I am working on the methylation of different plant-based proteins, such as canola meal proteins and soy meal proteins. It was mentioned in literature that methyl esterifications shift the isoelectric pH of proteins towards the alkaline range. However, after methylation the solubility of proteins becomes significantly low. How can one increase the solubility of proteins?
Hi Dhillon,
Performing methylation at relatively lower concentration (1-2mg/ml) can eliminate aggregation. If, however, upon completion of the process and exchanging back to the original buffer you notice aggregation, I would suggest adding glycerol (up to 10%), L-arginine (titrated to the buffer of choice) or playing with the pH, meaning in the case you suggested, increasing it even further. You can always evaluate lower pH values (under the pI of the protein) assuming this value is not @ below pH 5.
Good luck!
Chen
Dear Dhillon,
Solubility of a protein depends on amount of free hydrophilic and charged groups in side chains of amino acid residues in the protein. Methylation takes place through OH-groups leading to increase in hydrophobicity of the protein. At isoelectric point (pI) total amount of positively charged groups is equal to that of negatively charged ones, so the summary charge of a protein becomes equal to zero. So at pH of solution equal to pI of a protein the latter becomes insoluble and precipitates. To increase water solubility of your proteins you can change pH value of solution by using of proper buffer. You should take into account pI values of your proteins.
Thanks Guttman and Moldogazieva for your quick responses. Actually my concern is that I want to use the methylated protein at pH above alkaline range (7-9 pH). Going above the isoelectric pH results in protein precipitation, so finding this modified protein not useful.
Any other option to increase its solubility b/w pH 7-9.??
At the first place, it is not clear to me, why you want to methylate the proteins?
@ Randeep_To add more positive charge to the proteins for flocculation purpose.
Methylation will promote hydrophobic surface interactions. An easy experiment is to try a range of lower salt conditions as hydrophobic interactions are increased at high salt.
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