Random mutagenesis of G protein alpha subunit G(o)alpha. Mutations altering nucleotide binding

Area of Science:

• Molecular Biology
• Biochemistry
• Cell Signaling

Background:

• G protein alpha subunits are key regulators of cellular signaling.
• G(o)alpha is a specific alpha subunit involved in various cellular processes.
• Understanding nucleotide binding is crucial for G protein function.

Purpose of the Study:

• To identify mutations in G(o)alpha that affect its nucleotide binding properties.
• To characterize the functional consequences of these mutations.
• To explore the role of specific residues in guanine nucleotide interaction.

Main Methods:

• Random mutagenesis of G(o)alpha cDNA in Escherichia coli.
• In situ [35S]GTPγS binding assays on bacterial colonies.
• DNA sequencing and analysis of mutant clones.
• Functional expression in Xenopus laevis oocytes to assess G protein-coupled receptor signaling.

Main Results:

• Identified novel mutations reducing G(o)alpha affinity for GTPγS or Mg2+.
• Discovered mutations affecting residues previously unstudied in nucleotide binding.
• Demonstrated that some mutants retained beta gamma subunit interaction despite impaired GTPγS binding.
• Mutant S47C exhibited a dominant negative effect on thyrotropin-releasing hormone receptor signaling in oocytes.

Conclusions:

• Specific amino acid residues, including previously uncharacterized ones, are critical for G(o)alpha nucleotide binding.
• Disruption of nucleotide binding can lead to dominant negative phenotypes, impacting receptor-mediated signaling.
• This study provides insights into the structure-function relationship of G(o)alpha and its role in signal transduction.