Chaperone-like effect of monoclonal antibodies on refolding of heat-denatured carboxypeptidase A

Antichaperone activity and heme degradation effect of methyl tert-butyl ether (MTBE) on normal and diabetic hemoglobins

Because of the extensive use of methyl tert-butyl ether (MTBE) as an additive to increase the octane quality of gasoline, the environmental pollution by this compound has increased in recent decades. Environmental release of MTBE may lead to its entry to the blood stream through inhalation or drinking of contaminated water, and its interactions with biological molecules such as proteins. The present study was proposed to comparatively investigate the interactions of MTBE with hemoglobin (Hb) from diabetic and nondiabetic individuals using various spectroscopic methods including UV-visible, fluorescence, chemiluminescence, and circular dichroism. These results demonstrated the effects of MTBE on heme degradation of Hb and the reaction of these degradation products with water generating reactive oxygen species. Interaction of Hb with MTBE enhanced its aggregation rate and decreased lag time, indicating the antichaperone activity of MTBE upon interaction with Hb. Furthermore, the diabetic Hb showed more severe effects of MTBE, including heme degradation, reactive oxygen species production, unfolding, and antichaperone behavior than the nondiabetic Hb. The results from molecular docking suggested that the special interaction site of MTBE in the vicinity of Hb heme group is responsible for heme degradation.

Designing an Antibody-Based Chaperoning System through Programming the Binding and Release of the Folding Intermediate

The protein folding pathway consists of sequential intramolecular interactions, while chaperones exert their functions either by stabilizing folding intermediates or by preventing nonspecific intermolecular interactions, which are often associated with aggregation involving exposed hydrophobic residues in folding intermediates. As chaperones do not possess specificity for individual client proteins, we designed an antibody-based chaperoning system to mimic the sequential binding and release of client proteins undergoing folding. The single-chain variable fragment of antibody (scFv) A4 binds to human muscle creatine kinase (HCK) and prevents it from aggregating. The slow dissociation of HCK from A4 resulted in delayed but eventually high-quality refolding, as reflected by the higher recovery of enzymatic activity as well as abolished aggregation. Peptide P6, a sequence in HCK involved in A4 binding, competes with HCK, promotes its dissociation from A4, and accelerates the rate of high-quality refolding. The sequential addition of A4 and P6 is essential for the chaperoning effect. The programmed binding/release method can also be applied to refold HCK from inclusion bodies. Because the association/dissociation of the folding intermediate with the antibody is highly specific, the method can be used to design tailored refolding systems and to investigate chaperoning effects on protein folding/aggregation in a sequence-specific manner.

Angiotensin I-converting enzyme Gln1069Arg mutation impairs trafficking to the cell surface resulting in selective denaturation of the C-domain

Background

Angiotensin-converting enzyme (ACE; Kininase II; CD143) hydrolyzes small peptides such as angiotensin I, bradykinin, substance P, LH-RH and several others and thus plays a key role in blood pressure regulation and vascular remodeling. Complete absence of ACE in humans leads to renal tubular dysgenesis (RTD), a severe disorder of renal tubule development characterized by persistent fetal anuria and perinatal death.

Methodology/Principal Findings

Patient with RTD in Lisbon, Portugal, maintained by peritoneal dialysis since birth, was found to have a homozygous substitution of Arg for Glu at position 1069 in the C-terminal domain of ACE (Q1069R) resulting in absence of plasma ACE activity; both parents and a brother who are heterozygous carriers of this mutation had exactly half-normal plasma ACE activity compared to healthy individuals. We hypothesized that the Q1069R substitution impaired ACE trafficking to the cell surface and led to accumulation of catalytically inactive ACE in the cell cytoplasm. CHO cells expressing wild-type (WT) vs. Q1069R-ACE demonstrated the mutant accumulates intracellularly and also that it is significantly degraded by intracellular proteases. Q1069R-ACE retained catalytic and immunological characteristics of WT-ACE N domain whereas it had 10–20% of the nativity of the WT-ACE C domain. A combination of chemical (sodium butyrate) or pharmacological (ACE inhibitor) chaperones with proteasome inhibitors (MG 132 or bortezomib) significantly restored trafficking of Q1069R-ACE to the cell surface and increased ACE activity in the cell culture media 4-fold.

Conclusions/Significance

Homozygous Q1069R substitution results in an ACE trafficking and processing defect which can be rescued, at least in cell culture, by a combination of chaperones and proteasome inhibitors. Further studies are required to determine whether similar treatment of individuals with this ACE mutation would provide therapeutic benefits such as concentration of primary urine.

