Corin is a cardiac transmembrane serine protease. In cell-based studies, corin converted pro-atrial natriuretic peptide (pro-ANP) to mature ANP, suggesting that corin is potentially the pro-ANP convertase. In this study, we evaluated the importance of the transmembrane domain and activation cleavage in human corin. We showed that a soluble corin that consists of only the extracellular domain was capable of processing recombinant human pro-ANP in cell-based assays. In contrast, a mutation at the conserved activation cleavage site, R801A, abolished the function of corin, demonstrating that the activation cleavage is essential for corin activity. These results allowed us to design, express, and purify a mutant soluble corin, EKsolCorin, that contains an enterokinase recognition sequence at the activation cleavage site. Purified EKsolCorin was activated by enterokinase in a dose-dependent manner. Activated EKsolCorin had hydrolytic activity toward peptide substrates with a preference for Arg and Lys residues in the P-1 position. This activity of EKsolCorin was inhibited by trypsin-like serine protease inhibitors but not inhibitors of chymotrypsin-like, cysteine-, or metallo-proteases. In pro-ANP processing assays, purified active EKsolCorin converted recombinant human pro-ANP to biologically active ANP in a highly sequence-specific manner. The pro-ANP processing activity of EKsolCorin was not inhibited by human plasma. Together, our data indicate that the transmembrane domain is not necessary for the biological activity of corin but may be a mechanism to localize corin at specific sites, whereas the proteolytic cleavage at the activation site is an essential step in controlling the activity of corin.Corin is a mosaic serine protease that was recently identified from the human heart (1, 2). It consists of 1,042 amino acids and contains an integral transmembrane domain near the N terminus. In the extracellular region of corin, there are two frizzled-like cysteine-rich domains, eight low density lipoprotein receptor type A repeats, a scavenger receptor-like cysteinerich domain, and a C-terminal trypsin-like protease domain. Topologically, corin belongs to the newly defined type II transmembrane serine protease family (3-6), which includes enterokinase (EK) 1 (7), hepsin (8), matriptases (9 -12), TMPRSS2-5 (13-16), human airway trypsin-like protease (17), MSPL (18), DESC1 (19), and polyserase-I (20). The combination of domains present in corin, however, is unique among the trypsin-like serine proteases, because corin is the only serine protease identified so far that contains frizzled-like cysteinerich domains. Corin mRNA and protein are abundantly expressed in the heart (1, 2), suggesting that corin might have a role in the cardiovascular system. In cell-based experiments, we showed that recombinant human corin mediated the conversion of proatrial natriuretic peptide (pro-ANP) and pro-brain natriuretic peptide to mature ANP and brain natriuretic peptide (21), both of which are cardiac hormones important in maintaining ...

Cell‐free protein synthesis (CFPS) systems allow for robust protein expression with easy manipulation of conditions to improve protein yield and folding. Recent technological developments have significantly increased the productivity and reduced the operating costs of CFPS systems, such that they can compete with conventional in vivo protein production platforms, while also offering new routes for the discovery and production of biotherapeutics. As cell‐free systems have evolved, productivity increases have commonly been obtained by addition of components to previously designed reaction mixtures without careful re‐examination of the essentiality of reagents from previous generations. Here we present a systematic sensitivity analysis of the components in a conventional Escherichia coli CFPS reaction mixture to evaluate their optimal concentrations for production of the immunoglobulin G trastuzumab. We identify eight changes to the system, which result in optimal expression of trastuzumab. We find that doubling the potassium glutamate concentration, while entirely eliminating pyruvate, coenzyme A, NAD, total tRNA, folinic acid, putrescine and ammonium glutamate, results in a highly productive cell‐free system with a 95% reduction in reagent costs (excluding cell‐extract, plasmid, and T7 RNA polymerase made in‐house). A larger panel of other proteins was also tested and all show equivalent or improved yields with our simplified system. Furthermore, we demonstrate that all of the reagents for CFPS can be combined in a single freeze‐thaw stable master mix to improve reliability and ease of use. These improvements are important for the application of the CFPS system in fields such as protein engineering, high‐throughput screening, and biotherapeutics. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 31:823–831, 2015

Selection technologies such as ribosome display enable the rapid discovery of novel antibody fragments entirely in vitro. It has been assumed that the open nature of the cell-free reactions used in these technologies limits selections to single-chain protein fragments. We present a simple approach for the selection of multi-chain proteins, such as antibody Fab fragments, using ribosome display. Specifically, we show that a two-chain trastuzumab (Herceptin) Fab domain can be displayed in a format which tethers either the heavy or light chain to the ribosome while retaining functional antigen binding. Then, we constructed synthetic Fab HC and LC libraries and performed test selections against carcinoembryonic antigen (CEA) and vascular endothelial growth factor (VEGF). The Fab selection output was reformatted into full-length immunoglobulin Gs (IgGs) and directly expressed at high levels in an optimized cell-free system for immediate screening, purification and characterization. Several novel IgGs were identified using this cell-free platform that bind to purified CEA, CEA positive cells and VEGF.

Amber codon suppression for the insertion of non-natural amino acids (nnAAs) is limited by competition with release factor 1 (RF1). Here we describe the genome engineering of a RF1 mutant strain that enhances suppression efficiency during cell-free protein synthesis, without significantly impacting cell growth during biomass production. Specifically, an out membrane protease (OmpT) cleavage site was engineered into the switch loop of RF1, which enables its conditional inactivation during cell lysis. This facilitates extract production without additional processing steps, resulting in a scaleable extract production process. The RF1 mutant extract allows nnAA incorporation at previously intractable sites of an IgG1 and at multiple sites in the same polypeptide chain. Conjugation of cytotoxic agents to these nnAAs, yields homogeneous antibody drug conjugates (ADCs) that can be optimized for conjugation site, drug to antibody ratio (DAR) and linker-warheads designed for efficient tumor killing. This platform provides the means to generate therapeutic ADCs inaccessible by other methods that are efficient in their cytotoxin delivery to tumor with reduced dose-limiting toxicities and thus have the potential for better clinical impact.

Antibody drug conjugates (ADCs) harness the target specificity of a monoclonal antibody (mAb) and the high cytotoxicity of a small molecule, enabling improved delivery of a potent antitumor agent compared to traditional chemotherapy for cancer therapy. Only two ADCs have been marketed, both of which are produced via nonsite-specific conjugation of the cytotoxic drug to either interchain cysteine (Adcetris) or lysine (Kadcyla). A growing body of evidence suggests that site-specific ADCs, because of their payload homogeneity, will improve pharmacokinetics and have wider therapeutic windows when compared to heterogeneous ADCs. Previously, we have demonstrated the use of a cell free expression system (Xpress CF+) for rapid production of site-specific ADCs. Here we report the generation of a variety of ADCs via conjugation between a site-specific incorporated non-natural amino acid (nnAA), para-azidomethyl-l-phenylalanine (pAMF), and dibenzocyclooctyl-(polyethylene glycol)4 (DBCO-(PEG)4) linked payloads using this platform. We developed a reversed phase HPLC method for drug to antibody ratio (DAR) characterization, which is applicable to both reduced and intact ADCs. We demonstrate that these ADCs are of near complete conjugation and exhibit potent cell killing activity and in vitro plasma stability. Moreover, we generated an ADC conjugated at both light and heavy chains, resulting in a DAR close to 4. With the increased number of payloads, the resultant DAR 4 ADC is potentially more efficacious than its DAR 2 counterparts, which could further improve its therapeutic index. These studies have demonstrated the competency of Xpress CF+ for site-specific ADC production and improved our understanding of the site-specific ADCs in general.