High level expression of a synthetic gene coding for IgG-binding domain B of Staphylococcal protein A

A gene coding for one of the IgG-binding domains of Staphylococcalprotein A, designated domain B, was chemically synthesized.This gene was tandemly repeated to give dimeric and tetramericdomain B genes by the use of two restriction enzymes which gaveblunt ends. The genes were highly expressed in Escherichia colito afford a large amount of dimeric and tetrameric domain Bproteins. The single domain B protein was efficiently producedas a fusion protein with a salmon growth hormone fragment. Thefusion protein was converted to monomeric domain B by cyanogenbromide cleavage. The CD spectra of the monomeric, dimeric andtetrameric domain B proteins were essentially the same as thatof native form protein A, showing that their secondary structureswere very similar. The dimeric and tetrameric domain B proteinsformed precipitates with IgG as protein A. This system permitsthe efficient production of mutated single and multiple IgG-bindingdomains which can be used to study structural changes and proteinA–immunoglobulin interactions.