Enhancement of antigen-specific CD4+ and CD8+ T cell responses using a self-assembled biologic nanolipoprotein particle vaccine

To address the need for vaccine platforms that induce robust cell-mediated immunity, we investigated the potential of utilizing self-assembling biologic nanolipoprotein particles (NLPs) as an antigen and adjuvant delivery system to induce antigen-specific murine T cell responses. We utilized OT-I and OT-II TCR-transgenic mice to investigate the effects of NLP-mediated delivery of the model antigen ovalbumin (OVA) on T cell activation. Delivery of OVA with the TLR4 agonist monophosphoryl lipid A (MPLA) in the context of NLPs significantly enhanced the activation of both CD4⁺ and CD8⁺ T cells in vitro compared to co-administration of free OVA and MPLA. Upon intranasal immunization of mice harboring TCR-transgenic cells, NLPs enhanced the adjuvant effects of MPLA and the in vivo delivery of OVA, leading to significantly increased expansion of CD4⁺ and CD8⁺ T cells in lung-draining lymph nodes. Therefore, NLPs are a promising vaccine platform for inducing T cell responses following intranasal administration.

Lipid Cross-Linking of Nanolipoprotein Particles Substantially Enhances Serum Stability and Cellular Uptake

Nanolipoprotein particles (NLPs) consist of a discoidal phospholipid lipid bilayer confined by an apolipoprotein belt. NLPs are a promising platform for a variety of biomedical applications due to their biocompatibility, size, definable composition, and amphipathic characteristics. However, poor serum stability hampers the use of NLPs for in vivo applications such as drug formulation. In this study, NLP stability was enhanced upon the incorporation and subsequent UV-mediated intermolecular cross-linking of photoactive DiynePC phospholipids in the lipid bilayer, forming cross-linked nanoparticles (X-NLPs). Both the concentration of DiynePC in the bilayer and UV exposure time significantly affected the resulting X-NLP stability in 100% serum, as assessed by size exclusion chromatography (SEC) of fluorescently labeled particles. Cross-linking did not significantly impact the size of X-NLPs as determined by dynamic light scattering and SEC. X-NLPs had essentially no degradation over 48 h in 100% serum, which is a drastic improvement compared to non-cross-linked NLPs (50% degradation by ∼10 min). X-NLPs had greater uptake into the human ATCC 5637 bladder cancer cell line compared to non-cross-linked particles, indicating their potential utility for targeted drug delivery. X-NLPs also exhibited enhanced stability following intravenous administration in mice. These results collectively support the potential utility of X-NLPs for a variety of in vivo applications.

Use of biologic nanolipoprotein particles containing monophosphoryl lipid A as a novel intranasal vaccine platform for Bacillus anthracis

There is considerable interest in developing a novel Bacillus anthracis vaccine that improves upon the shortcomings of the licensed vaccine for broader, more rapid protection of the population. Ideally, a vaccine would recognize the spore in addition to having anti-toxin effects as well as induce robust mucosal and lung-associated immunity for early recognition and clearance. Here, we investigate nanolipoprotein particles (NLPs) containing the Toll-like receptor 4 agonist monophosphoryl lipid A (MPLA) as a platform for intranasal vaccination against Bacillus anthracis. Modified lipids enabled attachment of disparate spore and toxin protein antigens. Intranasal vaccination of mice with B. anthracis antigen-MPLA-NLP constructs vs. delivery with free MPLA induced robust IgG and IgA responses in serum and in bronchoalveolar and nasal lavage. Typically, a single dose sufficed to induce sustained antibody titers over time. Robust T cell responses to various spore antigens were also detected in the lung. When multiple immunizations were required, specific antibodies were detected earlier in the boost schedule with MPLA-NLP-mediated delivery than with free MPLA. Administering combinations of constructs induced robust responses to all incorporated antigens, indicating potential for a multivalent vaccine preparation. Experiments to determine the efficacy of multivalent vaccine preparations against inhalational B. anthracis challenge are ongoing. In summary, the NLP platform enhances humoral, cellular and mucosal responses to intranasal immunization, indicating promise for NLPs as a flexible, robust vaccine platform against B. anthracis and potentially other inhalational pathogens.

Use of biologic nanolipoprotein particles containing monophosphoryl lipid A as a novel vaccine platform against inhalational pathogens (VAC7P.956)

Subunit vaccines are theoretically safe and easy to manufacture but require effective adjuvants and delivery systems to yield protective immunity, particularly at critical mucosal sites such as the lung. We investigated nanolipoprotein particles (NLPs) containing the Toll-like receptor 4 agonist monophosphoryl lipid A (MPLA) as a platform for intranasal vaccination against Bacillus anthracis. Modified lipids enabled attachment of disparate spore and toxin protein antigens. Intranasal vaccination of mice with B. anthracis antigen-MPLA-NLP constructs vs. delivery with free MPLA induced robust IgG and IgA responses in serum and in bronchoalveolar and nasal lavage. Typically, a single dose sufficed to induce sustained antibody titers over time. When multiple immunizations were required, specific antibodies were detected earlier in the boost schedule with MPLA-NLP-mediated delivery than with free MPLA. Administering combinations of constructs induced responses to multiple antigens, indicating potential for a multivalent vaccine preparation. No off-target responses to the species-matched NLP scaffold protein were detected. Using the ovalbumin/TCR transgenic model, MPLA-NLPs enhanced antigen-specific T cell expansion in lung-draining lymph nodes. In summary, the NLP platform enhances cellular, humoral, and mucosal responses to intranasal immunization, indicating promise for NLPs as a flexible, robust vaccine platform against B. anthracis and potentially other inhalational pathogens.

