Structural basis for cyclic-nucleotide selectivity and cGMP-selective activation of PKG I

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Cyclic nucleotide-dependent protein kinases, PKG and PKA, are crucial for distinct signaling pathways.
• Understanding cyclic nucleotide selectivity is vital for segregating these pathways.
• The molecular mechanism underlying this selectivity remains largely unknown.

Purpose of the Study:

• To elucidate the molecular mechanism of cyclic nucleotide selectivity in PKG Iβ.
• To identify key residues responsible for cGMP binding specificity.
• To understand the structural basis of PKG activation.

Main Methods:

• X-ray crystallography to solve structures of the PKG Iβ C-terminal cyclic nucleotide binding domain (CNB-B) with and without cGMP.
• Comprehensive mutagenic analysis to identify key residues.
• Structural comparison of bound and unbound states.

Main Results:

• The PKG Iβ CNB-B domain exhibits high selectivity for cGMP.
• Leu296 and Arg297 were identified as critical residues for cGMP selectivity.
• cGMP binding induces large conformational changes in C-terminal helices, stabilized by Tyr351.
• These rearrangements provide insight into catalytic domain release and kinase activation.

Conclusions:

• Specific residues, Leu296 and Arg297, are key determinants of cGMP selectivity in PKG Iβ.
• Conformational changes upon cGMP binding are essential for kinase activation.
• This study provides a mechanical understanding of cyclic nucleotide selectivity and kinase activation.