Jordi X. Feliu

Optimized release of recombinant proteins by ultrasonication of E. coli cells

The release kinetics of beta-galactosidase protein have been determined during small-scale ultrasonication of E. coli cells. Among several studied parameters, ionic strength and cell concentration have the least influence on the rate of protein recovery, whereas sample volume and acoustic power dramatically affect the final yield of soluble protein in the cell-free fraction. The analysis of these critical parameters has prompted us to propose a simple model for E. coli disintegration that only involves acoustic power and sample volume, and which allows prediction of optimal sonication times to recover significant amounts of both natural and recombinant proteins in a given set of relevant conditions.

Engineering of solvent-exposed loops in Escherichia coli β-galactosidase

The Escherichia coli β‐galactosidase is a high molecular mass tetrameric enzyme extensively used as a molecular marker. Despite its proven utility as a partner in fusion proteins, previous attempts to generate insertional mutants rendered inactive or poorly active enzymes, hampering its further engineering for the construction of multifunctional enzymes. We have explored several solvent‐exposed loops on the tetramer, namely those spanning residues 246–254, 271–287, 578–584, 770–773, and 793–806, as acceptor sites to accommodate functional protein segments on the surface of active β‐galactosidase enzymes. An RGD‐containing antigenic peptide positioned in these sites interacts efficiently with specific monoclonal antibodies as well as target integrins on the surface of mammalian cells. The resulting chimeric enzymes are soluble, stable, produced in high yields and enzymatically active. Moreover, the identified insertion sites could be appropriated for the design of promising β‐galactosidase‐based molecular sensors.

Exploiting viral cell-targeting abilities in a single polypeptide, non-infectious, recombinant vehicle for integrin-mediated DNA delivery and gene expression.

A recombinant, multifunctional protein has been designed for optimized, cell-targeted DNA delivery and gene expression in mammalian cells. This hybrid construct comprises a viral peptide ligand for integrin alpha(V)beta(3) binding, a DNA-condensing poly-L-lysine domain, and a complete, functional beta-galactosidase protein that serves simultaneously as purification tag and DNA-shielding agent. This recombinant protein is stable; it has been produced successfully in Escherichia coli and can be purified in a single step by affinity chromatography. At optimal molar ratios, mixtures of this vector and a luciferase-reporter plasmid form stable complexes that transfect cultured cells. After exposure to these cell-targeted complexes, steady levels of gene expression are observed for more than 3 days after transfection, representing between 20 and 40% of those achieved with untargeted, lipid-based DNA-condensing agents. The principle to include viral motifs for cell infection in single polypeptide recombinant proteins represents a promising approach towards the design of non-viral modular DNA transfer vectors that conserve the cell-target- ing specificity of native viruses and that do not need further processing after bioproduction in a recombinant host.

Distinct mechanisms of antibody-mediated enzymatic reactivation in β-galactosidase molecular sensors

The antibody‐mediated reactivation of engineered Escherichia coli β‐galactosidases [Benito et al. (1996) J. Biol. Chem. 271, 21251–21256] has been thoughtfully investigated in three recombinant molecular sensors. Proteins M278VP1, JX772A and JX795A display the highly antigenic G‐H loop peptide segment of foot‐and‐mouth disease virus VP1 protein, accommodated in different solvent‐exposed loops of the assembled tetramer. These chimaeric enzymes exhibit a significant increase in enzymatic activity upon binding of either monoclonal antibodies or sera directed against the inserted viral peptide. In JX772A but not in M278VP1, the Fab 3E5 antibody fragment promotes reactivation to the same extent as the complete antibody. On the other hand, M278VP1 K m is reduced by more than 50% in the presence of activating serum, this parameter remains invariable in JX772A and it is only slightly modified in JX795A. In these last two proteins, significant k cat variations can account for the increased enzymatic activity. Alternative reactivation mechanisms in the different β‐galactosidase probes are discussed in the context of the bacterial enzyme structure and its tolerance to antibody‐induced conformational modifications.

A recombinant, arginine-glycine-aspartic acid (RGD) motif from foot-and-mouth disease virus binds mammalian cells through vitronectin and, to a lower extent, fibronectin receptors

The cell-binding abilities of a recombinant, RGD-containing peptide from foot-and-mouth disease virus (FMDV) have been characterized in HeLa and BHK cells. This peptide represents the aa sequence of the solvent-exposed G-H loop of protein VP1 which is involved in cell recognition and infection. The efficiency of the viral motif in promoting cell attachment and spreading is comparable to that shown by fibronectin or vitronectin. Cell binding is inhibited by a monoclonal antibody directed against a viral, RGD-involving B-cell epitope and also by sera against vitronectin (alpha V beta 3/beta 5) and fibronectin (alpha 5 beta 1) receptors. In addition, a synthetic RGD peptide, which is a ligand for both integrins, prevents the cell binding mediated by the FMDV domain. These data demonstrate that the FMDV RGD motif is a potent ligand for cell-receptor integrins and sufficient to promote cell attachment to susceptible cells mainly through the vitronectin receptor.

