Polymeric ADAM protein mimics interrogate mammalian sperm-egg binding

Precision Synthesis of Alternating Copolymers via Ring-Opening Polymerization of 1-Substituted Cyclobutenes

Investigation of complex molecular systems depends on our ability to correlate physical measurements with molecular structure. Interpretation of studies that rely on synthetic polymers is generally limited by their heterogeneity; i.e., there is variation in the number and arrangement of the monomeric building blocks that have been incorporated. Superior physics and biology can be performed with materials and tools that exert precise control over the sequence and spacing of functional groups. An interest in functional ligands combined with a desire to control the orientation and stereochemistry of monomer incorporation led to the design of new substrates for ruthenium-catalyzed ring-opening metathesis polymerization (ROMP). We discovered that ROMP of cyclobutene-1-carboxamides provides uniform and translationally invariant polymers. In contrast, cyclobutene-1-carboxylate esters ring open upon treatment with ruthenium catalyst, but they are stable to homopolymerization. However, in the presence of cyclohexene monomers, they undergo alternating ROMP (AROMP or alt-ROMP) to give copolymers with a precisely controlled sequence. The alternating cyclobutene ester/cyclohexene pair provides access to functional group spacing larger than is possible with homopolymers. This can be desirable; for example, polymers with a regular 8-10 Å backbone spacing of cationic charge and with between four and eight cationic groups were the most effective antibacterial agents and had low cytotoxicity. Moreover, the AROMP chemistry allows alternation of two functional moieties: one associated with the cyclohexene and one attached to the cyclobutene. In the case of antibacterial copolymers, the alternating chemistry allowed variation of hydrophobicity via the cyclohexene while maintaining a constant cation spacing through the cyclobutene. In the case of copolymers that bear donor and acceptor groups, strict alternation of the groups increased intrachain charge transfer. Like cyclobutene-1-carboxylate esters, bicyclo[4.2.0]oct-7-ene-7-carboxylate esters ring open upon treatment with ruthenium catalyst and undergo ring opening cross-metathesis with cyclohexene to form alternating copolymers. The corresponding bicyclo[4.2.0]oct-7-ene-7-carboxyamides isomerize to the bicyclo[4.2.0]oct-1(8)-ene-8-carboxamides before they can ring open. However, the isomerized amides undergo ruthenium-catalyzed ring opening metathesis and rapidly AROMP with cyclohexene. Our alternating copolymer systems allow functionality to be placed along a polymer chain with larger than typical spacing. We have used both homopolymers and alternating copolymers for defining the functional group density required for targeting a cell surface and for the exploration of functional group positioning within a polymer chain. These polymer systems provide access to new materials with previously inaccessible types of nanoscale structures.

Poly(oligonucleotide)

Here we report the preparation of poly(oligonucleotide) brush polymers and amphiphilic brush copolymers from nucleic acid monomers via graft-through polymerization. We describe the polymerization of PNA-norbornyl monomers to yield poly-PNA (poly(peptide nucleic acid)) via ring-opening metathesis polymerization (ROMP) with the initiator, (IMesH2)(C5H5N)2(Cl)2RuCHPh.1 In addition, we present the preparation of poly-PNA nanoparticles from amphiphilic block copolymers and describe their hybridization to a complementary single-stranded DNA (ssDNA) oligonucleotide.

Enhanced potency of the metalloprotease inhibitor TAPI-2 by multivalent display

Metalloproteases regulate a vast array of critical cellular processes such as proliferation, migration, repair, and invasion/metastasis. In so doing, metalloproteases have been shown to play key roles in the pathogenesis of multiple disorders including arteriosclerosis, arthritis, cancer metastasis, and ischemic brain injury. Therefore, much work has focused on developing metalloprotease inhibitors to provide a potential therapeutic benefit against the progression of these and other diseases. In order to produce a more potent inhibitor of metalloproteases, we synthesized multivalent displays of a metalloprotease inhibitor derived from the ring-opening metathesis polymerization (ROMP). Specifically, multivalent ligands of a broad-spectrum metalloprotease inhibitor, TAPI-2, were generated upon conjugation of the amine-bearing inhibitor with the ROMP-derived N-hydroxysuccinimide ester polymer. By monitoring the metalloprotease dependent cleavage of the transmembrane protein Semaphorin4D (Sema4D), we demonstrated an enhancement of inhibition by multivalent TAPI-2 compared to monovalent TAPI-2. To further optimize the potency of the multivalent inhibitor, we systematically varied the polymer length and inhibitor ligand density (mole fraction, χ). We observed that while ligand density plays a modest role in the potency of inhibition caused by the multivalent TAPI-2 display, the length of the polymer produces a much greater effect on inhibitor potency, with the shortest polymer achieving the greatest level of inhibition. These findings validate the use of multivalent display to enhance the potency of metalloprotease inhibitors and further, suggest this may be a useful approach to enhance potency of other small molecule towards their targets.

