title: Design and NMR characterization of active analogues of compstatin containing non-natural amino acids.
abstract: We present new findings in our drug discovery effort to develop an anticomplement therapeutic. We have designed several active analogues of compstatin by altering its amino acid composition at positions 4 and 9. The most effective analogues have tryptophan or fused-ring non-natural amino acids at position 4 and alanine or an unbranched single-methyl amino acid at position 9. Twenty-one of these analogues have 2-99-fold higher activities compared to the parent peptide compstatin. The analogue Ac-V4(2Nal)/H9A-NH(2) has the highest inhibitory activity with IC(50) 500 nM. NMR data, through NOE and chemical shift analysis, suggest the presence of interconverting conformers spanning the extended and helical regions of the Ramachandran plot, and they detect a predominant averaged conformer with coil structure and at least one flexible beta-turn, of type I. The fused-ring non-natural amino acids at position 4 contribute to the formation of the hydrophobic cluster of compstatin, which has been previously proposed, together with the beta-turn and a disulfide bridge, to be essential for binding to the target of compstatin, complement component C3. We propose that additional mechanisms may contribute to the structural stability of the analogues and to binding to C3, involving intra- and intermolecular electrostatic interactions of the pi-electron system of side chain aromatic rings. The presence of pi-pi interactions for Trp4-Trp7 was confirmed with a molecular dynamics simulation for the most active analogue with natural amino acids, Ac-V4W/H9A-NH(2). Alanine or aminobutyric acid at position 9 contribute to the weak propensity for helical structure of the residue segment 4-10 of the analogues, which may also play a role in increased activity.
authors.affiliation: Department of Chemical and Environmental Engineering, University of California at Riverside, California 92521, USA.
authors.forename: Buddhadeb
authors.initials: B
authors.lastname: Mallik
authors.forename: Madan
authors.initials: M
authors.lastname: Katragadda
authors.forename: Lynn A
authors.initials: LA
authors.lastname: Spruce
authors.forename: Caterina
authors.initials: C
authors.lastname: Carafides
authors.forename: Christos G
authors.initials: CG
authors.lastname: Tsokos
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Morikis
authors.forename: John D
authors.initials: JD
authors.lastname: Lambris
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D001665:Binding Sites; D002478:Cells, Cultured; D015195:Drug Design; D004353:Drug Evaluation, Preclinical / Q000379:methods; D006801:Humans; D020128:Inhibitory Concentration 50; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010456:Peptides, Cyclic / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D011487:Protein Conformation; D013329:Structure-Activity Relationship
chemical_list: D000596:Amino Acids; D010456:Peptides, Cyclic; C111828:compstatin