In most cases, you will NOT choose the pH for buffers based on a protein's isoelectric point. Instead, many recombinant proteins are purified by affinity tags, where the buffer composition and pH are optimized for the particular affinity chromotography application.
When the pH=pI for a given protein, that protein will carry no net charge and will be minimally soluble in non-denaturing aqueous conditions. This will tend to promote protein precipitation. In some circumstances, selective precipitation can be used as a means to purify proteins, but this strategy is not commonly employed for recombinant proteins. Instead, one will typically select a pH that promotes protein solubility, which is typically far from the pI of your target protein.
In most cases, you will NOT choose the pH for buffers based on a protein's isoelectric point. Instead, many recombinant proteins are purified by affinity tags, where the buffer composition and pH are optimized for the particular affinity chromotography application.
When the pH=pI for a given protein, that protein will carry no net charge and will be minimally soluble in non-denaturing aqueous conditions. This will tend to promote protein precipitation. In some circumstances, selective precipitation can be used as a means to purify proteins, but this strategy is not commonly employed for recombinant proteins. Instead, one will typically select a pH that promotes protein solubility, which is typically far from the pI of your target protein.