Role of vitelline envelope during fertilization in the black tiger shrimp, Penaeus monodon

Animal eggs possess investments through which sperm must penetrate. The aim of the present study was to investigate the role of the egg coating, the vitelline envelope, during sperm-egg interactions in the black tiger shrimp, Penaeus monodon. The site(s) of primary binding between sperm and egg and the possible binding molecule(s) for sperm were identified. In vitro adsorption of the vitelline envelope protein onto the sperm surface showed that primary binding occurred between the sperm anterior spike of acrosome intact sperm and the vitelline envelope. Results from streptavidin blotting revealed that the component of the vitelline envelope that interacts with the sperm integral membrane protein is a 370kDa protein. In addition, it was shown that the vitelline envelope protein had no ability to induce acrosome reaction. These results suggest that the function of the vitelline envelope is as a primary binding site for sperm in shrimp, but not a sole trigger for the acrosome reaction.

Architecture effects on L-selectin shedding induced by polypeptide-based multivalent ligands

Multivalent interactions between selectins and their ligands play key roles in mediating the rolling and tethering of leukocytes in the early steps of the inflammatory response, as well as in lymphocyte circulation. L-selectin shedding, which is the proteolytic cleavage of L-selectin, can be induced by L-selectin clustering through the binding of multivalent ligands to multiple L-selectin molecules, and it has been shown to regulate leukocyte rolling and subsequent integrin activation for firm adhesion. In this paper, we report the production of homogenous glycopolypeptides modified with a 3,6-disulfo-galactopyranoside equipped with a caproyl linker. The saccharide residue was chemically attached to various polypeptide backbones of differing architectures; the composition and purity of the sulfated glycopolypeptides was confirmed via¹H-NMR spectroscopy, amino acid analysis (AAA), and electrophoretic analysis. The retention of the conformation of the polypeptide backbone was confirmed via circular dichroic spectroscopy. The shedding of l-selectin from the surface of Jurkat cells induced by these sulfated glycopolypeptides, determined via ELISA-based methods, varied based on differences in the architectures of the polypeptide scaffolds, suggesting opportunities for these strategies in probing cell-surface receptor arrays and directing cell signaling events.

Scope of the ring-opening metathesis polymerization (ROMP) reaction of 1-substituted cyclobutenes

The reactivities of a series of 1-substituted cyclobutene derivatives (carboxylate esters, carboxamides, and carbinol esters) were investigated as substrates for ring-opening metathesis polymerization (ROMP) with [(H(2)IMes)(3-Br-pyridine)(2)(Cl)(2)Ru=CHPh]. Both the secondary amides of 1-cyclobutenecarboxylic acid and the esters of 1-cyclobutene-1-methanol undergo polymerization. The secondary amides provide translationally invariant polymers (E-olefins). Although the carbinol esters yield stereo- and regiochemically heterogeneous polymers, the 1-cyclobutenecarboxylic acid esters and tertiary amides undergo ring-opening metathesis (ROM) but not ROMP. The regio- and stereochemical outcomes of these ROMP and ROM reactions were analyzed at the B3LYP/6-31G* and LANL2DZ levels of theory. Calculations suggest that the regiochemistry and stereochemistry of the addition to the propagating carbene to form the metallocyclobutane intermediate depend on both charge distribution and steric interactions.

Beta1 integrin is an adhesion protein for sperm binding to eggs

We investigated the role of beta(1) integrin in mammalian fertilization and the mode of inhibition of fertilinbeta-derived polymers. We determined that polymers displaying the Glu-Cys-Asp peptide from the fertilinbeta disintegrin domain mediate inhibition of mammalian fertilization through a beta(1) integrin receptor on the egg surface. Inhibition of fertilization is a consequence of competition with sperm binding to the cell surface, not activation of an egg-signaling pathway. The presence of the beta(1) integrin on the egg surface increases the rate of sperm attachment but does not alter the total number of sperm that can attach or fuse to the egg. We conclude that the presence of beta(1) integrin enhances the initial adhesion of sperm to the egg plasma membrane and that subsequent attachment and fusion are mediated by additional egg and sperm proteins present in the beta(1) integrin complex. Therefore, the mechanisms by which sperm fertilize wild-type and beta(1) knockout eggs are different.