Evaluation of nanolipoprotein particles (NLPs) as an in vivo delivery platform

Nanoparticles hold great promise for the delivery of therapeutics, yet limitations remain with regards to the use of these nanosystems for efficient long-lasting targeted delivery of therapeutics, including imparting functionality to the platform, in vivo stability, drug entrapment efficiency and toxicity. To begin to address these limitations, we evaluated the functionality, stability, cytotoxicity, toxicity, immunogenicity and in vivo biodistribution of nanolipoprotein particles (NLPs), which are mimetics of naturally occurring high-density lipoproteins (HDLs). We found that a wide range of molecules could be reliably conjugated to the NLP, including proteins, single-stranded DNA, and small molecules. The NLP was also found to be relatively stable in complex biological fluids and displayed no cytotoxicity in vitro at doses as high as 320 µg/ml. In addition, we observed that in vivo administration of the NLP daily for 14 consecutive days did not induce significant weight loss or result in lesions on excised organs. Furthermore, the NLPs did not display overt immunogenicity with respect to antibody generation. Finally, the biodistribution of the NLP in vivo was found to be highly dependent on the route of administration, where intranasal administration resulted in prolonged retention in the lung tissue. Although only a select number of NLP compositions were evaluated, the findings of this study suggest that the NLP platform holds promise for use as both a targeted and non-targeted in vivo delivery vehicle for a range of therapeutics.

The use of nanolipoprotein particles to enhance the immunostimulatory properties of innate immune agonists against lethal influenza challenge

Recent studies have demonstrated that therapies targeting the innate immune system have the potential to provide transient, non-specific protection from a variety of infectious organisms; however, the potential of enhancing the efficacy of such treatments using nano-scale delivery platforms requires more in depth evaluation. As such, we employed a nanolipoprotein (NLP) platform to enhance the efficacy of innate immune agonists. Here, we demonstrate that the synthetic Toll-like receptor (TLR) agonists monophosphoryl lipid A (MPLA) and CpG oligodeoxynucleotides (CpG) can be readily incorporated into NLPs. Conjugation of MPLA and CpG to NLPs (MPLA:NLP and CpG:NLP, respectively) significantly enhanced their immunostimulatory profiles both in vitro and in vivo compared to administration of agonists alone, as evidenced by significant increases in cytokine production, cell surface expression of activation markers, and upregulation of immunoregulatory genes. Importantly, enhancement of cytokine production by agonist conjugation to NLPs was also observed in primary human dendritic cells. Furthermore, BALB/c mice pretreated with CpG:NLP constructs survived a lethal influenza challenge whereas pretreatment with CpG alone had no effect on survival.

Co-delivery of adjuvant and subunit antigens via a nanoparticle platform induces tissue-associated and systemic adaptive immune responses (P4409)

Vaccination is a critical countermeasure against infection for both biodefense and public health. As many pathogens are encountered at mucosal interfaces, a delivery system that induces robust mucosal immunity is paramount. Here, we investigate a nanolipoprotein particle (NLP) containing the Toll-like receptor 4 agonist monophosphoryl lipid A (MPLA) as a novel vaccine platform using disparate model antigens. Co-administration of MPLA-NLPs with ovalbumin significantly enhances the expansion of OVA-specific T cells in mice in vivo after a single intranasal inoculation, indicating that MPLA-NLPs function as efficient adjuvants. To combine the adjuvant effects with antigen delivery, we engineered MPLA-NLPs to accommodate attachment of His-tagged proteins. Intranasal administration of MPLA-NLPs conjugated to Bacillus anthracis antigens induces specific T cell responses in lung-draining lymph nodes and significant antibody responses in serum and bronchoalveolar lavage. Experiments to assess the immunogenicity of multiple antigens in combination on a single particle and to compare between co-administered formulations are ongoing. These data further support a role for NLPs as a flexible vaccine platform that allows co-delivery of antigen and adjuvant to lung-associated immune tissues and promotes robust adaptive immune responses.

