Synthetic peptides derived from the sequence of human C-reactive protein inhibit the enzymatic activities of human leukocyte elastase and human leukocyte cathepsin G

The autodisplay story, from discovery to biotechnical and biomedical applications

Among the pathways used by gram-negative bacteria for protein secretion, the autotransporter pathway represents a solution of impressive simplicity. Proteins are transported, independent of their nature as recombinant or native passengers, as long as the coding nucleotide sequence is inserted in frame between those of an N-terminal signal peptide and a C-terminal domain, referred to as the beta-barrel of the outer membrane translocation unit. The immunoglobulin A1 (IgA1) protease from Neisseria gonorrhoeae was the first identified member of the autotransporter family of secreted proteins. The IgA1 protease was employed in initial experiments investigating autotransporter-mediated surface display of recombinant proteins and to investigate structural and functional requirements. Various other autotransporter proteins have since been described, and the autodisplay system was developed on the basis of the natural Escherichia coli autotransporter protein AIDA-I (adhesin involved in diffuse adherence). Autodisplay has been used for the surface display of random peptide libraries to successfully screen for novel enzyme inhibitors. The autodisplay system was also used for the surface display of functional enzymes, including esterases, oxidoreductases, and electron transfer proteins. Whole E. coli cells displaying enzymes have been utilized to efficiently synthesize industrially important rare organic compounds with specific chirality. Autodisplay of epitopes on the surface of attenuated Salmonella carriers has also provided a novel way to induce immune protection after oral vaccination. This review summarizes the structural and functional features of the autodisplay system, illustrating its discovery and most recent applications. Autodisplay facilitates the export of more than 100,000 recombinant molecules per single cell and permits the oligomerization of subunits on the cell surface as well as the incorporation of inorganic prosthetic groups after transport of apoproteins onto the bacterial surface without disturbing bacterial integrity or viability. We discuss future biotechnical and biomedical applications in the light of these achievements.

Autodisplay: efficient bacterial surface display of recombinant proteins

To display a protein or peptide with a distinct function at the surface of a living bacterial cell is a challenging exercise with constantly increasing impact in many areas of biochemistry and biotechnology. Among other systems in Gram-negative bacteria, the Autodisplay system provides striking advantages when used to express a recombinant protein at the surface of Escherichia coli or related bacteria. The Autodisplay system has been developed on the basis of and by exploiting the natural secretion mechanism of the AIDA-I autotransporter protein. It offers the expression of more than 10(5) recombinant molecules per single cell, permits the multimerization of subunits expressed from monomeric genes at the cell surface, and allows, after transport of an apoprotein to the cell surface, the incorporation of an inorganic prosthetic group without disturbing cell integrity or cell viability. Moreover, whole cells displaying recombinant proteins by Autodisplay can be subjected to high-throughput screening (HTS) methods such as ELISA or FACS, thus enabling the screening of surface display libraries and providing access to directed evolution of the recombinant protein displayed at the cell surface. In this review, the application of the Autodisplay system for the surface display of enzymes, enzyme inhibitors, epitopes, antigens, protein and peptide libraries is summarised and the perspectives of the system are discussed.

IL-2 Induces T Cell Adherence to Extracellular Matrix: Inhibition of Adherence and Migration by IL-2 Peptides Generated by Leukocyte Elastase

Migration of inflammatory cells requires cell adhesion and their subsequent detachment from the extracellular matrix (ECM). Leukocyte activation and migration must be terminated to stop inflammation. Here, we report that IL-2 enhances human T cell adherence to laminin, collagen type IV, and fibronectin (FN). In contrast, neutrophil elastase, an enzyme activated during inflammation, degrades IL-2 to yield IL-2 fractions that inhibit IL-2-induced T cell adhesion to FN. The amino acid composition of two of these IL-2 fractions, which appear to block T cell adherence to FN, were analyzed, and three peptides were consequently synthesized. The three peptides IVL, RMLT, and EFLNRWIT, but not the corresponding inversely synthesized peptides, inhibited T cell adhesion to FN induced by a variety of activators: IL-2, IL-7, macrophage inflammatory protein (MIP)-1β, and PMA, as well as anti-CD3 and anti-β1 integrin-activating mAb. Moreover, these IL-2 peptides inhibited T cell chemotaxis via FN-coated membranes induced by IL-2 and MIP-1β. Inhibition of T cell adherence and migration apparently involves abrogation of the rearrangement of the T cell actin cytoskeleton. Thus, the migrating immune cells, the cytokines, and the ECM can create a functional relationship in which both inflammation-inducing signals and inhibitory molecules of immune responses can coexist; the enzymatic products of IL-2 may serve as natural feedback inhibitors of inflammation.

Peptides derived from human C-reactive protein inhibit the enzymatic activities of human leukocyte elastase and cathepsin G: use of overlapping peptide sequences to identify a unique inhibitor

Ten overlapping 15-mer peptides, spanning the entire inner disulfide loop of human C-reactive protein (residues 36-97), were used to isolate a potent inhibitor of the enzymes human leukocyte elastase and human leukocyte cathepsin G, which are associated with chronic inflammatory tissue damage. In contrast to the inability of intact C-reactive protein to inhibit both enzymes, the synthetic peptide E62ILIFWSKDIGYSFT76 inhibited leukocyte elastase (Ki = 0.18 microM) and cathepsin G (Ki = 0.25 microM) at concentrations far lower than the acute-phase concentration of C-reactive protein. Several peptide-enzyme binding motifs were elucidated by structure-function studies, with the Glu62 residue being crucial in establishing long-range subsite interactions. Peptides derived from C-reactive protein, which may be generated in vivo by neutrophil-mediated proteolysis as part of a complex regulatory homeostatic mechanism, may play an important role in regulating the activity of matrix-degrading enzymes, specifically at sites of inflammation. The present results thus may shed additional insight on the physiological functions of the major acute-phase reactant C-reactive protein, and perhaps be used as a basis for the design of novel therapeutic substances.