The stability and aggregation properties of the GTPase domain from human SEPT4.

Abstract

The septins are a family of conserved proteins involved in cytokinesis and cortical organization. An increasing amount of data implicates different septins in diverse pathological conditions including neurodegenerative disorders, neoplasia and infections. Human SEPT4 is a member of this family and its tissue-specific ectopic expression profile in colorectal and urologic cancer makes it a useful diagnostic biomarker. Thermal unfolding of the GTPase domain of SEPT4 (SEPT4-G) revealed an unfolding intermediate which rapidly aggregates into amyloid-like fibers under physiological conditions. In this study, we examined the effects of protein concentration, pH and metals ions on the aggregation process of recombinant SEPT4-G using a series of biophysical techniques, which were also employed to study chemical unfolding and stability. Divalent metal ions caused significant acceleration to the rate of SEPT4-G aggregation. Urea induced unfolding was shown to proceed via the formation of a partially unfolded intermediate state which unfolds further at higher urea concentrations. The intermediate is a compact dimer which is unable to bind GTP. At 1 M urea concentration, the intermediate state was plagued by irreversible aggregation at temperatures above 30 degrees C. However, higher urea concentration resulted in a marked decay of the aggregation, indicating that the partially folded structures may be necessary for the formation of these aggregates. The results presented here are consistent with the recently determined crystal structure of human septins and shed light on the aggregation properties of SEPT4 pertinent to its involvement in neurodegenerative disease.

• Authors: Wanius Garcia, Nathalia C Rodrigues, Mario de Oliveira Neto, Ana Paula Ulian de Araújo, Igor Polikarpov, Manami Tanaka, Tomoo Tanaka, Richard C Garratt
• Journal: Biochimica et biophysica acta (Biochim Biophys Acta) Vol. 1784 Issue 11 Pg. 1720-7 (Nov 2008) ISSN: 0006-3002 [Print] Netherlands
• PMID: 18617022 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Amyloid
• Cytoskeletal Proteins
• Polymers
• GTP Phosphohydrolases
• SEPTIN4 protein, human
• Septins

Topics

• Amyloid (metabolism)
• Circular Dichroism
• Cytoskeletal Proteins (chemistry, metabolism)
• GTP Phosphohydrolases (chemistry, metabolism)
• Humans
• Models, Biological
• Polymers (chemistry, metabolism)
• Protein Binding
• Protein Denaturation
• Protein Folding
• Protein Structure, Tertiary
• Scattering, Small Angle
• Septins
• X-Ray Diffraction