Functional refolding of a recombinant C-type lectin-like domain containing intramolecular disulfide bonds

Characterization of a Molecularly Engineered Banlec-Type Lectin (rBTL)

Lectins are proteins that reversibly bind to carbohydrates and are commonly found across many species. The Banana Lectin (BanLec) is a member of the Jacalin-related Lectins, heavily studied for its immunomodulatory, antiproliferative, and antiviral activity. In this study, a novel sequence was generated in silico considering the native BanLec amino acid sequence and 9 other lectins belonging to JRL. Based on multiple alignment of these proteins, 11 amino acids of the BanLec sequence were modified because of their potential for interference in active binding site properties resulting in a new lectin named recombinant BanLec-type Lectin (rBTL). rBTL was expressed in E. coli and was able to keep biological activity in hemagglutination assay (rat erythrocytes), maintaining similar structure with the native lectin. Antiproliferative activity was demonstrated on human melanoma lineage (A375), evaluated by 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT). rBTL was able to inhibit cellular growth in a concentration-dependent manner, in an 8-h incubation, 12 µg/mL of rBTL led to a 28.94% of cell survival compared to cell control with 100%. Through a nonlinear fit out log-concentration versus biological response, an IC50% of 3.649 µg/mL of rBTL was determined. In conclusion, it is possible to state that the changes made to the rBTL sequence maintained the structure of the carbohydrate-binding site without changing specificity. The new lectin is biologically active, with an improved carbohydrate recognition spectrum compared to nBanLec, and can also be considered cytotoxic for A375 cells.

"Affimer" synthetic protein scaffolds block oxidized LDL binding to the LOX-1 scavenger receptor and inhibit ERK1/2 activation

In multicellular organisms, a variety of lipid-protein particles control the systemic flow of triacylglycerides, cholesterol, and fatty acids between cells in different tissues. The chemical modification by oxidation of these particles can trigger pathological responses, mediated by a group of membrane proteins termed scavenger receptors. The lectin-like oxidized low-density lipoprotein (LOX-1) scavenger receptor binds to oxidized low-density lipoprotein (oxLDL) and mediates both signaling and trafficking outcomes. Here, we identified five synthetic proteins termed Affimers from a phage display library, each capable of binding recombinant LOX-1 extracellular (oxLDL-binding) domain with high specificity. These Affimers, based on a phytocystatin scaffold with loop regions of variable sequence, were able to bind to the plasma membrane of HEK293T cells exclusively when human LOX-1 was expressed. Binding and uptake of fluorescently labeled oxLDL by the LOX-1-expressing cell model was inhibited with subnanomolar potency by all 5 Affimers. ERK1/2 activation, stimulated by oxLDL binding to LOX-1, was also significantly inhibited (p < 0.01) by preincubation with LOX-1-specific Affimers, but these Affimers had no direct agonistic effect. Molecular modeling indicated that the LOX-1-specific Affimers bound predominantly via their variable loop regions to the surface of the LOX-1 lectin-like domain that contains a distinctive arrangement of arginine residues previously implicated in oxLDL binding, involving interactions with both subunits of the native, stable scavenger receptor homodimer. These data provide a new class of synthetic tools to probe and potentially modulate the oxLDL/LOX-1 interaction that plays an important role in vascular disease.

Protamine may have anti-atherogenic potential by inhibiting the binding of oxidized-low density lipoprotein to LOX-1

Oxidized low-density lipoprotein (ox-LDL) leads to atherosclerosis via lectin-like oxidized lipoprotein receptor-1 (LOX-1), one of the major receptor for ox-LDL. Inhibition of the binding of ox-LDL to LOX-1 decreases the proinflammatory and atherosclerotic events. The aim of the present study was to investigate whether protamine, a polybasic nuclear protein, interferes the binding of ox-LDL to LOX-1. Using sandwich ELISA with newly generated antibody, we measured the blocking effect of protamine on the binding of ox-LDL to LOX-1. Protamine dose-dependently inhibited the binding of ox-LDL to LOX-1. DiI-labeled ox-LDL uptake assay in two types of cultured human endothelial cells was performed with fluorescence microplate reader. Activation of extracellular-signal-regulated kinase (ERK)1/2 by ox-LDL was analyzed by immunoblotting. We found that protamine suppressed uptake of ox-LDL in endothelial cells and inhibited ERK1/2 activation by ox-LDL. These results suggest that protamine may possess anti-atherogenic potential by inhibiting ox-LDL binding to LOX-1 through electrostatic interactions.

