Calcium Binding Protein 39 (CABP39)

The deduced 341-amino acid protein shares a high degree of conservation with its C. elegans and Drosophila orthologs. Northern blot analysis detected a 4.2-kb MO25-alpha transcript in all tissues examined, with highest expression in skeletal muscle. Endogenous MO25-alpha in HeLa cells had an apparent molecular mass of 40 kD by SDS-PAGE. Cotransfection and mutation analysis revealed that MO25-alpha interacted directly with STRAD-alpha rather than with LKB1, and the interaction required the last 3 residues of STRAD-alpha. MO25-alpha also interacted with STRAD-beta (ALS2CR2) in a complex with LKB1. MO25-alpha and STRAD-alpha anchored LKB1 in the cytoplasm, excluding it from the nucleus. Moreover, MO25-alpha enhanced formation of LKB1-STRAD-alpha complexes in vivo and stimulated LKB1 catalytic activity about 10-fold.