Androgen receptor binding conversion
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Androgen Receptor Binding Conversion: Mechanisms and Structural Insights
Post-Translational Modification and Phosphorylation in Androgen Receptor Binding
The androgen receptor (AR) undergoes post-translational modifications that affect its molecular weight and function. In LNCaP cells, the AR is initially synthesized as a 110 kDa protein and is rapidly converted to a 112 kDa form through phosphorylation. Both forms are capable of binding hormones and transforming into a nuclear binding form, indicating that phosphorylation is not required for hormone binding or receptor transformation, but it does reflect a conversion process in the receptor's lifecycle .
Ligand-Binding Domain (LBD) Dimerization and Its Role in AR Function
Dimerization of the AR ligand-binding domain is essential for its proper function. Agonist binding induces dimerization of the AR-LBD, which is necessary for transcriptional activation and the development of AR-dependent tissues. Disruption of this dimerization impairs DNA binding, ligand binding, and co-regulator interactions, leading to loss of AR-regulated gene expression and physiological effects, even when hormone binding and nuclear translocation are intact 26. The dimerization interface is also a target for novel AR antagonists, which can inhibit AR activity by disrupting the hydrogen-bonding network between monomers, offering a new mechanism for AR inhibition .
Structural Dynamics: Agonist vs. Antagonist Binding
The AR exhibits different structural dynamics depending on whether it is bound to an agonist or antagonist. Agonist binding increases the mobility of residues at allosteric and co-activator binding sites, facilitating transcriptional activity. In contrast, antagonist binding decreases this mobility, stabilizing the receptor in an inactive conformation. Key residues such as Thr877 and Asn705 are involved in hydrogen bonding with agonists, a feature absent in antagonist binding 35. Molecular dynamics simulations reveal that ligand binding can reposition helix 12 (H12) of the AR-LBD, which is crucial for the transition between active and inactive forms of the receptor .
Conversion of Antagonist to Agonist Activity and Resistance Mechanisms
Increased AR expression can lead to resistance to antiandrogen therapy. When AR levels are elevated, antagonists can paradoxically act as agonists, promoting cancer cell growth. This conversion is linked to changes in coactivator and corepressor recruitment at AR target genes and depends on a functional ligand-binding domain. Thus, the AR's ability to switch between antagonist and agonist responses is a key factor in therapy resistance .
Binding Properties and Specificity of Androgen Receptors
Androgen receptors in different tissues (testis, epididymis, prostate) have similar binding affinities for testosterone and dihydrotestosterone, with a slightly higher affinity for dihydrotestosterone. The binding process is influenced by temperature, pH, and the presence of specific androgens, but the receptor's specificity is consistent across tissues. The stability of the receptor is enhanced when bound to androgen, and competitive binding assays confirm the receptor's selectivity for its natural ligands .
Residue-Specific Contributions to Ligand Binding
Quantitative analysis of AR-ligand interactions shows that hydrophobic residues in the ligand-binding pocket are critical for binding, primarily through van der Waals interactions. These hotspot residues contribute significantly to the overall binding free energy, and understanding their roles can inform the design of more effective AR inhibitors .
Conclusion
Androgen receptor binding conversion involves a complex interplay of post-translational modifications, dimerization, ligand-induced structural changes, and tissue-specific binding properties. Phosphorylation and dimerization are key steps in AR activation, while ligand binding dynamics and residue-specific interactions determine the receptor's response to agonists and antagonists. These mechanisms are central to understanding AR function, resistance to therapy, and the development of new AR-targeted drugs 1234+5 MORE.
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