β-Cyclodextrin-Modified Magnetic Nanoparticles Immobilized on Sepharose Surface Provide an Effective Matrix for Protein Refolding

In this article, we propose an impressive and facile strategy to improve protein refolding using solid phase artificial molecular chaperones consisting of the surface-functionalized magnetic nanoparticles. Specifically, monotosyl-β-cyclodextrin connected to the surface of 3-aminopropyltriethoxysilane (APES)-modified magnetic nanoparticles is immobilized on the sepharose surface to promote interaction with exposed hydrophobic surfaces of partially folded (intermediates) and unfolded states of proteins. Their efficiencies were investigated by circular dichroism spectroscopy and photoluminescence spectroscopy of the protein. Although the mechanism of this method is based on principles of hydrophobic chromatography, this system is not only purging the native protein from inactive inclusion bodies but also improving the protein refolding process. We chose β-cyclodextrin (β-CD) considering multiple reports in the literature about its efficiency in protein refolding and its biocompatibility. To increase the surface area/volume ratio of the sepharose surface by nanoparticles, more β-CD molecules are connected to the sepharose surface to make a better interaction with proteins. We suppose that proteins are isolated in the nanospace created by bound cyclodextrins on the resin surface so intermolecular interactions are reduced. The architecture of nanoparticles was characterized by Fourier transform infrared spectra, X-ray diffraction, scanning electron microscopy images, energy dispersive X-ray spectroscopy, nuclear magnetic resonance (¹H NMR and ¹³C NMR), and dynamic light scattering.

The disulfide-rich Metridia luciferase refolded from E. coli inclusion bodies reveals the properties of a native folded enzyme produced in insect cells

The bioluminescence of a marine copepod Metridia longa is determined by a small secreted coelenterazine-dependent luciferase that uses coelenterazine as a substrate of enzymatic reaction to generate light (λ_max=480nm). To date, four different isoforms of the luciferase differing in size, sequences, and properties have been cloned by functional screening. All of them contain ten conserved Cys residues that suggests up to five SS intramolecular bonds per luciferase molecule. Whereas the use of copepod luciferases as bioluminescent reporters in biomedical research in vivo is growing from year to year, their application for in vitro assays is still limited by the difficulty in obtaining significant amounts of luciferase. The most cost-effective host for producing recombinant proteins is Escherichia coli. However, prokaryotic and eukaryotic cells maintain the reductive environment in cytoplasm that hinders the disulfide bond formation and consequently the proper folding of luciferase. Here we report the expression of the MLuc7 isoform of M. longa luciferase in E. coli cells and the efficient procedure for refolding from inclusion bodies yielding a high-active monomeric protein. Furthermore, in a set of identical experiments we demonstrate that bioluminescent and structural features of MLuc7 produced in bacterial cells are identical to those of MLuc7 isoform produced from culture medium of insect cells. Although the yield of high-purity protein is only 6mg/L, the application of E. coli cells to produce the luciferase is simpler and more cost-effective than the use of insect cells. We expect that the suggested technology of Metridia luciferase production allows obtaining of sufficient amounts of protein both for the development of novel in vitro analytical assays with the use of MLuc7 as a label and for structural studies.

Identification of 4-hydroxy-2-nonenal–histidine adducts that serve as ligands for human lectin-like oxidized LDL receptor-1

LOX-1 (lectin-like oxidized low-density lipoprotein receptor-1) is an endothelial scavenger receptor that is important for the uptake of OxLDL (oxidized low-density lipoprotein) and contributes to the pathogenesis of atherosclerosis. However, the precise structural motifs of OxLDL that are recognized by LOX-1 are unknown. In the present study, we have identified products of lipid peroxidation of OxLDL that serve as ligands for LOX-1. We used CHO (Chinese-hamster ovary) cells that stably express LOX-1 to evaluate the ability of BSA modified by lipid peroxidation to compete with AcLDL (acetylated low-density lipoprotein). We found that HNE (4-hydroxy-2-nonenal)-modified proteins most potently inhibited the uptake of AcLDL. On the basis of the findings that HNE-modified BSA and oxidation of LDL resulted in the formation of HNE–histidine Michael adducts, we examined whether the HNE–histidine adducts could serve as ligands for LOX-1. The authentic HNE–histidine adduct inhibited the uptake of AcLDL in a dose-dependent manner. Furthermore, we found the interaction of LOX-1 with the HNE–histidine adduct to have a dissociation constant of 1.22×10−8 M using a surface plasmon resonance assay. Finally, we showed that the HNE–histidine adduct stimulated the formation of reactive oxygen species and activated extracellular-signal-regulated kinase 1/2 and NF-κB (nuclear factor κB) in HAECs (human aortic endothelial cells); these signals initiate endothelial dysfunction and lead to atherosclerosis. The present study provides intriguing insights into the molecular details of LOX-1 recognition of OxLDL.

