Persistency of Adenoviral-Mediated Lysostaphin Expression in Goat Mammary Glands

Lysostaphin: Engineering and Potentiation toward Better Applications

Lysostaphin is a potent bacteriolytic enzyme with endopeptidase activity against the common pathogen Staphylococcus aureus. By digesting the pentaglycine crossbridge in the cell wall peptidoglycan of S. aureus including the methicillin-resistant strains, lysostaphin initiates rapid lysis of planktonic and sessile cells (biofilms) and has great potential for use in agriculture, food industries, and pharmaceutical industries. In the past few decades, there have been tremendous efforts in potentiating lysostaphin for better applications in these fields, including engineering of the enzyme for higher potency and lower immunogenicity with longer-lasting effects, formulation and immobilization of the enzyme for higher stability and better durability, and recombinant expression for low-cost industrial production and in situ biocontrol. These achievements are extensively reviewed in this article focusing on applications in disease control, food preservation, surface decontamination, and pathogen detection. In addition, some basic properties of lysostaphin that have been controversial and only elucidated recently are summarized, including the substrate-binding properties, the number of zinc-binding sites, the substrate range, and the cleavage site in the pentaglycine crossbridge. Resistance to lysostaphin is also highlighted with a focus on various mechanisms. This article is concluded with a discussion on the limitations and future perspectives for the actual applications of lysostaphin.

Adeno-associated-virus-mediated transduction of the mammary gland enables sustained production of recombinant proteins in milk

Biopharming for the production of recombinant pharmaceutical proteins in the mammary gland of transgenic animals is an attractive but laborious alternative compared to mammalian cell fermentation. The disadvantage of the lengthy process of genetically modifying an entire animal could be circumvented with somatic transduction of only the mammary epithelium with recombinant, replication-defective viruses. While other viral vectors offer very limited scope for this approach, vectors based on adeno-associated virus (AAV) appear to be ideal candidates because AAV is helper-dependent, does not induce a strong immune response and has no association with disease. Here, we sought to test the suitability of recombinant AAV (rAAV) for biopharming. Using reporter genes, we showed that injected rAAV efficiently transduced mouse mammary cells. When rAAV encoding human myelin basic protein (hMBP) was injected into the mammary glands of mice and rabbits, this resulted in the expression of readily detectable protein levels of up to 0.5 g/L in the milk. Furthermore we demonstrated that production of hMBP persisted over extended periods and that protein expression could be renewed in a subsequent lactation by re-injection of rAAV into a previously injected mouse gland.

Crystal structure of the antimicrobial peptidase lysostaphin from Staphylococcus simulans

Staphylococcus simulans biovar staphylolyticus lysostaphin efficiently cleaves Staphylococcus aureus cell walls. The protein is in late clinical trials as a topical anti-staphylococcal agent, and can be used to prevent staphylococcal growth on artificial surfaces. Moreover, the gene has been both stably engineered into and virally delivered to mice or livestock to obtain resistance against staphylococci. Here, we report the first crystal structure of mature lysostaphin and two structures of its isolated catalytic domain at 3.5, 1.78 and 1.26 Å resolution, respectively. The structure of the mature active enzyme confirms its expected organization into catalytic and cell-wall-targeting domains. It also indicates that the domains are mobile with respect to each other because of the presence of a highly flexible peptide linker. The high-resolution structures of the catalytic domain provide details of Zn²⁺ coordination and may serve as a starting point for the engineering of lysostaphin variants with improved biotechnological characteristics.