Clinical immunologic approaches for the treatment of Alzheimer's disease

Recent clinical trials of active vaccination against beta-amyloid (Abeta) have succeeded in clearing Abeta plaques; however, further understanding of immunization with regards to inflammation and other hallmarks of Alzheimer's disease pathology is required. Antibodies generated with this first-generation vaccine may not have had the desired therapeutic properties or targeted the 'correct' mechanism, but they have opened the way for new clinical approaches, which are now under consideration. Passive administration of monoclonal antibodies directed to various regions of Abeta peptide and/or administration of immunoconjugates of only small fragments of the N-terminal region may lead to the development of an improved second generation of Abeta vaccines. Amyloid immunotherapy offers genuine opportunities for disease treatment; however, such an approach towards treating and preventing Alzheimer's disease patients requires careful antigen and antibody selection to maximize efficacy and minimize adverse events.

Inactivation and modification of superoxide dismutase by glyoxal: Prevention by antibodies

Glyoxal is an endogenous compound, the levels of which are increased in various pathologies associated with hyperglycaemia and other related disorders. It has been reported to inactivate critical cellular enzymes by promoting their cross-linking and perpetuates advanced glycation end-product (AGE) formation. In this study, we used superoxide dismutase (SOD) as a model to investigate the ability of specific anti-enzyme antibodies and monomer Fab fragments to protect against glyoxal-induced deactivation and aggregate formation. We found that glyoxal deactivated SOD, in a concentration and time-dependent fashion. The enzymatic activity was monitored spectrophotometrically and it was found that enzyme lost approximately 95% of its original activity, when exposed to 10 mM glyoxal for 120 h. SDS-polyacrylamide gel electrophoresis demonstrated the formation of high molecular weight aggregates in SOD samples exposed to glyoxal. Surface-enhanced laser desorption/ionization time of flight mass spectrometry (SELDI-TOF-MS) showed increase in relative molecular mass (M(r)), upon exposure to glyoxal. Specific anti-enzyme antibodies and monomer Fab fragments markedly inhibited SOD deactivation caused by glyoxal and decreased the extent of cross-linking or formation of aggregates. This protection by the antibodies or Fab fragments was specific since, other non-specific antibodies were not able to protect SOD. Previously, antibodies have been used to prevent aggregation of beta-amyloid peptides in Alzheimer and prion-protein disease. Our findings provide a new perspective, for use of antibodies to prevent the biomolecules against glycation-induced deactivation and alteration.

Antibodies as specific chaperones

Protein folding is often accompanied by formation of non-native conformations leading to protein aggregation. A number of reports indicate that antibodies can facilitate folding and prevent aggregation of protein antigens. The influence of antibodies on folding is strictly antigen specific. Chaperone-like antibody activity may be due to the stabilization of native antigen conformations or folding transition states, or screening of aggregating hydrophobic surfaces. Taking advantage of chaperone-like activity of antibodies for immunotherapy may prove to be a promising approach to the treatment of Alzheimer's and prion-related diseases. Antibody-assisted folding may enhance renaturation of recombinant proteins from inclusion bodies.

Immunological approaches as therapy for Alzheimer's disease

The pathology of Alzheimer's disease (AD) shows a significant correlation between beta-amyloid peptide (AbetaP) conformation and the clinical severity of dementia. For many years, efforts have been focused on the development of inhibitors of beta-amyloid (Abeta) formation and its related neurotoxic effects. The author has developed a new concept showing that site-directed antibodies may modulate formation of Abeta. The performance of anti-Abeta antibodies in transgenic mice models of AD showed that they are delivered to the central nervous system (CNS), preventing in vivo formation of Abeta. Moreover, these antibodies dissolve Abeta plaques and protect the mice from learning difficulties and age-related memory deficits. Experimental active immunisation with Abeta (1-42) in humans has been stopped in Phase II of their clinical trials. However, several new preparations, able to provide antibodies against Abeta by either active or passive routes, have been formulated and at least one of these is likely to reach clinical testing. These data support the hypothesis that AbetaP plays a central role in AD and antibodies which modulate Abeta conformation may lead to immunotherapy of the disease.

