title: Structure and activity of CPNGRC: a modified CD13/APN peptidic homing motif.
abstract: Asn-Gly-Arg peptides have been designed as vehicles for the delivery of chemotherapeutics, magnetic resonance imaging contrast agents, and fluorescence labels to tumor cells, and cardiac angiogenic tissue. Specificity is derived via an interaction with aminopeptidase N, also known as CD13, a cell surface receptor that is highly expressed in angiogenic tissue. Peptides containing the CNGRC homing sequence tethered to a pro-apoptotic peptide sequence have the ability to specifically induce apoptosis in tumor cells. We have now identified a modification to the Asn-Gly-Arg homing sequence motif that improves overall binding affinity to aminopeptidase N. Through the addition of a proline residue, the new peptide with sequence, CPNGRC, inhibits aminopeptidase N proteolytic activity with an IC(50) of 10 microM, a value that is 30-fold lower than that for CNGRC. Both peptides are cyclized via a disulfide bridge between cysteines. Steady-state kinetic experiments suggest that efficient aminopeptidase N inhibition is achieved through the highly cooperative binding of two molecules of CPNGRC. We have used NMR-derived structural constraints for the elucidation of the solution structures CNGRC and CPNGRC. Resulting structures of CNGRC and CPNGRC have significant differences in the backbone torsion angles, which may contribute to the enhanced binding affinity and demonstrated enzyme inhibition by CPNGRC.
authors.affiliation: Department of Biology, University of San Diego, San Diego, CA 92110, USA. lplesniak@gmail.com
authors.forename: Leigh A
authors.initials: LA
authors.lastname: Plesniak
authors.forename: Bridget
authors.initials: B
authors.lastname: Salzameda
authors.forename: Holly
authors.initials: H
authors.lastname: Hinderberger
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Regan
authors.forename: James
authors.initials: J
authors.lastname: Kahn
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Mills
authors.forename: Peter
authors.initials: P
authors.lastname: Teriete
authors.forename: Yong
authors.initials: Y
authors.lastname: Yao
authors.forename: Patricia
authors.initials: P
authors.lastname: Jennings
authors.forename: Francesca
authors.initials: F
authors.lastname: Marassi
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Adams
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017209:Apoptosis; D018826:CD13 Antigens / Q000037:antagonists & inhibitors* / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D010455:Peptides / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D008024:Ligands; D010455:Peptides; D018826:CD13 Antigens