An optimized ultrasonication protocol for bacterial cell disruption and recovery of β-galactosidase fusion proteins

In this work, we have developed and optimized an ultrasonication protocol for Escherichia coli recombinant cells, adapted to laboratory-scale release of β-galactosidase fusion proteins. After a single sonication treatment of 15 minutes, about 30% of recombinant protein present in the sample remains still associated to cellular debris, and it can not be removed by increasing the sonication time. After a clarification step a second sonication treatment of the resuspended cell debris again releases only a 70% of the remaining product. Therefore, the application of two short, consecutive sonication treatments permits a global recovery yield of about 90%. The use of a new disruption buffer to stabilize β-galactosidase allows the fusion proteins to maintain the active form throughout the process.

Enhanced response to antibody binding in engineered β-galactosidase enzymatic sensors

Peptide display on solvent-exposed surfaces of engineered enzymes allows them to respond to anti-peptide antibodies by detectable changes in their enzymatic activity, offering a new principle for biosensor development. In this work, we show that multiple peptide insertion in the vicinity of the Escherichia coli beta-galactosidase active site dramatically increases the enzyme responsiveness to specific anti-peptide antibodies. The modified enzymes HD7872A and HT7278CA, carrying eight and 12 copies respectively of a foot-and-mouth disease peptide per enzyme molecule, show antibody-mediated activation factors higher than those previously observed in the first generation enzymatic sensors, for HT7278CA being close to 400%. The analysis of the signal transduction process with multiple inserted proteins strongly suggests a new, non-exclusive mechanism of enzymatic regulation in which the target proteins might be stabilised by the bound antibody, extending the enzyme half-life and consequently enhancing the signal-background ratio. In addition, the tested sensors are differently responsive to sera from immune farm animals, depending on the antigenic similarity between the B-cell epitopes in the immunising virus and those in the peptide used as sensing element on the enzyme surface. Altogether, these results point out the utility of these enzymatic biosensors for a simple diagnosis of foot-and-mouth disease in an extremely fast homogeneous assay.

A cell adhesion peptide from foot‐and‐mouth disease virus can direct cell targeted delivery of a functional enzyme

The G-H loop of foot-and-mouth disease virus is a disordered protrusion of the VP1 protein exposed on the virion surface. This short stretch includes an arginine-glycine-aspartic acid tripeptide, a recognized integrin-binding motif, which is responsible for cell attachment and infection. Eight copies of a peptide reproducing the amino acid sequence of this FMDV ligand have been displayed in solvent-exposed regions on an enzymatically active recombinant beta-galactosidase. This viral peptide segment enables the chimeric enzyme to bind mammalian cell lines with different efficiencies, probably depending on the number of suitable cell receptors present on each of them. Moreover, it also promotes the internalization of the attached enzyme, which is transiently active inside the cells. These results suggest further exploration of the potential use of short adhesion peptides of viral origin as cell attachment tags to direct the targeted delivery of both genes and enzymes, instead of whole, infectious viruses.

REVERSIBLE ACTIVATION OF A CRYPTIC CLEAVAGE SITE WITHIN E. COLI BETA -GALACTOSIDASE IN BETA -GALACTOSIDASE FUSION PROTEINS

The VP60 capsid protein of rabbit haemorrhagic disease virus (60 kDa) has been fused to the C-terminus of beta-galactosidase and produced in E. coli from two related expression vectors. One of these vectors, carries a 429 bp DNA segment encoding the N-terminus peptide of VP60, and directs the synthesis of a larger fusion that contains the entire viral protein. Both fusion proteins are efficiently cleaved at a presumed trypsin-like target site within the carboxy moiety of beta-galactosidase (Arg 611-Thr 612), which is activated by the presence of the viral partner. In the larger fusion, VP60 is released by a cleavage within the linker region that affects about 10% of the chimeric proteins. In this situation, the resulting beta-galactosidase-like fragment recovers its natural proteolytic stability. These results prove that cryptic cleavage sites in beta-galactosidase can be efficiently activated in a fusion protein and suggest that this activation is based on reversible steric constraints generated by the fusion partner.

Corrigendum to: Distinct mechanisms of antibody-mediated enzymatic reactivation in β-galactosidase molecular sensors: [FEBS Letters 438 (1998) 267-271]

The authors had previously explored the reactivation mechanisms of three L-galactosidase-based enzymatic sensors, namely M278VP1, JX772A and JX795A. However, cross-contamination between the JX772A and JX795A protein stocks used for this purpose has since been noticed. After a carefully repeated analysis of new pure protein stocks, the authors have observed a very poor reactivation of JX772A upon antibody binding (within the experimental background) and have also determined new parameters for JX7795A, this enzyme clearly belonging to the class II sensors. These data are given in corrected Tables 1 and 2.