Mabel A. Cejas

Thrombogenic collagen-mimetic peptides: Self-assembly of triple helix-based fibrils driven by hydrophobic interactions

Collagens are integral structural proteins in animal tissues and play key functional roles in cellular modulation. We sought to discover collagen model peptides (CMPs) that would form triple helices and self-assemble into supramolecular fibrils exhibiting collagen-like biological activity without preorganizing the peptide chains by covalent linkages. This challenging objective was accomplished by placing aromatic groups on the ends of a representative 30-mer CMP, (GPO)10, as with l-phenylalanine and l-pentafluorophenylalanine in 32-mer 1a. Computational studies on homologous 29-mers 1a′–d′ (one less GPO), as pairs of triple helices interacting head-to-tail, yielded stabilization energies in the order 1a′ > 1b′ > 1c′ > 1d′, supporting the hypothesis that hydrophobic aromatic groups can drive CMP self-assembly. Peptides 1a–d were studied comparatively relative to structural properties and ability to stimulate human platelets. Although each 32-mer formed stable triple helices (CD) spectroscopy, only 1a and 1b self-assembled into micrometer-scale fibrils. Light microscopy images for 1a depicted long collagen-like fibrils, whereas images for 1d did not. Atomic force microscopy topographical images indicated that 1a and 1b self-organize into microfibrillar species, whereas 1c and 1d do not. Peptides 1a and 1b induced the aggregation of human blood platelets with a potency similar to type I collagen, whereas 1c was much less effective, and 1d was inactive (EC50 potency: 1a/1b ≫ 1c > 1d). Thus, 1a and 1b spontaneously self-assemble into thrombogenic collagen-mimetic materials because of hydrophobic aromatic interactions provided by the special end-groups. These findings have important implications for the design of biofunctional CMPs.

Tight inclusion complexation of 2,7-dimethyldiazapyrenium in cucurbit[7]uril

The dicationic guest 2,7-dimethyldiazapyrenium is bound inside the host cucurbit[7]uril, forming a very stable inclusion complex in which the host undergoes structural distortions to accommodate the guest.

A Unique Mucin Immunoenhancing Peptide with Antitumor Properties

Implantation of DA-3 mammary tumor cells into BALB/c mice results in tumor growth, metastatic lesions, and death. These cells were transfected with genes encoding for either the transmembrane (DA-3/TM) or secreted (DA-3/sec) form of human mucin 1 (MUC1). Although the gene for the secreted form lacks the transmembrane and cytoplasmic domains, the 5′ sequences of these mucins are identical; however, the gene for the secreted mucin isoform ends with a sequence encoding for a unique 11 amino acid peptide. The DA-3/TM or DA-3 cells transfected with the neomycin vector only (DA-3/neo) have the same in vivo growth characteristics as the parent cell line. In contrast, DA-3/sec cells fail to grow when implanted in immunocompetent BALB/c animals. DA-3/sec cells implanted in nude mice resulted in tumor development verifying the tumorigenic potential of these cells. Pre-exposure of BALB/c mice to DA-3/sec cells afforded protection against challenge with DA-3/TM or DA-3/neo mammary tumors and the unrelated tumors K7, an osteosarcoma, and RENCA, a renal cell carcinoma. Partial protection against subsequent tumor challenges was also achieved by substituting the 11 amino acid peptide found only in the secreted MUC1 isoform, for the live DA-3/sec cells. Notably, the efficacy of this peptide is not strain restricted because it also retarded the growth of Lewis lung carcinoma cells in C57 BL/6 mice. These findings reveal that a unique peptide present in the secreted MUC1 has immunoenhancing properties and may be a potential agent for use in immunotherapy.