Preparation and crystal structure of the recombinant alpha(1)/alpha(2) catalytic heterodimer of bovine brain platelet-activating factor acetylhydrolase Ib

The intracellular form of mammalian platelet activating factor acetylhydrol ase found in brain (PAF-AH Ib) is thought to play a critical role in contro l in neuronal migration during cortex development. This oligomeric complex consists of a homodimer of the 45 kDa (beta) LIS1 protein, the product of t he causative gene for type I lissencephaly, and, depending on the developme ntal stage and species, one of three possible pairs of two homologous simil ar to 26 kDa alpha -subunits, which harbor all of the catalytic activity. T he exact composition of this complex depends on the expression patterns of the alpha (1) and alpha (2) genes, exhibiting tissue specificity and develo pmental control. All three possible dimers (alpha (1)/alpha (1), alpha (1)/ alpha (2) and alpha (2)/alpha (2)) were identified in tissues. The alpha (1 )/alpha (2) heterodimer is thought to play an important role in fetal brain . The structure of the alpha (1)/alpha (1) homodimer was solved earlier in our laboratory at 1.7 Angstrom. We report here the preparation of recombina nt alpha (1)/alpha (2) heterodimers using a specially constructed bi-cistro nic expression vector. The approach may be useful in studies of other syste ms where pure heterodimers of recombinant proteins are required. The alpha (1)/alpha (2) dimer has been crystallized and its structure was solved at 2 .1 Angstrom resolution by molecular replacement. These results set the stag e for a detailed characterization of the PAF-AH lb complex.