Nanolipoprotein delivery enhances immunostimulatory properties of innate immune agonists and provides protection against lethal influenza challenge (P4218)

Therapies targeting the innate immune system have the potential to provide transient, non-specific protection from a variety of infectious organisms. As such, we have employed a nanolipoprotein (NLP) platform to enhance the efficacy of synthetic innate immune agonists. NLPs are discoidal, nanometer-sized particles comprised of self-assembled phospholipid membranes and apolipoproteins. We demonstrate that the synthetic Toll-like receptor (TLR) ligands monophosphoryl lipid A (MPLA) and CpG oligodeoxynucleotides (CpG ODNs) can be readily incorporated into NLPs. Further, conjugation of both MPLA and CpG ODNs to NLPs significantly enhances their immunostimulatory profiles in vivo compared to administration of agonists alone. Specifically, conjugation to NLPs promotes agonist trafficking to secondary lymphoid organs, enhances and prolongs stimulation of innate immune cells, significantly increases cytokine production, and enhances upregulation of myriad immunoregulatory genes in vivo. Importantly, enhancement of cytokine production by agonists conjugated to NLPs was also observed in primary human dendritic cells. Strikingly, BALB/c mice pretreated with NLP-CpG constructs prior to a lethal influenza challenge were protected from weight-loss induced death, whereas pretreatment with CpG alone had no effect on survival. Taken together, these data suggest that NLP:agonist conjugates potentially represent a novel therapeutic measure against emerging pathogens.

In vitro and in vivo characterization of nanolipoproteins (NLPs) conjugated with innate immune agonists: implications for host-based therapeutics (53.12)

Modulation of the innate immune system has the potential to provide transient, non-specific protection from a variety of infectious organisms. Activation of innate immunity is rapid and short-lived, therefore methods aimed at enhancing and prolonging the response will increase the effectiveness of innate immune targeting as a therapeutic measure. In order to enhance the stimulatory properties of innate immune agonists, we have employed a nanolipoprotein (NLP) platform. NLPs are discoidal, nanometer-sized particles comprised of self-assembled phospholipid membranes and apolipoproteins, analogous to reconstituted HDLs. NLPs have been successfully used in numerous biotechnology applications, including drug delivery and diagnostic imaging. Here, we show that two synthetic TLR ligands: monophosphoryl lipid A (MPLA) and CpG oligodeoxynucleotides (CpG ODNs) can be readily incorporated into NLPs. In addition, the delivery of agonist-conjugated NLPs significantly enhances immunostimulatory effects relative to agonists alone, at low doses, both in vitro and in vivo. Our data demonstrate that conjugation to NLPs promotes agonist trafficking to secondary lymphoid organs, increases cytokine production, and induces upregulation of immunoregulatory genes in peripheral organs. These data suggest that treatment with NLP:agonist conjugates may provide transient protection against lethal pathogen challenge, and experiments to determine their effectiveness at countering infection are ongoing.

Innate immune agonists conjugated to nanolipoproteins elicit robust inflammatory responses in mouse macrophages: implications for host-based therapeutics. (52.10)

Modulation of the innate immune system has the potential to provide transient, non-specific protection from a variety of infectious organisms. We hypothesize that combinatorial formulations of synthetic innate immune agonists may significantly enhance protection over single-agonist formulations. To readily incorporate multiple, chemically diverse agonists onto a single particulate platform for co-localized delivery, nanolipoprotein particles (NLPs) will be used. NLPs are discoidal, nanometer-sized particles comprised of self-assembled phospholipid membranes and apolipoproteins, analogous to reconstituted HDLs. NLPs assembled with human apolipoproteins have been used for numerous biotechnology applications, including membrane protein solubilization, drug delivery, and diagnostic imaging. NLPs can be functionalized to incorporate myriad agonists, including CpG-containing oligonucleotides, monophosphoryl Lipid A, muramyl dipeptide, flagellin, and an LL-37 analog. Development of NLPs incorporating CpGs and MPLA will be described, as well as preliminary results from in vitro analyses, including quantitative inflammatory cytokine secretion, cellular cytotoxicity, and cellular localization. Our data indicate that agonist:NLP constructs are internalized by macrophages, are immunostimulatory, and induce low levels of cellular cytotoxicity.

Kinetic analysis of his-tagged protein binding to nickel-chelating nanolipoprotein particles

Nanolipoprotein particles (NLPs) are discoidal self-assembling membrane mimetics that have been primarily used as a platform for the solubilization and stabilization of membrane proteins. Nickel-chelating nanolipoprotein particles (NiNLPs) containing nickel-chelating lipids (Ni-lipid) for the targeted immobilization of His-tagged proteins hold promise as carriers of hydrophilic biological molecules for a range of applications. The effect of protein loading (i.e., the number of proteins bound per NiNLP) and Ni-lipid content on the time scales and kinetics of binding are important to various applications such as vaccine development, diagnostic imaging, and drug delivery. We have immobilized hexa-His-tagged LsrB, a Yersinia pestis transport protein, onto NiNLPs to examine the effect of protein binding stoichiometry and Ni-lipid content on the time scales and kinetics of protein binding by surface plasmon resonance (SPR). Data indicate that the dissociation half-time increases with Ni-lipid content up to a molar concentration of 35% and decreases as the number of bound protein per NiNLP increases. These findings indicate that the kinetics of protein binding are highly dependent on both the number of bound protein per NiNLP and Ni-lipid content.

