Queue Gaps Among the IQGAPs in Dictyostelium discoideum

Area of Science:

• Cell Biology
• Molecular Biology
• Evolutionary Biology

Background:

• IQGAP proteins are crucial scaffold proteins regulating actin cytoskeleton dynamics.
• While animal IQGAPs are well-studied, their evolutionary conservation in other eukaryotes like protists is less understood.
• Dictyostelium discoideum offers a model system to investigate conserved IQGAP functions.

Purpose of the Study:

• To characterize IQGAP-related proteins in Dictyostelium discoideum.
• To investigate the structural and functional conservation of Dictyostelium IQGAPs with their animal counterparts.
• To elucidate the specific roles of different Dictyostelium IQGAP family members in cellular processes.

Main Methods:

• Domain organization analysis of Dictyostelium IQGAP proteins.
• 3D structure prediction using AlphaFold 3.
• Cellular localization studies.
• Interaction studies with F-actin and GTPases (Rac1, small GTPases).
• Functional assays for cell adhesion, growth, cytokinesis, and macroendocytosis.

Main Results:

• Four Dictyostelium proteins were identified as IQGAP family members, exhibiting conserved functions in actin cytoskeleton regulation despite structural differences.
• Predicted 3D structures of Dictyostelium IQGAPs resemble the C-terminal half of human IQGAP1, supporting common ancestry.
• IqgD localizes to the cell cortex, interacts with F-actin and Rac1, and promotes cell adhesion and growth.
• DGAP1 and GAPA play opposing roles in regulating contractile cortical assemblies essential for cytokinesis and morphogenesis.
• IqgC, related to fungal GAP1 proteins, possesses RasGAP activity and regulates macroendocytosis and cell adhesion.

Conclusions:

• Dictyostelium IQGAP proteins are functionally conserved with animal IQGAPs, playing vital roles in cell motility, endocytosis, cytokinesis, and adhesion.
• Structural predictions support a common evolutionary origin for IQGAP proteins across distant species.
• Distinct Dictyostelium IQGAP members (IqgD, DGAP1, GAPA, IqgC) have specialized functions, highlighting the versatility of this protein family in regulating fundamental cellular processes.