Biochemical characterization of atypical biotinylation domains in seed proteins

Homologues of the pea SBP65, a late embryogenesis abundant (LEA) biotinylat ed protein that behaves as a putative sink for the free vitamin biotin duri ng embryo development, were characterized biochemically in various plant sp ecies, including soybean, lentil, peanut, rape, cabbage, carrot and sugarbe et. Based on sequence homologies, the genome of Arabidopsis thaliana contai ns a gene putatively encoding a homologue of pea SBP65. These proteins exhi bit two remarkable features. First, they only accumulate in seeds, particul arly during late stages of embryo development. The results strongly suggest that these seed-specific biotinylated proteins belong to the class of plan t proteins called seed maturation proteins, which are presumed to play majo r roles in embryo development. Secondly, covalent attachment of biotin occu rs at a lysine residue within a conserved motif of (V/M)GKF, which shows no resemblance to the highly conserved AMKM tetrapeptide that houses the targ et lysine residue in the well-characterized biotin-dependent carboxylases a nd decarboxylases. These findings highlight novel structural features for p rotein biotinylation.