Design, synthesis, expression, and characterization of the genes for mouse Fc gamma RIIb1 and Fc gamma RIIb2 cytoplasmic regions.

The cytoplasmic regions of the mouse low-affinity Fc gamma RII isoforms, mFc gamma RIIb1, and mFc gamma RIIb2, play a key role in signal transduction by mediating different cellular functions. mFc gamma RIIb1 has a 94-residue cytoplasmic region, whereas mFc gamma RIIb2 has a 47-residue cytoplasmic region. Genes encoding the cytoplasmic regions of mFc gamma RIIb1 (b1-94) and mFc gamma RIIb2 (b2-47) were designed, synthesized, and expressed as fusion proteins in Escherichia coli. A sequence-specific protease, thrombin, was used to release the b1-94 peptide, which was purified by using HPLC. The b2-47 peptide was synthesized chemically. CD spectropolarimetry was employed to examine the secondary structures of b1-94 and b2-47. These studies were conducted in aqueous solution, in mixtures of water and trifluoroethanol or methanol, and as a function of temperature. The results indicate that the b1-94 and b2-47 structures are sensitive functions of the solvent environment, and that nonaqueous solvents induce significant alpha-helical structure.