Got a crystal hit? 💎
Now the real work begins – optimizing that condition to grow larger, well-diffracting crystals. Start by varying one factor at a time around the hit: perform grid screens of precipitant, salt, buffer and protein concentrations as well as pH in a finer range around the initial hit point.
For example, if a crystal appeared in 20% PEG 3350, 0.1 M HEPES pH 7.5, try 15–25% PEG3350 and pH 7.0–8.0 in small increments. Small tweaks can have big effects – even 0.1 pH units or a few percent precipitant can turn crystals on or off. Also consider additive screens (small molecules or ions that might stabilize the crystal lattice) and try different drop ratios or seeding (if crystals are small, rare or have non-optimal morphology). Document every tweak – optimization is an iterative, data-driven process. If you have different morphologies, then always remember that you can’t judge a book by it’s cover. Sometimes the ugliest crystals might exhibit the best diffraction. Therefore it is important to not just optimize “by eye” but also check diffraction quality during the optimization.
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