by Peter Nollert
September 11, 2009 06:00
Need a simple way to test the effect of multiple temperatures on your protein crystallization trials? Take a thermometer and explore temperatures in your lab environment! There's plenty of evidence in the literature that temperature plays a role in successful protein crystallization. In some cases temperature is the crucial parameter to get right for growing well-diffracting crystals.
The BMCDB gives a good impression regarding temperatures that have worked well for protein crystallization in the past:
Protein crystallization temperatures taken from BMCD 4.02. Note that the most favorite temperatures are those found in the lab and in a fridge.
I do think that the peaks at 4C and 20C are due to investigator bias and there's no scientific reasoning that these temperatures provide you with the highest crystallization success or best crystal quality. Since room temp. is so convenient, many labs underutilize this parameter as their primary way to optimize protein crystal growth.
Of course there are high-end incubators, but these are expensive and as a result, resourceful researchers have found cheap ways to access temperatures that are different from that on the lab bench.
If you want to explore more crystal growth temperatures for your protein crystallization experiments - get yourself a thermometer and go on a temperature hunt around you. How many different temperatures can you localize?
• Laboratory room temperature - that's easy, but there's potential to discover more than your standard 22C. You're in good shape if you've got an air conditioning system running, this provides you with a constant temperature. But even in air conditioned rooms you will often find spots that are warmer (i.e. on the top shelf, behind the fridge, on top of a warm instrument/monitor) or colder (next to the AC vent) and that are different form the temperature on the lab bench. Can you find stable microclimates at 20, 22, 24, 26 and 28C?
• Office space sometimes has a different temperature from your lab. (Please use common sense and talk to your safety officer when placing crystallization experiments outside of the lab; i.e. no heavy metal solutions)
• Lab reagent storage fridge or cold room: 4°C. Testing different spots in the fridge may give you a 2C and a 6C spot.
• E.coli incubator or incubation room : 37C, often there's also a 27C or 40C incubator that is used to induce protein expression.
Tip: Measure temperatures several times to identify and avoid spots with undesired temperature fluctuations. Once you've decided on a particular spot: make sure that the crystallization tray is placed inside a container that dampens temperature changes, such as a styrofoam box with an equilibrated cooling element to provide for some extra heat capacity.
All the best,
Peter