Immunotherapeutic strategies for prevention and treatment of Alzheimer's disease

Pathologic examination in Alzheimer's disease (AD) shows a significant correlation between beta-amyloid peptide (AbetaP) deposition and the clinical severity of dementia. Formation of beta-amyloid (Abeta) is a complex kinetic and thermodynamic process, dependent on peptide-peptide interactions that may be modulated by other proteins. We found that site-directed antibodies toward peptide EFRH sequences 3-6 of the N-terminal region of AbetaP suppress in vitro formation of Abeta and dissolve already-formed fibrillar amyloid. These so-called chaperone-like properties of monoclonal antibodies led to the development of a new immunologic approach to AD treatment. The immunization procedure, based on phages displaying the EFRH epitope as antigen, induced anti-AbetaP antibodies that recognized the whole AbetaP and exhibited antiaggregating properties similar to those of antibodies obtained by injection of Abeta fibrils. Production and performance of anti-beta-amyloid antibodies in the transgenic mouse model of AD showed that these antibodies may be delivered from the periphery to the central nervous system, preventing the formation of Abeta and dissolving already-present aggregates. Moreover, immunization with Abeta protected transgenic mice from the learning and age-related memory deficits that occur in AD. These data support the hypotheses that Abeta plays a central role in AD and that site-directed antibodies that modulate Abeta conformation may provide immunotherapy of the disease.

Immunomodulation of the human prion peptide 106-126 aggregation

Site-directed monoclonal antibodies (mAbs) may interact with their antigens, leading to stabilization, refolding, and suppression of aggregation. In the following study, we show that mAbs raised against the peptide 106-126 of human prion protein (PrP 106-126) modulate the conformational changes occurring in the peptide exposed to aggregation conditions. MAbs 3-11 and 2-40 prevent PrP 106-126's fibrillar aggregation, disaggregates already formed aggregates, and inhibits the peptide's neurotoxic effect on the PC12 cells system, while mAb 3F4 has no protective effect. We suggest that there are key positions within the PrP 106-126 molecule where unfolding is initiated and their locking with specific antibodies may maintain the prion peptide native structure, reverse the aggregated peptide conformation, and lead to rearrangements involved in the essential feature of prion diseases.

High affinity binding of monoclonal antibodies to the sequential epitope EFRH of beta-amyloid peptide is essential for modulation of fibrillar aggregation

Monoclonal antibodies raised against the N-terminal of Alzheimer's beta-amyloid peptide (betaAP) were found to modulate its fibrillar aggregation. While mAbs 6C6 and 10D5 inhibit the formation of beta-amyloid fibrils, trigger disaggregation and reversal to its non-toxic form, mAb 2H3 is devoid of these properties. MAb 2H3 binds the sequence DAEFRHD, corresponding to position 1-7 of the betaAP with high affinity (2 x 10(-9) M) similar to its binding with the whole betaAP. The EFRH peptide strongly inhibits binding of mAbs 6C6 and 10D5 to betaAP, whereas it inhibits weakly the interaction of 2H3 with betaAP. Low affinity binding of mAb 2H3 to EFRH might explain its failure in prevention of beta-amyloid formation.

Bioaffinity based immobilization of enzymes

Procedures that utilize the affinities of biomolecules and ligands for the immobilization of enzymes are gaining increasing acceptance in the construction of sensitive enzyme-based analytical devices as well as for other applications. The strong affinity of polyclonal/monoclonal antibodies for specific enzymes and those of lectins for glycoenzymes bearing appropriate oligosaccharides have been generally employed for the purpose. Potential of affinity pairs like cellulose-cellulose binding domain bearing enzymes and immobilized metal ionsurface histidine bearing enzymes has also been recognised. The bioaffinity based immobilization procedures usually yield preparations exhibiting high catalytic activity and improved stability against denaturation. Bioaffinity based immobilizations are usually reversible facilitating the reuse of support matrix, orient the enzymes favourably and offer the possibility of enzyme immobilization directly from partially pure enzyme preparations or even cell lysates. Enzyme lacking innate ability to bind to various affinity supports can be made to bind to them by chemically or genetically linking the enzymes with appropriate polypeptides/domains like the cellulose binding domain, protein A, histidine-rich peptides, single chain antibodies, etc.