Isolation, characterization, and stability of discretely-sized nanolipoprotein particles assembled with apolipophorin-III

BACKGROUND

Nanolipoprotein particles (NLPs) are discoidal, nanometer-sized particles comprised of self-assembled phospholipid membranes and apolipoproteins. NLPs assembled with human apolipoproteins have been used for myriad biotechnology applications, including membrane protein solubilization, drug delivery, and diagnostic imaging. To expand the repertoire of lipoproteins for these applications, insect apolipophorin-III (apoLp-III) was evaluated for the ability to form discretely-sized, homogeneous, and stable NLPs.

METHODOLOGY

Four NLP populations distinct with regards to particle diameters (ranging in size from 10 nm to >25 nm) and lipid-to-apoLp-III ratios were readily isolated to high purity by size exclusion chromatography. Remodeling of the purified NLP species over time at 4 degrees C was monitored by native gel electrophoresis, size exclusion chromatography, and atomic force microscopy. Purified 20 nm NLPs displayed no remodeling and remained stable for over 1 year. Purified NLPs with 10 nm and 15 nm diameters ultimately remodeled into 20 nm NLPs over a period of months. Intra-particle chemical cross-linking of apoLp-III stabilized NLPs of all sizes.

CONCLUSIONS

ApoLp-III-based NLPs can be readily prepared, purified, characterized, and stabilized, suggesting their utility for biotechnological applications.

Hexa-arginine enhanced uptake and residualization of selective high affinity ligands by Raji lymphoma cells

Background

A variety of arginine-rich peptide sequences similar to those found in viral proteins have been conjugated to other molecules to facilitate their transport into the cytoplasm and nucleus of targeted cells. The selective high affinity ligand (SHAL) (DvLPBaPPP)₂LLDo, which was developed to bind only to cells expressing HLA-DR10, has been conjugated to one of these peptide transduction domains, hexa-arginine, to assess the impact of the peptide on SHAL uptake and internalization by Raji cells, a B-cell lymphoma.

Results

An analog of the SHAL (DvLPBaPPP)₂LLDo containing a hexa-arginine peptide was created by adding six D-arginine residues sequentially to a lysine inserted in the SHAL's linker. SHAL binding, internalization and residualization by Raji cells expressing HLA-DR10 were examined using whole cell binding assays and confocal microscopy. Raji cells were observed to bind two fold more ¹¹¹In-labeled hexa-arginine SHAL analog than Raji cells treated with the parent SHAL. Three fold more hexa-arginine SHAL remained associated with the Raji cells after washing, suggesting that the peptide also enhanced residualization of the ¹¹¹In transported into cells. Confocal microscopy showed both SHALs localized in the cytoplasm of Raji cells, whereas a fraction of the hexa-arginine SHAL localized in the nucleus.

Conclusion

The incorporation of a hexa-D-arginine peptide into the linker of the SHAL (DvLPBaPPP)₂LLDo enhanced both the uptake and residualization of the SHAL analog by Raji cells. In contrast to the abundant cell surface binding observed with Lym-1 antibody, the majority of (DvLPBaPPP)₂LArg6AcLLDo and the parent SHAL were internalized. Some of the internalized hexa-arginine SHAL analog was also associated with the nucleus. These results demonstrate that several important SHAL properties, including uptake, internalization, retention and possibly intracellular distribution, can be enhanced or modified by conjugating the SHALs to a short polypeptide.

Quantifying size distributions of nanolipoprotein particles with single-particle analysis and molecular dynamic simulations

Self-assembly of purified apolipoproteins and phospholipids results in the formation of nanometer-sized lipoprotein complexes, referred to as nanolipoprotein particles (NLPs). These bilayer constructs are fully soluble in aqueous environments and hold great promise as a model system to aid in solubilizing membrane proteins. Size variability in the self-assembly process has been recognized for some time, yet limited studies have been conducted to examine this phenomenon. Understanding the source of this heterogeneity may lead to methods to mitigate heterogeneity or to control NLP size, which may be important for tailoring NLPs for specific membrane proteins. Here, we have used atomic force microscopy, ion mobility spectrometry, and transmission electron microscopy to quantify NLP size distributions on the single-particle scale, specifically focusing on assemblies with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and a recombinant apolipoprotein E variant containing the N-terminal 22 kDa fragment (E422k). Four discrete sizes of E422k/DMPC NLPs were identified by all three techniques, with diameters centered at approximately 14.5, 19, 23.5, and 28 nm. Computer simulations suggest that these sizes are related to the structure and number of E422k lipoproteins surrounding the NLPs and particles with an odd number of lipoproteins are consistent with the double-belt model, in which at least one lipoprotein adopts a hairpin structure.

