Insights into the substrate specificity of plant peptide deformylase, an essential enzyme with potential for the development of novel biotechnology applications in agriculture

The crystal structure of AtPDF1B [Arabidopsis thaliana PDF (peptide deformylase) 1B; EC 3.5.1.88], a plant specific deformylase, has been determined at a resolution of 2.4 Å (1 Å=0.1 nm). The overall fold of AtPDF1B is similar to other peptide deformylases that have been reported. Evidence from the crystal structure and gel filtration chromatography indicates that AtPDF1B exists as a symmetric dimer. PDF1B is essential in plants and has a preferred substrate specificity towards the PS II (photosystem II) D1 polypeptide. Comparative analysis of AtPDF1B, AtPDF1A, and the type 1B deformylase from Escherichia coli, identifies a number of differences in substrate binding subsites that might account for variations in sequence preference. A model of the N-terminal five amino acids from the D1 polypeptide bound in the active site of AtPDF1B suggests an influence of Tyr¹⁷⁸ as a structural determinant for polypeptide substrate specificity through hydrogen bonding with Thr² in the D1 sequence. Kinetic analyses using a polypeptide mimic of the D1 N-terminus was performed on AtPDF1B mutated at Tyr¹⁷⁸ to alanine, phenylalanine or arginine (equivalent residue in AtPDF1A). The results suggest that, whereas Tyr¹⁷⁸ can influence catalytic activity, other residues contribute to the overall preference for the D1 polypeptide.