Butyrylcholinesterase Variants Research Articles

Gulf war illness: a tale of two genomes

IntroductionGulf War illness (GWI) is an environmentally-triggered chronic multisymptom illness typified by protean symptoms, in which mitochondrial impairment is evident. It has been likened to accelerated aging. Nuclear genetics of detoxification have been linked to GWI.ObjectiveTo see whether mitochondrial (mt) haplogroup U – a heritable profile of mitochondrial DNA that has been tied to aging-related conditions – significantly predicts greater GWI severity; and to assess whether GWI severity is influenced by mitochondrial as well as nuclear genetics. 54 consenting Gulf War veterans gave information on GWI severity, of whom 52 had nuclear DNA assessment; and 45 had both nuclear and mitochondrial DNA assessments. Regression with robust standard errors assessed prediction of GWI severity as a function of nuclear genetics (butyrylcholinesterase variants), mitochondrial genetics (haplogroup U, previously tied to aging-related conditions); or both.ResultsBChE “adverse” variants significantly predicted GWI severity (β(SE) = 23.4(11.4), p = 0.046), as did mt haplogroup U (β(SE) = 36.4(13.6), p = 0.010). In a model including both, BChE was no longer significant, but mt haplogroup U retained significance (β(SE) = 36.7(13.0), p = 0.007). This is the first study to show that mitochondrial genetics are tied to GWI severity in Gulf-deployed veterans. Other data affirm a tie to nuclear genetics, making GWI indeed a “tale of two genomes.”

Review of Genetic Variants of Butyrylcholinesterase and Their Potential Impact on Human Health

Butyrylcholinesterase (BChE) is an enzyme found in plasma and many other parts of the body. It is enzyme that hydrolyses drugs containing ester bonds such as drugs acting at the neuromuscular junction (succinylcholine) and local anaesthetics (procaine). Examination of the gene for mutations or polymorphisms causing the observed biochemical phenotypes has isolated those responsible for all the most widely known variants. The molecular bases of several genetic variants of BChE have been reported, such as the Atypical variant, fluoride-resistant variant, silent variant, K variant, J variant and C5 variant. In general, BChE polymorphisms have been shown to produce enzymes with varying levels of catalytic activity. Genetic variants of human butyrylcholinesterase were one of the first examples in the new field of pharmacogenetics when it was recognized that abnormal response to the succinylcholine was due to a mutated enzyme with low binding affinity. Beside that, variant of BChE has potential impact for Alzheimer disease patology.

Review of Genetic Variants of Butyrylcholinesterase and Their Potential Impact on Human Health

Butyrylcholinesterase (BChE) is an enzyme found in plasma and many other parts of the body. It is enzyme that hydrolyses drugs containing ester bonds such as drugs acting at the neuromuscular junction (succinylcholine) and local anaesthetics (procaine). Examination of the gene for mutations or polymorphisms causing the observed biochemical phenotypes has isolated those responsible for all the most widely known variants. The molecular bases of several genetic variants of BChE have been reported, such as the Atypical variant, fluoride-resistant variant, silent variant, K variant, J variant and C5 variant. In general, BChE polymorphisms have been shown to produce enzymes with varying levels of catalytic activity. Genetic variants of human butyrylcholinesterase were one of the first examples in the new field of pharmacogenetics when it was recognized that abnormal response to the succinylcholine was due to a mutated enzyme with low binding affinity. Beside that, variant of BChE has potential impact for Alzheimer disease patology.

Review of Genetic Variants of Butyrylcholinesterase and Their Potential Impact on Human Health

Butyrylcholinesterase (BChE) is an enzyme found in plasma and many other parts of the body. It is enzyme that hydrolyses drugs containing ester bonds such as drugs acting at the neuromuscular junction (succinylcholine) and local anaesthetics (procaine). Examination of the gene for mutations or polymorphisms causing the observed biochemical phenotypes has isolated those responsible for all the most widely known variants. The molecular bases of several genetic variants of BChE have been reported, such as the Atypical variant, fluoride-resistant variant, silent variant, K variant, J variant and C5 variant. In general, BChE polymorphisms have been shown to produce enzymes with varying levels of catalytic activity. Genetic variants of human butyrylcholinesterase were one of the first examples in the new field of pharmacogenetics when it was recognized that abnormal response to the succinylcholine was due to a mutated enzyme with low binding affinity. Beside that, variant of BChE has potential impact for Alzheimer disease patology

Timing of blood sampling for butyrylcholinesterase phenotyping in patients with prolonged neuromuscular block after mivacurium or suxamethonium.

Variants of butyrylcholinesterase are frequently associated with prolonged response to suxamethonium or mivacurium. Butyrylcholinesterase (BChE) can be characterized by phenotyping and determination of genotype. Inappropriate timing of blood sampling might interfere with phenotyping methods. However, guidelines regarding delay between exposure to anaesthesia and testing are not clearly defined. In this study, the BChE activity and phenotype in an early (T1) and late (T2) phase were compared and the phenotype/genotype correlation was assessed. Patients with a prolonged paralysis after mivacurium or suxamethonium were selected after ethical committee approval and written consent. BChE activity was based on butyrylthiocholine hydrolysis rate and phenotyping on differential inhibition of BChE activity with dibucaine and fluoride. DNA sequencing allowed genotypic characterization. We included the results of 20 patients with prolonged neuromuscular block (NMB) induced by mivacurium or suxamethonium. In these patients, BChE activity was different at T1 and T2 (2120 [1506-2733] UL-1 and 4055 [2810-5301] UL-1 , respectively; P=0.0014; values are mean [95% CI]). When phenotyping was possible, phenotyping at T1 and T2 yielded identical results. Phenotyping failed to identify one new variant (p.Tyr146Cys) and the K variant in 14 of 16 patients. Anaesthesia interfered with BChE activity, but not with phenotyping. Phenotyping can be performed on blood drawn during or immediately after recovery of mivacurium or suxamethonium to screen for clinically relevant variants of BChE. However, accurate diagnosis of BChE deficiency needs further confirmation by determination of genotype.