Silk-elastinlike protein polymer hydrogels for localized adenoviral gene therapy of head and neck tumors

Vector dissemination, transient gene expression, and rapid clearance are major obstacles to successful human gene therapy. In this study, we investigated the effect of silk-elastinlike protein polymer (SELP) hydrogels on biodistribution and anticancer efficacy of adenoviral gene therapy in a head and neck cancer model. Transcriptional activities of adenovirus carrying beta-galactosidase (Ad-LacZ) and luciferase (Ad-Luc) reporter genes were evaluated in (nu/nu) mice with head and neck cancer as a function of polymer concentration. Antitumor efficacy of thymidine kinase encoding adenovirus (Ad-Tk) and ganciclovir (GSV) combination was also evaluated. SELP (4 wt %) matrices localized viral release, minimized dissemination to liver, and enhanced reporter gene expression levels by 4-8-fold compared to virus alone. SELP- Ad-Tk with GSV reduced tumor volume significantly compared to the virus alone. SELPs provide a means for temporal and spatial control of viral gene delivery to head and neck tumors.

Mammary gland expression of antibacterial peptide genes to inhibit bacterial pathogens causing mastitis

As a step toward prevention of bovine mastitis, a plasmid-mediated gene transfer technique was used to enable mammary cells to synthesize and secrete bovine lactoferricin and bovine tracheal antibacterial peptides. For this purpose, a series of mammary tissue-specific expression vectors, harboring the antibacterial peptide gene, the 5'-flanking regulation sequence of goat beta-casein, and the bovine growth hormone polyadenylation signal sequence, were constructed using a eukaryotic expression vector pIRES1-neo. The mammary gland tissue-specific expression vector carrying the antimicrobial peptide genes dissolved in physiologic saline was injected directly into the lactating mammary glands of goats. The milk samples after injection were checked by Tricine-SDS-PAGE and bacterium inhibition zone assay. The results of these tests showed that the mammary gland tissue-specific expression vector driven by the goat beta-casein gene promoter could efficiently direct the expression of antibacterial peptides in goat milk; the expression of antibacterial proteins lasted for 3 to 6 d. All of the milk samples collected from the mammary glands that had been injected with different vectors harboring the antibacterial peptide gene(s) exhibited bacteriostatic activity against different bacterial pathogens. These results demonstrated that the mammary gland tissue-specific expression vector could be used to introduce antibacterial peptide gene into the goat mammary gland, enabling secretion of a bioactive form of antibacterial peptide in the milk. This successful expression of antibacterial peptides in goat mammary glands provided a possible method to prevent mastitis in ruminants.

High-level expression of recombinant human nerve growth factor beta in milk of nontransgenic rabbits

The technology for the large-scale production of therapeutic recombinant proteins remains a challenge in the biopharmaceutical industry. In this study, we reported a nontransgenic approach to producing a large quantity of human nerve growth factor beta (hNGF-beta) in rabbit milk by employing a recombinant adenoviral expression system. After directly instilling hNGF-beta recombinant adenoviruses into rabbit mammary glands, a polypeptide with a molecular weight of 13.2 kDa was detected in rabbit milk. The maximal expression level of hNGF-beta reached 346 mug/ml. The biological activity of recombinant hNGF-beta was confirmed using PC12 cells and cultures of dorsal root ganglion neurons from chicken embryos. Our data suggest that instilling recombinant adenovirus directly into the mammary gland of mammals is an efficient approach to producing a large quantity of hNGF-beta.

High-level expression of human lactoferrin in the milk of goats by using replication-defective adenoviral vectors

The expression of human lactoferrin in the mammary gland is an attractive approach to diminish its current production cost. Previous attempts to produce lactorferrin in the milk of transgenic animals resulted in very high cost and uncertain results. In this paper, we have directly infused replication-defective adenovirus encoding human lactoferrin cDNA into the mammary gland of goats via the teat canal. In this way, we obtained a high level of expressed human lactoferrin up to 2g/L in the milk of goats. The milk serum was collected from the infected mammary gland 48 h post-infection and subjected to a 10% SDS-PAGE and Western blotting. A approximately 80-kDa protein was visualized after viral vector infection. Our results demonstrate that intraductal injection of recombinant replication-defective adenovirus vectors may provide a very useful tool for large-scale production of recombinant proteins of biopharmaceutical interest.