Use of Dynamic Light Scattering to Detect the

Use of Dynamic Light Scattering to Detect the Growth of Amyloid Fibrils in HEWL.

What are they? Why should we study them? • Proteins bonded in a very specific manner • How they are formed is not understood • Associated with many diseases, including: – Alzheimer’s Disease – Mad Cow Disease

Hen Egg White Lysozyme • In water, HEWL is in folded state – Hydrogen bonding • TFE partially unfolds, then stabilizes HEWL • Newly exposed portions of HEWL should bond to each other, forming strands

How Could We Study Them? • We wanted to characterize their rate of formation • Disturbing the proteins would make any data collected questionable • How could we solve this problem?

Dynamic Light Scattering!

What is DLS? • Detects the changing interference pattern of laser light scattered by small particles in solution. • From the rate of change, we can measure the diffusion rate and size of the particles.

Light Scattering in Action!

What is the Autocorrelation Function? • Put simply: the average of the time varying portion of the intensity at some initial time, t, with the time varying portion of the intensity at some later time, t+∆t.

OK, It isn’t really that simple… • This calculation is done for many values of ∆t. • It is repeated many times (in our case, ~400), each time averaging the new result with the average of all the previous results.

Why would you do that? • For small values of ∆t, the signal is still correlated with the signal at t = 0; positive average intensity. • For large values of ∆t, this is not true, and the autocorrelation function will eventually average out to zero.

Key Point • By measuring how long it takes the function to go to zero, we can tell how fast the particles are moving!

For All You Visual Learners…

Microsphere Autocorrelation Function, τ = 3. 89 ms.

Single Exponential Autocorrelation Function

Multiple Exponential Autocorrelation Function

Multiple exponential fit

Evolution of the Autocorrelation Function

Time Constants Vs. Incubation Time

In Conclusion • Succeeded in producing a DLS setup • Induced aggregation in HEWL with TFE • Unable to prove that aggregate contained Amyloid Fibrils • With more time, experiment could be completed

Special Thanks Dr. Stephen Hagen Dr. Robert De. Serio Caleb Carswell University of Florida Physics Department

(Applause)