Signal Transduction Pathways
What role do G-proteins play in signal transduction?
G-proteins pass signals from receptors to enzymes, initiating reactions in the cell.
Why is specificity important in ligand binding?
Specificity ensures that only certain ligands can activate receptors, preventing unwanted signals.
How does the production of second messengers, such as cAMP, impact cellular signaling?
cAMP amplifies the signal, allowing a single activation to cause a large-scale response.
What are the key findings from amino acid modifications in glucagon?
Certain amino acids are essential for binding, while others drive the response; both charge and hydrophobic elements contribute.
What is the role of the histidine at position 1?
Removing His1 reduces both binding and biological activity, with a larger effect on activity than on binding. This suggests that His1 is important for both binding and signal transduction, with a greater role in signaling. The des-His1-des-Asp9 analog shows poor binding and no activity, emphasizing the importance of both residues. The des-His1-Lys9 analog binds well but lacks activity, showing that Asp9 is critical for signaling even if Lys can maintain binding. Adding negative Glu at positions 12, 17, or 18 prevents binding altogether.
How does glucagon binding lead to glucose release?
Glucagon binding activates a G-protein, which triggers reactions to release glucose.
Why were specific amino acids chosen for modification?
Positively charged amino acids help glucagon bind by interacting with negative charges in the receptor.
How do second messengers enhance signaling?
Second messengers like cAMP spread and strengthen signals, expanding the cell’s response.
Why modify glucagon’s amino acids to develop an antagonist?
Modifying amino acids can prevent glucagon from activating the receptor fully, which could help manage high glucose levels.
What is the effect of substituting or eliminating the amino acid at position 9?
decreases receptor binding and biological activity, suggesting that Asp is essential for both. Substituting Asp with Lys cuts binding by half and eliminates biological activity. This implies that Asp's structure, rather than its charge, is key for binding and activity.
How does signal termination ensure regulation?
Termination prevents overstimulation, keeping cellular responses balanced and controlled.
What is the effect of modifying specific amino acids?
Altering amino acids impacts binding and activity, showing the role of each in glucagon’s function.
How old is bunsen
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What are the potential therapeutic applications of glucagon antagonists?
Glucagon antagonists may help control diabetes by reducing glucose release from the liver, especially in combination with insulin.
What is the effect of the amino acid replacement or modification at position 12?
Eliminating the positive charge at position 12 reduces binding by 50–90%, although bound analogs can still elicit a biological response. Nonpolar analogs (such as Ala and acetylated Lys) bind better than Gly12, implying nonpolar interactions are vital for binding. Adding a negative charge at position 12 nearly abolishes binding, suggesting that the positive charge may interact with a negative charge on the receptor.
Of the glucagon analogs presented here, which is the best glucagon antagonist? Could you design a better glucagon antagonist than the analogs presented here? Explain the rationale for your design.
The des-His1-Lys9 is the best antagonist because it binds to receptors with 70% of the native hormone's affinity but has no biological activity. In this version, the key amino acids for signaling have been modified, while the essential positively charged residues for binding (positions 12, 17, and 18) are preserved. A stronger antagonist might be created by carefully selecting different replacements at position 9 to maintain binding properties but prevent signaling
What is the effect of the amino acid replacement at position 17? Be specific.
Leu17 binds less effectively than Ala17 but demonstrates greater activity once bound, which supports the role of hydrophobic interactions between the hormone and receptor since Leu has a more hydrophobic side chain than Ala. Substitution with Glu reduces binding, although less drastically than at position 12.
What is the effect of the amino acid replacement at position 18? Be specific.
The findings confirm that hydrophobic interactions are crucial, as alanine replacement decreases binding more than leucine. The positive charge is also significant, as replacing it with negatively charged glutamate reduces binding by over 90%.