Immune response to the collagen-like synthetic ordered polypeptide (L-Pro-Gly-L-Pro)n

Clickable Polyprolines from Azido-proline N-Carboxyanhydride

Polyproline is a material of great interest in biomedicine due to its helical scaffold of structural importance in collagen and mucins and its ability to gel and to change conformations in response to temperature. Appending of function-modulating chemical groups to such a material is desirable to diversify potential applications. Here, we describe the synthesis of high-molecular-weight homo, block, and statistical polymers of azide-functionalized proline. The azide groups served as moieties for highly efficient click-grafting, as stabilizers of the polyproline PPII helix, and as modulators of thermoresponsiveness. Saccharides and ethylene glycol were utilized to explore small-molecule grafting, and glutamate polymers were utilized to form polyelectrolyte bottlebrush architectures. Secondary structure effects of both the azide and click modifications, as well as lower critical solution temperature behavior, were characterized. The polyazidoprolines and click products were well tolerated by live human cells and are expected to find use in diverse biomedical applications.

Rethinking Transition Metal Catalyzed N-Carboxyanhydride Polymerization: Polymerization of Pro and AcOPro N-Carboxyanhydrides

Polyproline (PP) based polypeptides have broad applications as protein mimics, ordered materials, hydrogels, and surface coatings. However, a lack of rapid and efficient preparatory methods has challenged synthesis of well-defined high molecular weight materials. Here, we report facile and high-yielding methods for preparation and polymerization of Pro and trans-4-acetoxy-Pro N-carboxyanhdrides (NCAs). For decades, transition metal initiators of NCA polymerization were assumed to be nonstarters with Pro due to the lack of an amide NH proton. We carefully considered the known steps in the initiation mechanism and applied a Ni initiator that intercepts an intermediate and does not require an NH group. This initiator efficiently catalyzes controlled, living polymerization of Pro NCAs, revealing that routes alternate to the previously proposed mechanism must be at play. We also found Co species can catalyze Pro NCA polymerization, and we improved the synthetic methods to prepare the NCA monomers. Our methods are high-yielding and rapid and give tunable, end-functional PP-based homo, statistical, and block polypeptides. We characterized the conformation of PP and trans-4-hydroxy-PP by CD and confirmed the time scale for quantitative conversion from PPI to PPII helices. Overall, our data shed light on the general propagation mechanism of transition metal catalyzed NCA polymerization and have opened the door for efficient preparation of a desirable class of biomaterials.

Immunoassay for honey bee cytochrome c in single animals with cytochrome c-coated bacteriophages: a sensitive tool for the study of caste formation in the honey bee, Apis mellifera

The development of a sensitive viroimmunoassay for honey bee cytochrome c and its usage for early detection of caste differentiation is described. Pure honey bee cytochrome c was isolated from workers and used to produce antibodies in rabbits. Bacteriophage T4 was chemically modified by covalent attachment of honey bee cytochrome c using tolylene-2,4-diisocyanate as a cross-linking agent. The immunospecific inactivation of this bacteriophage-cytochrome c conjugate by anti-cytochrome c antibodies can be inhibited by free cytochrome c. In quantitative determinations, 50% inhibition is reproducibly achieved at a concentration of 6 ng/ml (5 pmol/ml) and as little as 0.3 ng/ml (0.25 pmol/ml) could be detected by this system. Cytochrome c concentrations were measured in individual animals and substantial differences corresponding larval stages of worker and queen bees are reported.

The effect of the thymus-independent antigens, collagen and synthetic collagen-like polypeptide, on the requirement of cell cooperation in the immune response to thymus-dependent antigens

The effect of thymus-independent antigens on the need for cell cooperation in the immune response to thymus-dependent antigens was investigated. Irradiated recipient mice transplanted with either bone marrow cells or a mixture of bone marrow and thymus cells, were immunized with the thymus-independent antigen (Pro-Gly-Pro)n covalently conjugated to the thymus-dependent ovalbumin, or with a mixture of (Pro-Gly-Pro)n and ovalbumin. In both cases an effective response towards ovalbumin was observed in the absence of thymus cells as was found for the thymus-independent (Pro-Gly-Pro)n. The same effect on ovalbumin was demonstrated when a mixture of the thymus-independent collagen and ovalbumin was used for immunization. On the other hand, when irradiated reconstituted mice were immunized with a mixture of ovalbumin and the thymus-dependent gelatin, which is the denatured product of collagen, cell-to-cell cooperation was required for an immune response to both immunogens. The effect of (Pro-Gly-Pro)n and collagen on the response to the thymus-dependent ovalbumin in vivo was observed in in vitro experiments using sheep red blood cells (SRBC) as the immunogen as well. In the presence of reduced and carboxymethylated (RCM) Ascaris collagen and (Pro-Gly-Pro)n, nude spleen cells could produce significant numbers of plaque-forming cells towards SRBC. Thus, (Pro-Gly-Pro)n and collagen can deliver the signal required to stimulate B cells to produce antibody towards thymus-dependent antigens in the absence of T cells. In contrast to the results with (Pro-Gly-Pro)n and collagen, the thymus-independent synthetic polypeptide poly(DTyr, DGlu-)-poly(DPro)--poly(DLys) did not affect the requirement for cell cooperation of the thymus-dependent immunogens, ovalbumin and SRCB. It thus appears that the ability to substitute for T cells for antibody production towards thymus-dependent immunogens is not a general characteristic of thymus-independent antigens.

Thymus independence of a collagen-like synthetic polypeptide and of collagen, and the need for thymus and bone marrow-cell cooperation in the immune response to gelatin

Several inbred mouse strains were screened for their ability to respond to the ordered periodic collagen-like polymer (Pro-Gly-Pro)(n), to the random copolymer (Pro(66), Gly(34))(n), to the protein conjugate Pro-Gly-Pro-ovalbumin, to rat tail tendon collagen, rat tail tendon gelatin, and to Ascaris cuticle collagen. Differences were obtained in the magnitude of the antibody titers towards the above immunogens among the strains tested. The level of the response to the ordered polymer (Pro-Gly-Pro)(n) was not similar to that towards the random (Pro(66), Gly(34))(n), confirming differences in the antigenic determinants of the two immunogens. The role of the thymus in the immune response to (Pro-Gly-Pro)(n) and (Pro(66), Gly(34))(n) as well as to two collagens and gelatin, was studied in order to find out a possible correlation with the structural features of the immunogens. Heavily irradiated recipients were injected with syngeneic thymocytes, marrow cells, or a mixture of both cell populations and were immunized with the above-mentioned antigens. An efficient immune response to the ordered collagen-like (Pro-Gly-Pro)(n) was obtained in the absence of transferred thymocytes. The thymus independence of (Pro-Gly-Pro)(n) was confirmed when thymectomized irradiated mice were used as recipients. In contrast with these results, cooperation between thymus and marrow cells was necessary in order to elicit an immune response to (Pro(56), Gly(34))(n). Similarly, the immune response to the triple helical collagen was found to be independent of the thymus, whereas for an effective response to its denatured product, gelatin, thymus cells were required. These findings indicate that a unique three-dimensional structure of immunogens possessing repeating antigenic determinants plays an important role in determining the need for cell to cell interaction in order to elicit an antibody response.