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Nanomechanical properties of α-synuclein amyloid fibrils: a comparative study by nanoindentation, harmonic force microscopy, and Peakforce QNM.

Sweers K, van der Werf K, Bennink M, Subramaniam V - Nanoscale Res Lett (2011)

Bottom Line: For nanomechanical measurements, we used single-point nanoindentation, in which the AFM tip as the indenter is moved vertically to the fibril surface and back while the force is being recorded.We also used two recently developed AFM surface property mapping techniques: Harmonic force microscopy (HarmoniX) and Peakforce QNM.We discuss the relative merits of these three methods for the determination of the elastic properties of protein fibrils, particularly considering the differences and difficulties of each method.

View Article: PubMed Central - HTML - PubMed

Affiliation: Nanobiophysics Group, MESA+ Institute for Nanotechnology, Faculty of Science and Technology, University of Twente, Enschede, The Netherlands. k.k.m.sweers@utwente.nl.

ABSTRACT
We report on the use of three different atomic force spectroscopy modalities to determine the nanomechanical properties of amyloid fibrils of the human α-synuclein protein. α-Synuclein forms fibrillar nanostructures of approximately 10 nm diameter and lengths ranging from 100 nm to several microns, which have been associated with Parkinson's disease. Atomic force microscopy (AFM) has been used to image the morphology of these protein fibrils deposited on a flat surface. For nanomechanical measurements, we used single-point nanoindentation, in which the AFM tip as the indenter is moved vertically to the fibril surface and back while the force is being recorded. We also used two recently developed AFM surface property mapping techniques: Harmonic force microscopy (HarmoniX) and Peakforce QNM. These modalities allow extraction of mechanical parameters of the surface with a lateral resolution and speed comparable to tapping-mode AFM imaging. Based on this phenomenological study, the elastic moduli of the α-synuclein fibrils determined using these three different modalities are within the range 1.3-2.1 GPa. We discuss the relative merits of these three methods for the determination of the elastic properties of protein fibrils, particularly considering the differences and difficulties of each method.

No MeSH data available.


Related in: MedlinePlus

Effective spring constant as a function of sample stiffness. (A) Force versus z piezo displacement curve in case of sample spring constant larger, the same or lower compared to the spring constant of the cantilever. (B) Effective spring constant (keff, representing the slope of the force curves in A) as a function of the stiffness of the sample. From the slope of this curve it is clear that the maximum sensitivity is achieved when both spring constants are of the same order of magnitude.
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Figure 6: Effective spring constant as a function of sample stiffness. (A) Force versus z piezo displacement curve in case of sample spring constant larger, the same or lower compared to the spring constant of the cantilever. (B) Effective spring constant (keff, representing the slope of the force curves in A) as a function of the stiffness of the sample. From the slope of this curve it is clear that the maximum sensitivity is achieved when both spring constants are of the same order of magnitude.

Mentions: In order to measure the elastic properties of a material, the choice of the cantilever is key. In nanoindentation the highest sensitivity (and thus accuracy) is achieved if the spring constant of the probe cantilever is identical to the effective spring constant of the sample (also referred to as contact stiffness), see Figure 6. If the spring constant of the cantilever is more than 10 times lower or higher than that of the sample, the sensitivity is about 3 times lower, see Figure 6 making the determination of the elastic modulus less accurate. Practically since one does not know the stiffness of the sample a priori, an estimation is necessary. This is also the case for the surface mapping methods. The nominal elastic modulus ranges accessible by HarmoniX and Peakforce QNM are 10 MPa-10 GPa and 0.7 MPa-70 GPa, respectively [18]. However, as noted above, this range depends on the cantilever that is used for the measurements and is in practice significantly smaller.


Nanomechanical properties of α-synuclein amyloid fibrils: a comparative study by nanoindentation, harmonic force microscopy, and Peakforce QNM.

Sweers K, van der Werf K, Bennink M, Subramaniam V - Nanoscale Res Lett (2011)

Effective spring constant as a function of sample stiffness. (A) Force versus z piezo displacement curve in case of sample spring constant larger, the same or lower compared to the spring constant of the cantilever. (B) Effective spring constant (keff, representing the slope of the force curves in A) as a function of the stiffness of the sample. From the slope of this curve it is clear that the maximum sensitivity is achieved when both spring constants are of the same order of magnitude.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211334&req=5

Figure 6: Effective spring constant as a function of sample stiffness. (A) Force versus z piezo displacement curve in case of sample spring constant larger, the same or lower compared to the spring constant of the cantilever. (B) Effective spring constant (keff, representing the slope of the force curves in A) as a function of the stiffness of the sample. From the slope of this curve it is clear that the maximum sensitivity is achieved when both spring constants are of the same order of magnitude.
Mentions: In order to measure the elastic properties of a material, the choice of the cantilever is key. In nanoindentation the highest sensitivity (and thus accuracy) is achieved if the spring constant of the probe cantilever is identical to the effective spring constant of the sample (also referred to as contact stiffness), see Figure 6. If the spring constant of the cantilever is more than 10 times lower or higher than that of the sample, the sensitivity is about 3 times lower, see Figure 6 making the determination of the elastic modulus less accurate. Practically since one does not know the stiffness of the sample a priori, an estimation is necessary. This is also the case for the surface mapping methods. The nominal elastic modulus ranges accessible by HarmoniX and Peakforce QNM are 10 MPa-10 GPa and 0.7 MPa-70 GPa, respectively [18]. However, as noted above, this range depends on the cantilever that is used for the measurements and is in practice significantly smaller.

Bottom Line: For nanomechanical measurements, we used single-point nanoindentation, in which the AFM tip as the indenter is moved vertically to the fibril surface and back while the force is being recorded.We also used two recently developed AFM surface property mapping techniques: Harmonic force microscopy (HarmoniX) and Peakforce QNM.We discuss the relative merits of these three methods for the determination of the elastic properties of protein fibrils, particularly considering the differences and difficulties of each method.

View Article: PubMed Central - HTML - PubMed

Affiliation: Nanobiophysics Group, MESA+ Institute for Nanotechnology, Faculty of Science and Technology, University of Twente, Enschede, The Netherlands. k.k.m.sweers@utwente.nl.

ABSTRACT
We report on the use of three different atomic force spectroscopy modalities to determine the nanomechanical properties of amyloid fibrils of the human α-synuclein protein. α-Synuclein forms fibrillar nanostructures of approximately 10 nm diameter and lengths ranging from 100 nm to several microns, which have been associated with Parkinson's disease. Atomic force microscopy (AFM) has been used to image the morphology of these protein fibrils deposited on a flat surface. For nanomechanical measurements, we used single-point nanoindentation, in which the AFM tip as the indenter is moved vertically to the fibril surface and back while the force is being recorded. We also used two recently developed AFM surface property mapping techniques: Harmonic force microscopy (HarmoniX) and Peakforce QNM. These modalities allow extraction of mechanical parameters of the surface with a lateral resolution and speed comparable to tapping-mode AFM imaging. Based on this phenomenological study, the elastic moduli of the α-synuclein fibrils determined using these three different modalities are within the range 1.3-2.1 GPa. We discuss the relative merits of these three methods for the determination of the elastic properties of protein fibrils, particularly considering the differences and difficulties of each method.

No MeSH data available.


Related in: MedlinePlus