Purification of recombinantly expressed human cluster determinant 4 cytoplasmic domain

A DNA fragment coding for the human CD4 cytoplasmic domain (residues 394–433) was cloned into the pET15b expression vector. The resulting plasmid was used for synthesis of the polyhistidine-tagged 5·103 Mr CD4 peptide in Escherichia coli BL21(DE3)Star. The CD4 cytoplasmic domain was purified under denaturing and reducing conditions by a two-step procedure using immobilized metal affinity chromatography and gel permeation chromatography. The purified CD4 cytoplasmic domain is soluble and functional without any specific refolding steps. The yield of the described purification procedure was ∼5 mg peptide per liter culture volume.