Preparation and crystal structure of the recombinant α1/α2 catalytic heterodimer of bovine brain platelet-activating factor acetylhydrolase Ib

The intracellular form of mammalian platelet activating factor acetylhydrolase found in brain (PAF-AH Ib) is thought to play a critical role in control in neuronal migration during cortex development. This oligomeric complex consists of a homodimer of the 45 kDa (β) LIS1 protein, the product of the causative gene for type I lissencephaly, and, depending on the developmental stage and species, one of three possible pairs of two homologous ~26 kDa α-subunits, which harbor all of the catalytic activity. The exact composition of this complex depends on the expression patterns of the α1 and α2 genes, exhibiting tissue specificity and developmental control. All three possible dimers (α1/α1, α1/α2 and α2/α2) were identified in tissues. The α1/α2 heterodimer is thought to play an important role in fetal brain. The structure of the α1/α1 homodimer was solved earlier in our laboratory at 1.7 A. We report here the preparation of recombinant α1/α2 heterodimers using a specially constructed bi-cistronic expression vector. The approach may be useful in studies of other systems where pure heterodimers of recombinant proteins are required. The α1/α2 dimer has been crystallized and its structure was solved at 2.1 A resolution by molecular replacement. These results set the stage for a detailed characterization of the PAF-AH Ib complex.