Recombinant expression of the beta-subunit of HLA-DR10 for the selection of novel lymphoma targeting molecules

Selective high-affinity ligands (SHALs) were selected as substitutes for monoclonal antibodies (mAbs) to deliver radioisotopes to malignant tumors. Because a SHAL (5 KD) is considerably smaller in comparison to an antibody (150 KD), a significant therapeutic index (TI) enhancement for radioimmunotherapy (RIT) is anticipated. The antibody-antigen (Ab-Ag) model system chosen for the development of SHALs consists of Lym-1, a MAb with proven selectivity in non-Hodgkin's lymphoma (NHL) patients and its well-characterized Ag, the beta subunit of HLA DR10. Whereas Lym-1 is readily available, the subunit of HLA-DR10 is not. Native, heterodimeric (alpha and beta subunits) HLA-DR10 can be purified from Raji cells, which are known to overexpress this Ag. Inconsistent homogeneity between preparations of HLA-DR10 solubilized in the presence of detergents prompted us to express a recombinant form of the beta subunit of HLA-DR10 in Escherichia coli. Negligible production yields (<or=50 microg/L) were achieved by the expression of the full-length protein in a soluble form. By contrast, yields of 240 mg/L were obtained by expressing only the extracellular domain (ED) of the beta subunit of HLA-DR10 in an insoluble form (inclusion bodies). The recovery yield of refolded protein was 75%. Circular dichroism (CD) and Lym-1 binding studies indicated that the recombinant ED of the beta subunit of HLA-DR10 was properly folded. Therefore, this recombinant protein can be used as a surrogate for native heterodimeric HLA DR10 for the in vitro selection of SHALs and related targeting molecules.

Selective High-Affinity Ligand Antibody Mimics for Cancer Diagnosis and Therapy: Initial Application to Lymphoma/Leukemia

PURPOSE

More than two decades of research and clinical trials have shown radioimmunotherapy to be a promising approach for treating various forms of cancer. Lym-1 antibody, which binds selectively to HLA-DR10 on malignant B-cell lymphocytes, has proved to be effective in delivering radionuclides to non-Hodgkin's lymphoma and leukemia. Using a new approach to create small synthetic molecules that mimic the targeting properties of the Lym-1 antibody, a prototype, selective high-affinity ligand (SHAL), has been developed to bind to a unique region located within the Lym-1 epitope on HLA-DR10.

EXPERIMENTAL DESIGN

Computer docking methods were used to predict two sets of small molecules that bind to neighboring cavities on the beta subunit of HLA-DR10 surrounding a critical amino acid in the epitope, and the ligands were confirmed to bind to the protein by nuclear magnetic resonance spectroscopy. Pairs of these molecules were then chemically linked together to produce a series of bidentate and bisbidentate SHALs.

RESULTS

These SHALs bind with nanomolar to picomolar K(d)'s only to cell lines expressing HLA-DR10. Analyses of biopsy sections obtained from patients also confirmed that SHAL bound to both small and large cell non-Hodgkin's lymphomas mimicking the selectivity of Lym-1.

CONCLUSIONS

These results show that synthetic molecules less than 1/50th the mass of an antibody can be designed to exhibit strong binding to subtle structural features on cell surface proteins similar to those recognized by antibodies. This approach offers great potential for developing small molecule therapeutics that target other types of cancer and disease.

Packaging of single DNA molecules by the yeast mitochondrial protein Abf2p

Mitochondrial and nuclear DNA are packaged by proteins in a very different manner. Although protein-DNA complexes called "nucleoids" have been identified as the genetic units of mitochondrial inheritance in yeast and man, little is known about their physical structure. The yeast mitochondrial protein Abf2p was shown to be sufficient to compact linear dsDNA, without the benefit of supercoiling, using optical and atomic force microscopy single molecule techniques. The packaging of DNA by Abf2p was observed to be very weak as evidenced by a fast Abf2p off-rate (k(off) = 0.014 +/- 0.001 s(-1)) and the extremely small forces (<0.6 pN) stabilizing the condensed protein-DNA complex. Atomic force microscopy images of individual complexes showed the 190-nm structures are loosely packaged relative to nuclear chromatin. This organization may leave mtDNA accessible for transcription and replication, while making it more vulnerable to damage.

Dynamics of protamine 1 binding to single DNA molecules

Protamine molecules bind to and condense DNA in the sperm of most vertebrates, packaging the sperm genome in an inactive state until it can be reactivated following fertilization. By using methods that enable the analysis of protamine binding to individual DNA molecules, we have monitored the kinetics of DNA condensation and decondensation by protamine 1 (P1) and synthetic peptides corresponding to specific segments of the bull P1 DNA binding domain. Our results show that the number of clustered arginine residues present in the DNA binding domain is the most important factor affecting the condensation and stability of the DNA-protamine complex prior to the formation of inter-protamine disulfide cross-links. The high affinity of P1 for DNA is achieved by the coordinated binding of three anchoring domains, which together in bull P1 contain 19 Arg residues. The single DNA molecule experiments show that sequences containing two or more anchoring domains have an off-rate that is at least 3 orders of magnitude slower than those containing a single domain. The use of Arg, rather than Lys residues, and the inclusion of Tyr or Phe residues in the hinge regions between anchoring domains provide additional stability to the complex.

Extracellular domain of myelin oligodendrocyte glycoprotein (MOG) exhibits solvent-dependent conformational transitions

The conformation of the non-glycosylated recombinant form of the extracellar domain of rat MOG (rMOG(1-125)) dissolved in different solvent conditions was studied by CD spectroscopy. The results show that rMOG(1-125) exhibits a predominantly beta sheet conformation in aqueous buffer solution at pH 7.5 and that this 'beta-form' is stabilized by zwitterionic phospholipids, DPC and LPCP. The alpha helical content of the protein can increase from 9% to up to 20% when TFE or anionic detergent LPAP and SDS are added.

