Atomic force microscopy imaging reveals the domain structure of polycystin-1

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Autosomal dominant polycystic kidney disease (ADPKD) is primarily caused by mutations in polycystin-1 (PC1).
• PC1 is a large protein (~460 kDa) with a complex multidomain structure, making biochemical and structural studies challenging.
• Previous knowledge of PC1's detailed structure and architecture was limited due to its size and handling difficulties.

Purpose of the Study:

• To determine the structural architecture of full-length polycystin-1 (PC1).
• To visualize individual PC1 molecules and their domains using advanced imaging techniques.
• To provide the first direct structural insights into PC1, aiding understanding of ADPKD.

Main Methods:

• Immunoaffinity chromatography was used to isolate wild-type and mutant PC1 from transfected cells.
• Atomic force microscopy (AFM) was employed for high-resolution imaging of individual PC1 molecules.
• Structural analysis of isolated PC1 variants to infer domain organization.

Main Results:

• Full-length PC1 visualized as two distinct blobs of unequal size connected by a 35 nm string.
• The smaller blob likely represents the N-terminus, and the larger blob the C-terminus, with the string comprising tandem polycystic kidney disease (PKD) domains.
• Structures of PC1 mutants were consistent with the proposed two-blob and string model, validating the architecture.

Conclusions:

• This study provides the first direct visualization of PC1 structure, revealing its unique architecture.
• The identified structure has significant implications for understanding PC1 function and the pathogenesis of ADPKD.
• The findings pave the way for future research into PC1's role in cellular processes and disease.