EXPRESSION OF RECOMBINANT RAT MYOINOSITOL 1,4,5-TRISPHOSPHATE 3-KINASE-B SUGGESTS A REGULATORY ROLE FOR ITS N-TERMINUS

We have expressed rat myo-inositol 1,4,5-trisphosphate (IP3) 3-kinase B as both a full-length, recombinant, non-fusion protein and a full-le ngth, recombinant, fusion protein with maltose-binding protein (MBP) i n Escherichia coli. The fusion protein with MBP is soluble, binds calm odulin and is enzymically active whereas the non-fusion protein is ins oluble and does not bind calmodulin unless co-expressed with bacterial chaperone proteins (either GroES and GroEL, or DnaK, DnaJ and GrpE). However, soluble, calmodulin-binding non-fusion IF3 3-kinase B is enzy mically inactive. The catalytic domain of the enzyme has previously be en shown to reside near the C-terminus; the results we present suggest an auto-regulatory role for the N-terminus.