Large-scale expression and purification of a soluble form of the pleckstrin homology domain of the human protooncogenic serine/threonine protein kinase PKB (c-akt) in Escherichia coli.

The protooncogenic serine/threonine protein kinase PKB contains an amino-terminal pleckstrin homology (PH) domain which binds phosphatidylinositides. The PH domain, composed of approximately 100 loosely conserved amino acids, is found in many proteins, including kinases, phospholipases C, GTPases, GTPase-activating proteins, GTPase-exchange factors, "adaptor" proteins, cytoskeletal proteins, and kinase substrates. We have developed an expression system in Escherichia coli that can produce large quantities of a soluble form of the PKB PH domain and have purified it to apparent homogeneity. Expression of the PKB PH domain as a (His)(6)-tagged fusion with the addition of 3 lysines at the carboxyl-terminus facilitated the production of soluble protein. Induction of expression at 24 degrees C as opposed to 37 degrees C also significantly increased solubility of the PH domain. Large-scale purification was easily achieved by exploiting the (His)(6) tag and the high isoelectric point of the protein attributable to the additional 3 carboxyl-terminal lysines. Copyright 1999 Academic Press.