Disaggregation of Alzheimer beta-amyloid by site-directed mAb

In Alzheimer disease, beta-amyloid peptide accumulates in the brain as insoluble amyloid plaques. Amyloid filaments, similar to those found in amyloid plaques, can be assembled in vitro from chemically synthesized beta-peptides. In this study, we report that antibodies raised against the N-terminal region (1-28) of the beta-amyloid peptide bind to the in vitro-formed beta-amyloid assemblies, leading to disaggregation of the fibrils and partial restoration of the peptide's solubility. The concomitant addition of fibrillar beta-amyloid with these antibodies to PC 12 cells leads to the inhibition of the neurotoxic effects of beta-amyloid. Some of the mAbs raised against soluble beta-peptide (1-28) have been found to prevent in vitro fibrillar aggregation of beta-amyloid peptide. These experimental data suggest that site-directed mAbs interfere with the aggregation of beta-amyloid and trigger reversal to its nontoxic, normal components. The above findings give hints on how to convert in vivo senile plaques into nontoxic, diffuse components and may have therapeutic interest for those studying Alzheimer disease and other human diseases related to amyloidogenic properties of physiological peptides and proteins.

Conformation of P22 tailspike folding and aggregation intermediates probed by monoclonal antibodies

The partitioning of partially folded polypeptide chains between correctly folded native states and off-pathway inclusion bodies is a critical reaction in biotechnology. Multimeric partially folded intermediates, representing early stages of the aggregation pathway for the P22 tailspike protein, have been trapped in the cold and isolated by nondenaturing polyacrylamide gel electrophoresis (PAGE) (speed MA, Wang DIC, King J. 1995. Protein Sci 4:900-908). Monoclonal antibodies against tailspike chains discriminate between folding intermediates and native states (Friguet B, Djavadi-Ohaniance L, King J, Goldberg ME. 1994. J Biol Chem 269:15945-15949). Here we describe a nondenaturing Western blot procedure to probe the conformation of productive folding intermediates and off-pathway aggregation intermediates. The aggregation intermediates displayed epitopes in common with productive folding intermediates but were not recognized by antibodies against native epitopes. The nonnative epitope on the folding and aggregation intermediates was located on the partially folded N-terminus, indicating that the N-terminus remained accessible and nonnative in the aggregated state. Antibodies against native epitopes blocked folding, but the monoclonal directed against the N-terminal epitope did not, indicating that the conformation of the N-terminus is not a key determinant of the productive folding and chain association pathway.

Monoclonal antibodies inhibit in vitro fibrillar aggregation of the Alzheimer beta-amyloid peptide

The beta-amyloid peptide, the hallmark of Alzheimer disease, forms fibrillar toxic aggregates in brain tissue that can be dissolved only by strong denaturing agents. To study beta-amyloid formation and its inhibition, we prepared immune complexes with two monoclonal antibodies (mAbs), AMY-33 and 6F/3D, raised against beta-amyloid fragments spanning amino acid residues 1-28 and 8-17 of the beta-amyloid peptide chain, respectively. In vitro aggregation of beta-amyloid peptide was induced by incubation for 3 h at 37 degrees C and monitored by ELISA, negative staining electron microscopy, and fluorimetric studies. We found that the mAs prevent the aggregation of beta-amyloid peptide and that the inhibitory effect appears to be related to the localization of the antibody-binding sites and the nature of the aggregating agents. Preparation of mAbs against "aggregating epitopes," defined as sequences related to the sites where protein aggregation is initiated, may lead to the understanding and prevention of protein aggregation. The results of this study may provide a foundation for using mAbs in vivo to prevent the beta-amyloid peptide aggregation that is associated with Alzheimer disease.

The prosegment-subtilisin BPN' complex: crystal structure of a specific 'foldase'

BACKGROUND

The folding of the bacterial protease subtilisin BPN' (SBT) is dependent on its 77-residue prosegment, which is then autocatalytically removed to give the mature enzyme. Mature subtilisin represents a class of proteins that lacks an efficient folding pathway. Refolding of mature SBT is extremely slow unless catalyzed by the independently expressed prosegment, leading to a bimolecular complex.

RESULTS

We report the crystal structure at 2.0 A resolution of the prosegment-SBT complex and consider its implications for prosubtilisin BPN' maturation and folding catalysis. The prosegment forms a compact domain that binds SBT through an extensive interface involving the enzyme's two parallel surface helices (residues 104-116 and 133-144), supplying negatively charged caps to the N termini of these helices. The prosegment C terminus binds in the enzyme active site in a product-like manner, with Tyr77 in the P1 binding pocket.

CONCLUSIONS

The structure of the complex supports a unimolecular mechanism for prosubtilisin cleavage, involving a 25 A rearrangement of the SBT N terminus in a late folding step. A mechanism of folding catalysis in which the two helices and their connecting beta strand form a prosegment-stabilized folding nucleus is proposed. While this putative nucleus is stabilized by prosegment binding, the N-terminal and C-terminal subdomains of SBT could fold by propagation.