You are working with a protein that you are trying to crysta

You are working with a protein that you are trying to crystallize. After initial attempts at determining conditions that allow your protein to remain properly folded and soluble, you discover that the best condition is with 500 mM NaCl. Upon sparse matrix screening, you discover that very small crystals are grown with a reservoir solution containing 100 mM Tris (pH 7.0), 10% polyethylene glycol 8000 and 100 mM NaCl. After optimizing your conditions, you discover that crystals grow bigger by steadily increasing the salt concentration of the reservoir (200-300 mM), but that crystals stop growing completely at 400 mM NaCl. Assume: that you set up each hanging drop with 2 mu L 2 mg/mL protein and 2 mu L reservoir solution, and polyethylene glycol does not contribute significantly to vapor diffusion. If vapor diffusion is exclusively due to [NaCl] and goes to completion, calculate the initial and final volumes of your hanging drop, and calculate the initial and final concentrations of your protein, polyethylene glycol, and NaCl. Do these calculations for reservoir solutions containing 100 mM, 200 mM, and 400 mM NaCl. Lastly, what is going on that causes your protein to crystallize?

Solution

Given, the experiment is set up each hanging drop with 2uL 2mg/ml protein and 2ul reservoir solution. It suggest that drop consist of 2uL solution in which the protein concentration is 2mg/mL.

Also the 2ml reservoir solution initially consist of 100mM Nacl, 100mM Tris and 10% PEG. Here the ratio is of 1:1:1 if we increase the conc of Nacl to 200mM then the protein concentration increased to 4ul and reservoir volume 4ul.

If we increase the volume of Nacl to 800mM then the protein concentration increased to 8ul and reservoir volume 8ul.The conc of PEG remain constant that is 10% of the total reservoir volume as the crystallization of protein is due to the increase in concentration of Nacl as protein precipitation is taking place in presence of salt which lead to the formation of protein crystals.

But it is given at final concentration of 400mM of Nacl protein crystals stop growing this is due to the fact that it reached its saturation point.