Lectin-like oxidized low-density lipoprotein receptor-1 delivers heat shock protein 60-fused antigen into the MHC class I presentation pathway

Heat shock protein (Hsp) 60 elicits a potent proinflammatory response in the innate immune system and has been proposed as a danger signal of stressed or damaged cells to the immune system. Previous studies reported CD14, TLR2, and TLR4 as mediators of signaling but probably not of binding. Although the receptor for Hsp60 was proposed to be saturable and specific on macrophages, it is not well defined. In the current study, we found that lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), as a receptor for Hsp60, could bind and internalize Hsp60 via the C terminus of Hsp60. Yeast two-hybrid assay revealed that the second beta-sheet containing the long-loop region of LOX-1 played an important role in this interaction. Furthermore, LOX-1 might be engaged as a common receptor for different Hsp60 species. Bone marrow-derived dendritic cells could cross-present Hsp60-fused OVA Ag on MHC class I molecules via LOX-1. Inhibition of the recognition of Hsp60 by LOX-1 decreases Hsp60-mediated cross-presentation of OVA and specific CTL response and protective tumor immunity in vivo. Taken together, these results demonstrate that LOX-1 functions as a receptor for Hsp60 and is involved in the delivery of Hsp60-fused Ag into the MHC class I presentation pathway.

Junctin and triadin each activate skeletal ryanodine receptors but junctin alone mediates functional interactions with calsequestrin

Normal Ca(2+) signalling in skeletal muscle depends on the membrane associated proteins triadin and junctin and their ability to mediate functional interactions between the Ca(2+) binding protein calsequestrin and the type 1 ryanodine receptor in the lumen of the sarcoplasmic reticulum. This important mechanism conserves intracellular Ca(2+) stores, but is poorly understood. Triadin and junctin share similar structures and are lumped together in models of interactions between skeletal muscle calsequestrin and ryanodine receptors, however their individual roles have not been examined at a molecular level. We show here that purified skeletal ryanodine receptors are similarly activated by purified triadin or purified junctin added to their luminal side, although a lack of competition indicated that the proteins act at independent sites. Surprisingly, triadin and junctin differed markedly in their ability to transmit information between skeletal calsequestrin and ryanodine receptors. Purified calsequestrin inhibited junctin/triadin-associated, or junctin-associated, ryanodine receptors and the calsequestrin re-associated channel complexes were further inhibited when luminal Ca(2+) fell from 1mM to <or=100 microM, as seen with native channels (containing endogenous calsequestrin/triadin/junctin). In contrast, skeletal calsequestrin had no effect on the triadin/ryanodine receptor complex and the channel activity of this complex increased when luminal Ca(2+) fell, as seen with purified channels prior to triadin/calsequestrin re-association. Therefore in this cell free system, junctin alone mediates signals between luminal Ca(2+), skeletal calsequestrin and skeletal ryanodine receptors and may curtail resting Ca(2+) leak from the sarcoplasmic reticulum. We suggest that triadin serves a different function which may dominate during excitation-contraction coupling.

An engineered complement receptor 1 composed of two functional domains can protect against immune-mediated hemolysis

Complement receptor type 1 (CR1) is a versatile inhibitor of both classical and alternative pathway C3 and C5 convertases with an ability to accelerate decay activity and act as a co-factor in C3b/C4b cleavage. In order to develop a short form of CR1 with similar biological activities to the full-length human CR1, we combined functional domain 1, located in the long homologous repeat (LHR) A, with functional domain 2, located in LHR C. We expressed the two-domain, two-function protein with an enterokinase site at the N-terminus and a termination codon at the C-terminus in Escherichia coli. The fusion protein was purified on a Ni-NTA-agarose column. After subsequent refolding, the recombinant CR1-derivative protein was obtained by enterokinase cleavage and subsequent purification. In vitro, the recombinant CR1-derivative reduced hemolysis, C5a release and surface C3 deposition. It was also effective in prolonging survival of transfused incompatible red blood cells in vivo. Our results indicate that the CR1-based protein may be a model for developing smaller and more potent complement inhibitors for future therapeutics.

Oxidised LDL internalisation by the LOX-1 scavenger receptor is dependent on a novel cytoplasmic motif and is regulated by dynamin-2

The LOX-1 scavenger receptor recognises pro-atherogenic oxidised low-density lipoprotein (OxLDL) particles and is implicated in atherosclerotic plaque formation, but this mechanism is not well understood. Here we show evidence for a novel clathrin-independent and cytosolic-signal-dependent pathway that regulates LOX-1-mediated OxLDL internalisation. Cell surface labelling in the absence or presence of OxLDL ligand showed that LOX-1 is constitutively internalised from the plasma membrane and its half-life is not altered upon ligand binding and trafficking. We show that LOX-1-mediated OxLDL uptake is disrupted by overexpression of dominant-negative dynamin-2 but unaffected by CHC17 or mu2 (AP2) depletion. Site-directed mutagenesis revealed a conserved and novel cytoplasmic tripeptide motif (DDL) that regulates LOX-1-mediated endocytosis of OxLDL. Taken together, these findings indicate that LOX-1 is internalised by a clathrin-independent and dynamin-2-dependent pathway and is thus likely to mediate OxLDL trafficking in vascular tissues.