Condensation of DNA by spermatid basic nuclear proteins

Two transition proteins, TP1 and TP2, participate in the repackaging of the spermatid genome early in mammalian spermiogenesis, coincident with the first detectable changes in chromatin condensation. Using an optical trap and a two-channel flow cell to move single DNA molecules into buffer containing protein, we have measured the rates of DNA condensation and decondensation induced by the binding of Syrian hamster transition proteins TP1 and TP2 and protamines P1 and P2. The results show that both transition proteins condense free DNA, with rates similar to those of protamine 1 and 2. DNA molecules condensed with TP1 were significantly less stable than DNA condensed by protamine or by TP2. Experiments conducted with a peptide corresponding to the C-terminal 25 residues of TP2 showed that this domain is responsible for condensing DNA. Experiments conducted with two fragments of TP1 containing arginine and lysine residues demonstrated that DNA binding by TP1 must involve more than these basic sequences. Zinc facilitated the condensation of DNA by P2 but not by TP2. The dissociation rates of TP2 and P2 from DNA were not affected by the addition of zinc.

Protamine 1: protamine 2 stoichiometry in the sperm of eutherian mammals

We have compared the relative proportion of protamine 1 (P1) and protamine 2 (P2) bound to DNA in the sperm of a variety of eutherian mammals to obtain insight into how these two proteins interact in sperm chromatin. Gel electrophoresis (combined with microdensitometry) and high performance liquid chromatography (HPLC) were used to determine the content of the two protamines, and the identity of each protein was confirmed by amino-terminal sequencing or amino acid analysis. The sperm of all species examined contained P1, but P2 was found to be present only in certain species. Unlike the fixed ratio of core histones that package DNA into nucleosomes in all somatic cells, the proportion of P2 present in mature sperm was found to be continuously variable from 0 to nearly 80%. These results show that P1 and P2 do not interact with each other or DNA to form a discrete complex or subunit structure that is dependent upon particular P1/P2 stoichiometries. Data obtained from a number of closely and distantly related species also indicate that while the P2 content of sperm chromatin is allowed to vary over a wide range during the course of evolution, the relative proportion of P1 and P2 are tightly regulated within a genus.

Processive translocation and DNA unwinding by individual RecBCD enzyme molecules

RecBCD enzyme is a processive DNA helicase and nuclease that participates in the repair of chromosomal DNA through homologous recombination. We have visualized directly the movement of individual RecBCD enzymes on single molecules of double-stranded DNA (dsDNA). Detection involves the optical trapping of solitary, fluorescently tagged dsDNA molecules that are attached to polystyrene beads, and their visualization by fluorescence microscopy. Both helicase translocation and DNA unwinding are monitored by the displacement of fluorescent dye from the DNA by the enzyme. Here we show that unwinding is both continuous and processive, occurring at a maximum rate of 972 +/- 172 base pairs per second (0.30 microm s(-1)), with as many as 42,300 base pairs of dsDNA unwound by a single RecBCD enzyme molecule. The mean behaviour of the individual RecBCD enzyme molecules corresponds to that observed in bulk solution.

Characteristics of human sperm chromatin structure following an episode of influenza and high fever: a case study

Semen samples from a fertile patient presenting with influenza and a 1-day fever of 39.9 degrees C were obtained and analyzed at 18-66 days postfever (dpf) for sperm nuclear proteins, DNA stainability, free thiols (-SH), and susceptibility to DNA denaturation in situ. At 18 dpf, 36% of sperm demonstrated denatured DNA as measured by the sperm chromatin structure assay (SCSA), and decreased to 23% by 39 dpf. Samples at 33 and 39 dpf contained 49% and 30%, respectively, of cells with increased DNA stainability (HIGRN). A unique sperm nuclear protein band migrating between histones and protamines on acid-urea gels appeared at 33 and 39 dpf and nearly disappeared by 52 dpf. Amino acid sequencing of the first 8 N-terminal residues identified this protein as the precursor to protamine 2. The protamine P1 and P2 ratio remained normal, whereas the histone to protamine ratio increased slightly at 33 to 39 dpf. Flow cytometric measurements of nuclear -SH groups revealed the greatest reduction in free nuclear thiols at 33 dpf, and returned to normal by 45 dpf. The time of appearance of the unprocessed protamine 2 precursor and the relative increase in histone suggest a fever-related disruption of the synthesis of mRNA that codes for a P2 processing enzyme or enzymes. Increased DNA staining is likely due to the increased histone/protamine ratio. This case study demonstrates that fever/influenza can have latent effects on sperm chromatin structure and may result in transient release of abnormal sperm.

