title: Targeting the SH3 domain of human osteoclast-stimulating factor with rationally designed peptoid inhibitors.
abstract: Human osteoclast-stimulating factor (hOSF) is an intracellular protein produced by osteoclasts that induces osteoclast formation and bone resorption. The protein contains a modular Src homology 3 (SH3) domain that mediates the intermolecular recognition and interaction of hOSF with its biological partners. Here, we proposed targeting the hOSF SH3 domain to disrupt hOSF-partner interactions for bone disease therapy by using SH3 inhibitors. In the procedure, the primary sequences of three known hOSF-interacting proteins (c-Src, SMN and Sam68) were parsed, from which totally 31 octapeptide segments that contain the core SH3-binding motif PXXP were extracted, and their binding behavior to hOSF SH3 domain was investigated at structural level using a biomolecular modeling protocol. Several SH3-binding candidates were identified theoretically and then determined to have high or moderate affinity for the domain using fluorescence spectroscopy assays. One potent peptide (425) APPARPVK(432) (Kd  = 3.2 μM), which corresponds to the residues 425-432 of Sam68 protein, was used as template to derive N substitution of peptides (peptoids). Considering that proline is the only endogenous N-substituted amino acid that plays a critical role in SH3-peptide binding, the substitution was addressed at the two key proline residues (Pro427 and Pro430) of the template peptide with nine N-substituted amino acid types. By systematically evaluating the structural and energetic effects of different N-substituted amino acids presenting at the two proline sites on peptide binding, we rationally designed five peptoid inhibitors and then determined in vitro their binding affinity to hOSF SH3 domain. Consequently, two designed peptoids APPAR(N-Clp)VK and APPAR(N-Ffa)VK with Pro430 replaced by N-Clp and N-Ffa were confirmed to have increased (Kd  = 0.87 μM) and comparable (Kd  = 2.9 μM) affinities relative to the template, respectively. In addition, we also found that the Pro427 residue plays an essential role in restricting peptide/peptoid conformations to polyproline II (PPII) helix as the basic requirement of SH3 binding so that the residue cannot be modified. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.
authors.affiliation: Department of Orthopedics, Shandong Provincial Hospital, Jinan, 250021, China.
authors.forename: Shijie
authors.initials: S
authors.lastname: Han
authors.affiliation: Department of Pain Management, Qilu Hospital of Shandong University, Jinan, 250012, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Department of Orthopedics, Shandong Provincial Hospital, Jinan, 250021, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Wang
authors.affiliation: Department of Orthopedics, Shandong Provincial Hospital, Jinan, 250021, China.
authors.forename: Zenong
authors.initials: Z
authors.lastname: Yuan
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001665:Binding Sites; D050071:Bone Density Conservation Agents / Q000138:chemical synthesis / Q000737:chemistry*; D000081247:CSK Tyrosine-Protein Kinase; D004268:DNA-Binding Proteins / Q000737:chemistry; D015195:Drug Design; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D007700:Kinetics; D008024:Ligands; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D034444:Peptoids / Q000138:chemical synthesis / Q000737:chemistry*; D011392:Proline / Q000737:chemistry*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry; D016601:RNA-Binding Proteins / Q000737:chemistry; D013329:Structure-Activity Relationship; D055533:Survival of Motor Neuron 1 Protein / Q000737:chemistry; D013816:Thermodynamics; D018909:src Homology Domains; D019061:src-Family Kinases / Q000737:chemistry
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D050071:Bone Density Conservation Agents; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; C489559:KHDRBS1 protein, human; D008024:Ligands; C118408:OSTF1 protein, human; D010455:Peptides; D034444:Peptoids; D011506:Proteins; D016601:RNA-Binding Proteins; C526471:SMN1 protein, human; D055533:Survival of Motor Neuron 1 Protein; C011083:polyproline; D011392:Proline; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human
keywords: N-substituted amino acid; SH3 domain; bone; osteoclast-stimulating factor; peptide; peptoid