Structural and functional analysis of Saccharomyces cerevisiae Mob1

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Mob proteins act as crucial activator subunits for the Dbf2/Dbf20 family of protein kinases.
• Previous structural studies of Mob1 proteins focused on the conserved C-terminal core, omitting the variable N-terminal region.

Purpose of the Study:

• To elucidate the complete structure of Saccharomyces cerevisiae Mob1, including its variable N-terminal region.
• To identify and characterize novel structural elements within the Mob1 N-terminus.
• To investigate the functional significance of these N-terminal elements in Mob1's interaction with Dbf2/Dbf20 kinases.

Main Methods:

• X-ray crystallography to determine the 2.0 Å structure of Saccharomyces cerevisiae Mob1.
• Identification of novel structural elements: alpha-helix H0, strand-like element S0, and beta strand S-1.
• In vivo functional analysis using Mob1 mutants targeting the identified N-terminal elements.

Main Results:

• The crystal structure reveals three novel N-terminal elements: helix H0, strand S0, and strand S-1.
• Helix H0 mediates intermolecular association, forming Mob1 homodimers.
• Strand S0 binds intramolecularly to the core domain, potentially occluding the Dbf2 binding site.

Conclusions:

• The N-terminal region of Mob1 contains functionally critical structural elements, including those involved in homodimerization and regulation of kinase interaction.
• Targeting helix H0 or its binding site in vivo compromises Mob1's biological function.
• The complete Mob1 structure provides insights into the regulation of Dbf2/Dbf20 protein kinases.