A biofilm is a community of bacteria attached to a surface that exhibit high resistance to antibiotics and human immunity. Biofilm formation poses a serious threat to the medical and shipping industries in the following ways:

1. Medical Industry
   • Protein adsorption, cell-adhesion, and subsequent biofilm formation have been found to lead to failure of medical implants and infection in patients.¹
2. Shipping Industry
   • Government and industry spend upwards of $5.7 billion annually in the control of marine biofouling. High levels of biofouling result in increased drag and the subsequent loss of hydrodynamic performance.²
     

   
   
   Figure X. (A) Biofilm formation leads to failure of implanted cardiac devices and heart valve infection. (B) Biofilm formation on the hulls of ships leads to loss of optimal hydrodynamic performance and structural failures.

To address this issue, we aimed to develop an anti-microbial adhesive peptide composed of two components. We envision these domains can be modulated to suit a variety of functional adhesive applications:

1. Component 1: Adhesive Domain
   • Because biofilm formation affects both organic and inorganic substrates, the anti-biofilm coating should show strong adhesion to a variety of surfaces. Mussel adhesive proteins (MAPs), which are secreted by the mussel to help it anchor and survive in the harsh conditions of the intertidal zone, would be ideal for this application. MAP adhesion has been well-characterized and has been investigated in biomimetic adhesive applications in the past. We intend to broaden the scope of their application by looking at their inclusion in the first anti-biofilm adhesive recombinant protein.³
2. Component 2: Anti-Microbial Domain
   • As our anti-microbial domain, we selected LL-37, a member of the cathelicidin family of peptides, due to the potency of its lipid bilayer disruption by toroidal pore formation. Because this peptide is toxic to the E. coli in which we intend to produce it, we designed a controlled, inducible system that limits basal expression. A novel T7 riboregulation system that controls expression at both the transcriptional and translational levels was designed. This improved system is a precise synthetic switch for the expression of cytotoxic substances.^4,5
3. Environmental Concerns
   • Concerns of environmental toxicity often arise in materials being investigated for anti-fouling activity such as copper paints and Muntz metal. Therefore, we set out to develop an anti-fouling coating with strong adhesive activity to limit leachants into the environment. Additionally, the selection of a MAP, found in a biological organism, as our adhesive domain is crucial to maintaining the soundness of our product's eco-friendliness.

1. Control expression of anti-microbial peptides:
   • Since we intend to synthesize an anti-microbial peptide, it is possible that the peptide will be toxic to the E. coli used in our synthetic route. To improve our overall protein yield, we designed a plasmid with specific locks in place to control expression of the T7 RNA polymerase, an RNA polymerase from the T7 bacteriophage. When the T7 RNA polymerase is expressed, it can then specifically target the T7 Promoter located in a different plasmid upstream of our coding sequence, initiating protein translation. The specific mechanism of our T7 riboregulation system is outlined in a section below.^6,7
2. Modular construct design:
   • As our adhesive domain, we selected the mussel foot protein (mefp) consensus sequence mefp 1-mgfp 5-mefp-1, which was found to be effective in Lee et al., 2008. At the N-terminus, we included a the twin Strep-FLAG tag, used in the purification and isolation of our construct and that can be readily cleaved. The LL-37 antimicrobial peptide, which is short enough to be inserted via primer overhang, is linked via a 36 residue linker, which we believe is long enough not to engender any unforeseen structural interaction between our domains. On the other side of the foot protein, we included an sfGFP connected by a shorter linker, which will be used to assay presence and yield of construct. Using targeted primers, the construct can be amplified in its entirety, or only with the anti-microbial or GFP segment. Note that the entire construct was designed so that a variety of functional peptide domains can be substituted for LL-37 if desired. A diagram of our entire construct is presented below:
   
   
   Figure X. A diagram illustrating the components in our final construct. The black domain is our anti-microbial peptide, LL-37, while the blue domain represents the recombinant mussel foot protein adhesive component. All other components are labeled accordingly and restriction sites are highlighted to emphasize the modularity of each separate region.
   

