I'm planning to add functionalities to a protein molecule using certain amino acids in its backbone. I would just like to ask, why is it stated that "it is essential that amino acid building blocks are obtained in high enantiomeric purity"? How is this fact important? I'm just seeking to add functionalities on proteins to be used for click chemistry and I'm looking for possible ways to do this on serine residues.
As proteins are chiral molecules able to recognise chiral ligands in a stereo/enantiospecific manner, it is essential to have enantiopure amino acids (serine in your case) to assure a good folding, recognition and reactivity. I highly recommend to pay more for a good purity (>99%) to assure correct addition of functionalities on your protein.
I guess because changing the configuration of just one residue can change local secondary structures... and possibly the whole folding of the protein, which could be detrimental to its activity/affinity/binding etc...
To choose high enantiomeric purity amino acids gives you a better control on what is happening at this level, and can of course facilitate purification and get a better yield. It's worth it !
Good luck with your project.
If you epimerize one of the aminoacids of the original protein when doing your reaction, you can change the activity of the original protein and you do not want that. You should avoid very basic or acid conditions in your reaction.
If you are making a 10 amino acid protein that's 90% enantiopure in each amino acid, the expected fraction of enantiopure proteins would be 0.9^10, or 35%. That means that you would expect 65% of your proteins to contain a D-amino acid, leading to misfolding or inactive proteins. The efficiency of incorporating each amino acid has compounds the effect - giving you less than full length proteins with the incorrect stereochemistry.
Since you are going to work with (I assume) L-serine it should be of high enantiomeric purity in order to have the correct configuration of the protein you are seeking since if the enantiomeric purity of L-serine is low the D-serine will result in the formation of a protein with different configuration and activity too which will affect your results drastically. Enantiomeric purity is a crucial issue not only in protein synthesis but also in asymmetric synthesis using chiral pool compounds.
If you are using a biological synthesis I doubt if D-amino acids would be incorporated but they might well block receptors, inhibit the polymerase and prevent synthesis.
Enantiomeric purity of amino acids is curtail for getting a protein in a proper configuration and with correct stereochemistry. In addition, this is a condition necessary for avoiding misfolding. Note that the problem of enantiomeric purity of amino acids has an important evolutionary aspect, see the attached references.
If you are planning to derivatise serine to convert it to an azide functionality, either before incorporating it within your protein, or in situ within the protein, be aware that most reactions have a high probability of racemising the serine residue (making it a mixure of L- and D-enantiomers) as they often proceed via a dehydrolalanine intermediate. Azidoalanine is available commercially.
As proteins are chiral molecules able to recognise chiral ligands in a stereo/enantiospecific manner, it is essential to have enantiopure amino acids (serine in your case) to assure a good folding, recognition and reactivity. I highly recommend to pay more for a good purity (>99%) to assure correct addition of functionalities on your protein.
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