DNA condensation by protamine and arginine-rich peptides: analysis of toroid stability using single DNA molecules

Both somatic cells and sperm have been shown to take up exogenous DNA, but the frequency of its integration is usually low. Scanning probe microscopy studies of sperm chromatin and synthetic DNA-protamine complexes indicate that the coiling of DNA into toroidal subunits, a process initiated in the maturing spermatid to prepare its genome for delivery into the egg, can be mimicked by simply adding protamine to DNA in vitro. The increased resistance of DNA-protamine complexes to nuclease digestion and their structural similarity to native sperm chromatin suggest that the packaging of DNA by protamine might offer a new approach for improving the efficiency of DNA uptake by sperm. Decondensation experiments performed with individual DNA molecules have provided a direct measure of the stability of toroids produced using salmon protamine and smaller arginine-rich peptides. These experiments show that the arginine content of protamine-related sequences can have a dramatic effect on their rate of dissociation from DNA. This technique and the information it provides can be used to identify protamine analogs that can be bound to DNA to increase the efficiency of its uptake by sperm and other cells.

Analysis of hamster protamines: primary sequence and species distribution

Basic nuclear proteins were isolated from the sperm of the Syrian hamster Mesocricetus auratus and characterized by gel electrophoresis, amino acid analysis, and sequencing. Analyses of the proteins by gel electrophoresis show that sperm of this species contain both protamines 1 and 2. The two proteins were purified by HPLC and the complete primary sequence of hamster protamine 1 was determined by automated amino acid sequence analysis. The protein sequence was subsequently confirmed by sequencing the PCR-amplified protamine 1 gene. The first forty-two residues of the hamster protamine 2 sequence were obtained by amino acid sequence analysis of the isolated protein, and this sequence was also confirmed and extended by sequencing the gene. Total basic nuclear protein was also isolated from sperm of six other species of hamsters, the protamines were identified by HPLC and amino acid analysis, and the proportion of protamines 1 and 2 in each species was determined. Marked differences in the protamine 2 content of sperm were observed among the different species of hamster. This variation and the high level of sequence similarity between mouse and hamster protamines provide insight into how the two protamines may be organized in sperm chromatin. Mol. Reprod. Dev. 54:273-282, 1999. Published 1999 Wiley-Liss, Inc.

Protamine-induced condensation and decondensation of the same DNA molecule

The DNA in sperm and certain viruses is condensed by arginine-rich proteins into toroidal subunits, a form of packaging that inactivates their entire genome. Individual DNA molecules were manipulated with an optical trap to examine the kinetics of torus formation induced by the binding of protamine and a subset of its DNA binding domain, Arg6. Condensation and decondensation experiments with lambda-phage DNA show that toroid formation and stability are influenced by the number of arginine-rich anchoring domains in protamine. The results explain why protamines contain so much arginine and suggest that these proteins must be actively removed from sperm chromatin after fertilization.

Detection of P2 precursors in the sperm cells of infertile patients who have reduced protamine P2 levels

OBJECTIVE

To determine whether the reduction in the protamine P2 content (increased P1/P2 ratio) reported in some infertile patients could result from incomplete processing of protamine P2 precursors.

DESIGN

Analysis of samples with a marked reduction in the protamine P2 content using polyacrylamide gel electrophoresis and subsequent detection of protamine P2 precursors through Western blot analysis.

SETTING

University departments and laboratories.

PATIENT(S)

One hundred eighty-four men undergoing an evaluation for infertility.

MAIN OUTCOME MEASURE(S)

Comparative Western blot analysis of nuclear sperm proteins using specific antibodies to protamine P1 and protamine P2.

RESULT(S)

After selection of the samples with a marked reduction of the protamine P2 content and subsequent analysis by Western blot, a small proportion of putative P2 precursors was detected in most samples, whereas a significant increase was detected in two of them.

CONCLUSION(S)

In some infertile men, a reduction in the protamine P2 content relative to protamine P1 (increased P1/P2 ratio) is detected concomitant with an increase in the amount of putative P2 precursors. This could represent the first report of incomplete processing of a nuclear sperm protein in humans.

X-ray laser microscopy of rat sperm nuclei

The development of high brightness and short pulse width (< 200 picoseconds) x-ray lasers now offers biologists the possibility of high-resolution imaging of specimens in an aqueous environment without the blurring effects associated with natural motions and chemical erosion. As a step toward developing the capabilities of this type of x-ray microscopy, a tantalum x-ray laser at 44.83 angstrom wavelength was used together with an x-ray zone plate lens to image both unlabeled and selectively gold-labeled dried rat sperm nuclei. The observed images show approximately 500 angstrom features, illustrate the importance of x-ray microscopy in determining chemical composition, and provide information about the uniformity of sperm chromatin organization and the extent of sperm chromatin hydration.

