Preparation and Characterization of Fully Active Biotinylated Analogs of Phytosulfokine-α

We report the preparation of biotinylated analogs of phytosulfokine-α (Tyr(SO3H)-Ile-Tyr(SO3H)-Thr-Gln; PSK-α), an endogenous peptide growth factor in plants. Because the modification of the N-terminal amino group leads to significant loss of the activities, a Lys residue was incorporated in the C-terminal region of PSK-α, and its e amino group was reacted with biotinylation reagent. Results of the binding assay showed that [N(ε)-(biotinyl)Lys(5)]PSK-α retained the same binding activity and mitogenic activity as that of native PSK-α. Insertion of a single or double 6-aminohexanoic acid spacer between the ε amino group of Lys(5) and the carboxyl group of biotin did not significantly alter the activities of biotinylated [Lys(5)]PSK-α. Structure-activity information obtained here would be useful for the detection and isolation of PSK-α receptors.