in cytosols from several tissues. Phosphocellulose chromatography diminished the appearance of the smaller androgen receptor forms and facilitated the appearance of the larger 54-A form. Mixing experiments suggested that phosphocellulose was stabilizing the 54-A form by binding putative proteases which cleave this larger form. Methods were developed to generate homogenous preparations of a given androgen receptor size for comparative study. Sucrose density gradient analysis showed sedimentation coefficients of 4.5-5.0, 3.5-4.0, and 2.5-3.0 S, respectively. The corresponding calculated molecular weights were 109,000-121,000, 52,000-59,000, and 22,000-27,000. Scatchard analysis of each of these androgen receptor forms demonstrated very similar affinity for [3H]dihydrotestosterone (Kd approximately 1 nM), and each form possessed the ability to bind to DNA-cellulose. Extensively purified preparations of androgen receptor from R3327 tumor contained varying amounts of the three receptor forms even though molybdate and phosphocellulose were used to stabilize the androgen receptor protein during purification.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
This study investigated the androgen receptor (AR) protein, finding three distinct molecular forms across various tissues and species. These forms share similar binding affinities and DNA-binding capabilities, suggesting a common functional unit despite size variations.
Area of Science:
- Molecular Endocrinology
- Protein Biochemistry
- Steroid Receptor Research
Background:
- Reported molecular weights for the androgen receptor (AR) monomer vary widely (25,000–167,000 Da).
- Observed variations in AR molecular weight across species and tissues suggest potential differences in its monomeric form.
Purpose of the Study:
- To investigate if diverse tissues share a common monomeric form of the androgen receptor (AR).
- To characterize and compare different AR forms found in various biological samples.
Main Methods:
- Gel filtration chromatography to determine Stokes radii of AR binding activity.
- Phosphocellulose chromatography to analyze and stabilize AR forms.
- Sucrose density gradient centrifugation and Scatchard analysis to calculate molecular weights and binding affinities.
Main Results:
- Identified three distinct AR forms with Stokes radii of 54Å, 33Å, and 20Å.
- Calculated molecular weights for these forms ranged from 22,000–27,000 Da, 52,000–59,000 Da, and 109,000–121,000 Da.
- All identified AR forms exhibited similar high affinity for dihydrotestosterone (Kd ≈ 1 nM) and DNA-binding capacity.
Conclusions:
- The androgen receptor (AR) exists in at least three distinct molecular forms in various tissues.
- These AR forms are functionally similar in ligand binding and DNA interaction, despite size differences.
- Phosphocellulose chromatography can stabilize the larger AR form by inhibiting proteases responsible for generating smaller forms.