3. Characterize peptide's adhesion and anti-microbial properties:
   • A number of tests were run to assay peptide adhesion

1. An Improved T7 System Expression System

   Our first challenge in making Ampersand was to develop a system that limits basal expression of our peptide, due to its toxicity to the host. Several expression systems have been designed in the past, including the T7 promoter and T7 RNA Polymerase system, to suppress protein expression. The current BL21 (DE3) strain is leaky due to the weak suppressing promoter lacUV5 that drives T7 RNA polymerase in the DE3 strains. As a result, low levels of toxic protein are constitutively expressed, ultimately killing the host it was made in and in turn lowering the overall yield of the protein produced.

   In order to reduce the expression of T7 RNA polymerase and create an efficient system for the expression of recombinant proteins in E. coli we chose to introduce two levels of regulation:

   • Transcriptional Regulation: We will use pZE21 of the pZ system of vectors developed by Lutz and Buschard with the P_LlacO promoter to inhibit the expression of T7 RNA polymerase.
   • Translational Regulation: We will use the artificial riboregulatory elements devised by Isaacs et al. to restrict translation of the mRNA sequence encoding T7 RNA Polymerase.⁹ The cis-repressing RNA (crRNA) sequence will be inserted downstream of the promoter driving T7 RNA Polymerase and upstream of the ribosomal binding site (RBS). The crRNA is complimentary to the RBS and forms a stem loop at the 5’ end of the mRNA segment, blocking ribosomal docking and translation. A second promoter, P_LtetO will express the trans-activating RNA (taRNA) capable of undergoing a linear-loop interaction that will expose the RBS and allow for translation of T7 RNA Polymerase. The ribo-regulated T7 RNA Polymerase will be ultimately incorporated into the genome of strain capable of high protein production. A second pZ plasmid will contain the gene of interest expressed by a T7 promoter.

   In summary, the benefits to this type of system are its robustness, portability, and efficiency in that it does not require the cell to expend more energy on the constitutive synthesis of another protein. We theorize that by utilizing these two levels of control we will be able to reduce the expression of T7 RNA polymerase and produce a system with zero basal expression of the gene of interest and permit stable cloning of toxic recombinant proteins.

   
   Figure X. This diagram illustrates the T7 riboregulation system developed to ensure low basal levels of protein expression.⁹

2. Why Mussel Adhesion Proteins?

   The ability for mussels to survive the harsh conditions of the intertidal zone is directly related to their capability to bind to both organic and inorganic surfaces that they come in contact with. As a result, these mussels have evolved to secrete “adhesion proteins” that enable formation of powerful bonds in an otherwise deleterious aqueous environment. The quantity known as “work of adhesion (W_A)” amongst interfaces in an aqueous environment is significantly less favorable due to the water-surface interactions that must be outcompeted by the adhesive if binding is to occur.¹⁰ Therefore, these mussel adhesion proteins offer a promising avenue towards enhanced bioadhesives that retain functionality in aqueous environments.

   The structure responsible for the binding of mussels to these surfaces is known as the byssus, which is composed of a well-characterized assembly of approximately 25-30 proteins.¹⁰ The byssus manifests itself as an outgrowth from the mussel’s “foot” composed of threads, which terminate in plaques deposited on the surface. Thus far, a total of 5 proteins, known as mussel foot proteins (mfp’s), were shown to be unique to the plaque. Of these 5 plaque proteins, mfp-3 and mfp-5 have elicited the most investigation for adhesive applications, as both are localized at the interface between the plaque and surface. Additionally, it was shown that all such mfp’s have a uniquely high concentration of tyrosine, which is post-translationally modified to 3,4-dihydroxy-L-phenylalanine (L-Dopa). Atomic force microscopy studies focusing on a single dopa residue showed that its interaction with a metal oxide surface involves a remarkably high strength, reversible coordination bond.¹¹ It has been shown that catechol oxidase enzymes present in mfp secretions are able to convert the catechol groups of L-dopa into reactive orthoquinone functionalities, which undergo irreversible covalent bonding with organic surfaces.^11,12 Ultimately, the high degree of surface affinity such dopa-containing peptides possess makes them novel tools in the development of biomimetic adhesive peptides.

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