Molecular properties and activity of amino-terminal truncated forms of lipase activator protein

Two mutant forms, which had truncated N-terminals, of lipase activator protein (LipB) from Pseudomonas aeruginosa TE3285 were prepared, and their molecular properties and activity were compared with those of the full-length form. A truncated LipB lacking its hydrophobic N-terminal 21 residues was dispersed homogeneously in solution, and could reactivate the stoichiometric amount of denatured lipase. In contrast, full-length LipB formed soluble aggregates, and reactivated less than an equimolar amount of the lipase even under the most suitable conditions. These findings suggest that some or all of the N-terminal 21 residues caused aggregation of the protein molecules, and prevented LipB from fully stoichiometric reactivation. A truncated LipB lacking the N-terminal 61 residues also reactivated denatured lipase, suggesting that the N-terminal 61-residue region of LipB is not involved in reactivation.