We have successfully expressed an active variant of recombinant murine GIP (rmGIP) with the N-terminal domain deletion (Delta N-rmGIP) in E. coli Rosetta(DE3)-RIPL cells. Whereas Delta N-rmGIP could be purified under native conditions, the purification of full-length rmGIP required denaturing conditions; and the yields were 31.4 mg and 7.4 mg per L of culture, respectively. Purity was at least 97% as assessed by HPLC. Both proteins exhibited a well-defined secondary structure composition as determined by circular dichroism spectroscopy, with a slightly higher ratio of helical and strand components in Delta N-rmGIP. The phosphatase activity of both proteins was Mg2+-dependent, with a pK(Mg) of activation being similar to 2.8 and non-cooperative binding. The Golli-myelin basic protein isoform rmBG21 (recombinant murine form) enhanced the phosphatase activity of Delta N-rmGIP below 6 mu M, but significantly inhibited it at higher concentrations. Using glutaraldehyde cross-linking and gel shift assays, the rmBG21-Delta N-rmGIP interaction was shown to be equimolar and specific, but seemingly relatively weak, suggesting that a third interaction partner is required in vivo. (C) 2008 Elsevier Inc. All rights reserved.