Formation of intraprotamine disulfides in vitro

When mammalian protamine is dissolved in aqueous buffers at neutral or alkaline pH, both ends of the protein fold inward toward the center of the molecule and form disulfide crosslinks that stabilize several different structures. In the absence of reducing agents, these folded forms of protamine may be visualized and quantitated by gel electrophoresis. Using this technique, we have examined the formation of bull protamine disulfides in solution and describe a variety of factors that affect this process. At pH 8, disulfide-stabilized folded forms of protamine appear within minutes after solubilization of the fully reduced protein. Five different monomers are detected by electrophoresis. Each of these monomers is stabilized by at least one disulfide crosslink and migrates with a distinct mobility, ahead of the fully reduced and extended protein. Under certain conditions, dimers of these folded structures crosslinked by interprotamine disulfides are also formed. The appearance of these disulfide-crosslinked forms of protamine is effected by air oxidation, accelerated at alkaline pH, inhibited upon lowering the pH below pH 7 and eliminated by modifying the protein's cysteine residues. Similar intramolecular disulfides are also produced after the protamine molecule binds to DNA. These results suggest that only those cysteines located within the amino- and carboxyterminal ends of the protein appear to participate in forming intramolecular disulfides in vitro.

Identification of bull protamine disulfides

We have identified the disulfide cross-links in bull protamine by titrating intact bull sperm with dithiothreitol (DTT) and following the modification of each cysteine residue with tritiated iodoacetate. The derivatization of each cysteine was monitored by a combination of HPLC, peptide mapping, and protein sequencing. Analyses of total free sulfhydryls show that all seven of the bull protamine cysteines are cross-linked as disulfides in mature sperm. The first disulfide is reduced at a DTT:protamine cysteine (DTT:Cys) ratio of 0.3 and the last at a ratio of 2.0. Intra- and intermolecular disulfides were identified by correlating the reduction of specific disulfides with the dissociation of protamine from DNA in partially reduced sperm and sperm treated with N,N'-ethylenedimaleimide, a bifunctional disulfide cross-linking agent. Three intermolecular and two intramolecular disulfides were identified. The results of these experiments demonstrate that the amino- and carboxy-terminal ends of the bull protamine molecule are folded inward toward the center of the molecule and are locked in place, each by a single intramolecular disulfide bridge. Three intermolecular disulfides cross-link neighboring protamine molecules around the DNA helix in such a manner that the protamines cannot be dissociated from DNA without first reducing the interprotamine disulfides.

Reactivity and adduct formation of a polyaromatic hydrocarbon, 7-bromomethylbenz[a]anthracene, with chromatin histone proteins

The alkylation of histones by the direct-acting carcinogen 7-bromomethylbenz[a]anthracene was demonstrated both in vivo and in vitro. The relative molar reactivity for mouse liver histones in vivo was H3 greater than H1 greater than H2b greater than H4 greater than H2a. The in vitro modification of histone H3 was examined in detail. Amino acid adducts stable to acid hydrolysis were separated after acetylation by reversed-phase high-performance liquid chromatography and characterized using ultraviolet absorbance spectra and synthetic amino acid adduct standards. Three major adducts were observed and tentatively identified as cysteinyl, lysyl and histidinyl adducts of histone H3.

Mouse protamine 2 is synthesized as a precursor whereas mouse protamine 1 is not

The nuclei of mouse spermatozoa contain two protamine variants, mouse protamine 1 (mP1) and mouse protamine 2 (mP2). The amino acid sequence predicted from mP1 cDNAs demonstrates that mP1 is a 50-amino-acid protein with strong homology to other mammalian P1 protamines. Nucleotide sequence analysis of independently isolated, overlapping cDNA clones indicated that mP2 is initially synthesized as a precursor protein which is subsequently processed into the spermatozoan form of mP2. The existence of the mP2 precursor was confirmed by amino acid composition and sequence analysis of the largest of a set of four basic proteins isolated from late-step spermatids whose synthesis is coincident with that of mP1. The sequence of the first 10 amino acids of this protein, mP2 precursor 1, exactly matches that predicted from the nucleotide sequence of cDNA and genomic mP2 clones. The amino acid composition of isolated mP2 precursor 1 very closely matches that predicted from the mP2 cDNA nucleotide sequence. Sequence analysis of the amino terminus of isolated mature mP2 identified the final processing point within the mP2 precursor. These studies demonstrated that mP2 is synthesized as a precursor containing 106 amino acids which is processed into the mature, 63-amino-acid form found in spermatozoa.

High-performance liquid chromatographic separation and partial characterization of human protamines 1, 2, and 3

A method for separating the three human protamines by HPLC of underivatized, total protamine extracts on a Nucleosil RP-C18 column is described. The identities of the three proteins have been confirmed by a combination of disc gel electrophoresis, amino acid composition, and primary sequence analysis. The results show that human protamine 3 elutes first, closely followed by protamine 2. Protamine 1 elutes later. The amino acid compositions and partial amino terminal sequences of human protamines 2 and 3 indicate that these two proteins are very closely related and suggest that they differ only by three amino-terminal amino acids.

A corrected primary sequence for bull protamine

We have redetermined the primary sequence for bull protamine using HPLC peptide mapping and automated amino-acid sequencing techniques and report, on the basis of these findings, that the previously published amino-acid sequence for this protein is incorrect. The correct protamine sequence is 50 amino acids in length and differs from the original published sequence by the tripeptide -Cys-39-Arg-40-Arg-41-. Analyses of protamine tryptic peptides derived from nine diverse breeds of Bos tarus and Bos indicus indicate that this sequence is present in the protamine of each breed and that it does not represent a variant or mutation.