Extraction of recombinant protein from Escherichia coli by using a novel cell autolysis activity of VanX

Controllable Autolytic Leaky E. coli Platform for the Recovery of Intracellular Proteins

Escherichia coli is a commonly used platform for the production of heterologous proteins. Extraction and purification of intracellularly expressed recombinant proteins rely on efficient cell disruption. To facilitate downstream processing, controlled autolytic cells have been designed that lyse automatically to release intracellular proteins when triggered with an internal or external signal. In the cases when a weak promoter has to be adopted to control autolysis, cell lysis and product release progress slowly even in the presence of surfactants or other adjuvants. In this study, we report an improved autolytic E. coli strain controlled by a weak promoter with higher efficiency without the use of any facilitating chemical. Cell lysis was initiated upon arabinose-induced expression of T4 lysozyme with N-terminal fusion of amphipathic cell-penetrating peptides via a flexible peptide linker. Furthermore, genes involved in membrane permeability were individually deleted and screened for leaky phenotypes. Deletion of lpp (encoding Braun's lipoprotein) combined with the autolytic system caused 96% cell lysis in 4 h of induction and released 84% or 67% of mCherry or a super large Cas13a fusion protein (160.8 kDa), respectively, in 10 h of induction. This autolytic leaky strain shows great promise for protein recovery and library screening.

Engineering of bacteria towards programmed autolysis: why, how, and when?

Programmed autolytic bacteria, also termed controlled self-disruptive or self-destructive bacteria, are bacterial systems that express certain lytic genes and undergo cell lysis at a predetermined time point to release the intracellular contents or to commit suicide. Such systems have wide applications in high-throughput screening of protein libraries, synthesis and recovery of bio-products, population control of heterogeneous cultures or synthetic co-cultures, drug delivery, and food fermentation. Recently, great achievements have been reported regarding on-demand control of cell autolysis for different purposes, highlighting the potential of autolytic strains in biomanufacturing and biomedicine. In this review article, we first introduce the various applications of such bacteria, followed by a summarization of the approaches used in the establishment of autolytic bacterial systems, including cell autolysis mediated by cell wall hydrolases with or without facilitating proteins and by membrane-disturbing proteins. Next, we describe in detail the methodologies adopted to control and initiate cell lysis, including induction by chemical inducers, stimulation by physical signals, auto-induction by metabolic status or nutrient limitation, and constitutive expression of the lytic genes. This article is ended with discussions on the remaining problems and possible future directions. This review provides comprehensive information on autolytic bacteria and insightful guidance to the development of highly efficient, robust, and smart autolytic bacterial platforms.

Endolysin-Based Autolytic E. coli System for Facile Recovery of Recombinant Proteins

Recovery of recombinant proteins from the Escherichia coli cytoplasm depends on cell disruption by mechanical, chemical, and/or enzymatic methods, which usually cause incomplete cell breakage or protein denaturation. Controllable autolytic E. coli strains have been designed to facilitate the purification of recombinant proteins; however, these strains suffer from low recovery yield, slow cell lysis, or extensive strain engineering. Herein, we report an improved, highly efficient programmable autolytic E. coli platform, in which cell lysis is initiated upon the induced expression of T4 lysozyme with N-terminal fusion of a cell-penetrating peptide. Through the engineering of the peptide sequence and copy number, and by incorporating the fusion lytic gene into the E. coli genome, more than 99.97% of cells could be lysed within 30 min of induction regardless of cell age. We further tested the expression and release of a recombinant enzyme lysostaphin (Lst) and demonstrated that 4 h induction of the lytic gene after 3 h of Lst expression resulted in 98.97% cell lysis. Lst obtained from this system had the same yield, yet 1.63-fold higher activity, compared with that obtained from cells lysed by freeze-thawing and sonication. This autolytic platform shows potential for use in large-scale microbial production of proteins and other biopolymers.

A novel screening system based on VanX-mediated autolysis-Application to Gaussia luciferase

We report a novel bacterial screening protocol based on co-expressing the target protein with VanX, an enzyme which mediates Escherichia coli's autolysis and the release of the target protein into the culture medium, thereby facilitating activity measurement and screening from crude medium. This protocol as assessed with 19 Gaussia luciferase (GLuc) expressing colonies, was able to detect bioluminescence wavelength shift as small as 1.5 nm. We demonstrate the performance and versatility of this protocol by applying it to a semi-rational search for GLuc variants with red-shifted bioluminescence. Six GLuc's sites, F113, I114, W143, L144, A149, and F151, were randomly mutated, and for each site, 50 colonies were cultivated in 3 mL samples, from which bioluminescence was measured without purification. We identified two GLuc single mutation red-shifted variants: W143V and L144A. Their red shifted bioluminescence and biophysical/biochemical properties were confirmed using HPLC purified variants. Biotechnol. Bioeng. 2016;113: 1413-1420. © 2015 Wiley Periodicals, Inc.

Biochemical and biophysical characterization of an unexpected bacteriolytic activity of VanX, a member of the vancomycin-resistance vanA gene cluster

VanX is a d-alanyl-d-alanine (d-Ala-d-Ala) dipeptidase encoded in the vancomycin-resistance vanA gene cluster. Here we report that strong bacteriolysis occurred when isolated VanX was expressed in Escherichia coli at temperatures lower than 30 °C, which was unexpected because the vanA operon confers vancomycin resistance by protecting the cell wall. Therefore, we monitored cell lysis by measuring sample turbidity with absorbance at 590 nm and VanX expression using SDS-PAGE. No cell lysis was observed when VanX was expressed, even in large quantities, in the cell inclusion bodies at 37 °C, suggesting that a natively folded VanX is required for lysis. In addition, VanX mutants with suppressed dipeptidase activity did not lyse E. coli cells, confirming that bacteriolysis originated from the dipeptidase activity of VanX. We also observed shape changes in E. coli cells undergoing VanX-mediated lysis with optical microscopy and classified these changes into three classes: bursting, deformation, and leaking fluid. Optical microscopic image analysis fully corroborated our interpretation of the turbidity changes in the samples. From a practical perspective, the finding that VanX expressed in isolation induces cell lysis suggests that inhibitors of VanA and VanH that act downstream from VanX could provide a new class of therapeutic chemicals against bacteria expressing the vancomycin-resistance gene cluster.