Hello,
Recently I asked my colleague whether we may simply microwave culture media for mammalian cell culture in order to warm it prior to use. He told me that we may not microwave cell culture media because it will destroy the conformation of native proteins in the fetal bovine serum (FBS) component. So apparently, the higher structure of proteins (quaternary, tertiary) is important in how the media sustains the cells. Why is this? Do the proteins present in the FBS actually interact with the cells in a receptor-mediated fashion as human proteins would in the body? If so, would this not introduce unwanted artifacts due to the differences between human and bovine proteins?
Along this line of reasoning: why is microwaving food for human consumption seen as alright? Is the type of metabolism occurring upon human consumption very different from that in cells upon media change? I understand that food consumed by mastication is ultimately taken to the stomach, where food proteins are cleaved by the protease pepsin. But before food enters the stomach, many cells must see the food proteins in their native form, that is, if the food was consumed raw. Does microwaving introduce changes in food proteins? Are these changes undesirable in the context of health and disease? Why is it so important to maintain the conformation of serum proteins in mammalian cell culture media?
Thank you!
Microwaving is absolutely brutal vs proteins, compared with just warming it in a waterbath. I don't know how that works, but something about the microwaves just knocks them out of solution even before the liquid as a whole warms up at all. Try it and see!
So that's the main thing -- they don't just misfold, but as they misfold the hydrophobic interior shows up on the outside, interacts with other misfolded proteins, and they fall out of solution. You could plausibly have important serum proteins that still technically "work" even when misfolded. For example in the 459 amino acid vitronectin adhesion molecule, the "business end" that really "glues the cells to the glass" is just the integrin binding motif "RGD". A tripeptide with no structure to speak of. The tripeptide alone works just fine in promoting cell adhesion. But denatured vitronectin doesn't, because it's all clumped up and can't diffuse out to the cells and find their receptors anymore.
Of course you can have issues of bovine proteins not reacting with human receptors. This does not matter enough to prevent cell culture from working well enough for most people. If you want to make some old boys in the field very unhappy, you could start asking such questions experimentally. You can buy adult human donor serum for cell culture. Those are supposed to miss out on some of the "fetal" super growth factors the FBS is widely believed to have. As far as I'm aware nobody has attempted to venture into the fetal human serum business. That's probably for the better.
And while you're taking on entrenched academic beliefs, sure, why not also the food industry! We humans usually denature the proteins in our food by cooking or various sterilization procedures. That's of course done to kill pathogens, but it's going to hit most of the harmless food proteins as a result. For example, did you know milk comes out of the cow almost clear? It's white in the grocery store only because people "pasteurized" it, denaturing all its proteins, and making them fall out of solution. So to argue that microwaving is "bad", you'd need to find something special about it that goes beyond the regular heat denaturation we already have in most our food. Can you think of a testable hypothesis? There are many enemies to be made out there.
I love your questions (in case you can't tell :). Keep asking the tough ones!
The use of fetal bovine serum in cell culture is to provide growth factors that support the cells' ability to grow and divide. These proteins must be in their native conformation in order to interact with receptors on the surface of the cells and have their effect.
The problem with using a microwave oven to warm the medium before use is that it does not heat the solution evenly, resulting in hot spots at which protein denaturation can occur. The medium also contains a lot of bovine serum albumin, which could coagulate if overheated.
People don't normally consume uncooked fetal bovine serum, so we are not exposed, even briefly, to the growth factors in it. Even if people did do that, the exposure would be so brief before the proteins were destroyed in the digestive tract, that it is unlikely that they would have any effect.
For human cells in culture, it is likely that human growth factors would be more effective than bovine ones, but fetal bovine serum is readily available. If desired, cell cultures can be transitioned from fetal bovine serum to serum-free medium, which contains purified growth factors. I'm not sure whether such media can be obtained with specifically human growth factors.
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