Genetic Testing for BCHE Variants Identifies Patients at Risk of Prolonged Neuromuscular Blockade in Response to Succinylcholine.

BackgroundGenetic variants in the BCHE (butyrylcholinesterase) gene are associated with reduced BChE enzyme activity and prolonged post-succinylcholine neuromuscular blockade, which can lead to postanesthetic apnea and respiratory depression. Testing for BChE deficiency is usually performed by biochemical methods and is generally only offered to patients who have a personal or family history of prolonged post-succinylcholine neuromuscular blockade.PurposeUsing a clinical test, we investigated the frequencies of BCHE genotypes that are associated with increased risk for prolonged post-succinylcholine neuromuscular blockade.Materials and MethodsFive BCHE variants, including the A (atypical, rs1799807), K (Kalow, rs1803274), F1 (fluoride-1, rs28933389), F2 (fluoride-2, rs28933390), and S1 (silent-1, rs398124632), were genotyped in a large (n = 13,301), multi-ethnic cohort in the United States. Subjects were recipients of pharmacogenetic testing ordered by their physicians as part of routine care.ResultsThe minor allele frequencies of A, K, F1, F2, and S1 were 1.60%, 19.93%, 0.08%, 0.47%, and 0.04%, respectively, in this cohort. Based on a review of biochemical and clinical data of these variants, we grouped BCHE genotypes into four phenotypic categories to stratify the risk for prolonged post-succinylcholine neuromuscular blockade. Approximately 0.06% of patients were predicted to have severe BChE deficiency, 8% were predicted to have moderate BChE deficiency, and 29% were predicted to have mild BChE deficiency. Compared to other ethnic groups, Caucasians were predicted to have the highest frequency of BChE deficiency.ConclusionWhile severe BChE deficiency is rare in the United States, approximately 8% of Americans are at moderate risk of prolonged post-succinylcholine neuromuscular blockade, suggesting that a sizable percentage of patients may benefit from preoperative genetic testing of BCHE.

The Preferable Binding Pose of Canonical Butyrylcholinesterase Substrates Is Unproductive for Echothiophate

In this paper, we, for the first time, describe the interaction between the butyrylcholinesterase enzyme and echothiophate, a popular model compound and an analogue of the chemical warfare agents VX and VR, at the atomistic level. Competition between the two echothiophate conformations in the active site was found using molecular modeling techniques. The first one is close to the mode of binding of the substrates of choline series (butyrylcholine and butyrylthiocholine) and is inhibitory, since it is unable to react with the enzyme. The second one is characterized by a significantly worse estimated binding affinity and is reactive. Thus, echothiophate combines the features of two types of inhibitors: competitive and suicidal. This observation will help clarify the kinetic reaction scheme in order to accurately assess the kinetic constants, which is especially important when designing new butyrylcholinesterase variants capable of full-cycle hydrolysis of organophosphorus compounds.

QM/MM Description of Newly Selected Catalytic Bioscavengers Against Organophosphorus Compounds Revealed Reactivation Stimulus Mediated by Histidine Residue in the Acyl-Binding Loop.

Butyrylcholinesterase (BChE) is considered as an efficient stoichiometric antidote against organophosphorus (OP) poisons. Recently we utilized combination of calculations and ultrahigh-throughput screening (uHTS) to select BChE variants capable of catalytic destruction of OP pesticide paraoxon. The purpose of this study was to elucidate the molecular mechanism underlying enzymatic hydrolysis of paraoxon by BChE variants using hybrid quantum mechanical/molecular mechanical (QM/MM) calculations. Detailed analysis of accomplished QM/MM runs revealed that histidine residues introduced into the acyl-binding loop are always located in close proximity with aspartate residue at position 70. Histidine residue acts as general base thus leading to attacking water molecule activation and subsequent SN2 inline hydrolysis resulting in BChE reactivation. This combination resembles canonical catalytic triad found in active centers of various proteases. Carboxyl group activates histidine residue by altering its pKa, which in turn promotes the activation of water molecule in terms of its nucleophilicity. Observed re-protonation of catalytic serine residue at position 198 from histidine residue at position 438 recovers initial configuration of the enzyme’s active center, facilitating next catalytic cycle. We therefore suggest that utilization of uHTS platform in combination with deciphering of molecular mechanisms by QM/MM calculations may significantly improve our knowledge of enzyme function, propose new strategies for enzyme design and open new horizons in generation of catalytic bioscavengers against OP poisons.

Bacterial Expression of Human Butyrylcholinesterase as a Tool for Nerve Agent Bioscavengers Development.

Human butyrylcholinesterase is a performant stoichiometric bioscavenger of organophosphorous nerve agents. It is either isolated from outdated plasma or functionally expressed in eukaryotic systems. Here, we report the production of active human butyrylcholinesterase in a prokaryotic system after optimization of the primary sequence through the Protein Repair One Stop Shop process, a structure- and sequence-based algorithm for soluble bacterial expression of difficult eukaryotic proteins. The mutant enzyme was purified to homogeneity. Its kinetic parameters with substrate are similar to the endogenous human butyrylcholinesterase or recombinants produced in eukaryotic systems. The isolated protein was prone to crystallize and its 2.5-Å X-ray structure revealed an active site gorge region identical to that of previously solved structures. The advantages of this alternate expression system, particularly for the generation of butyrylcholinesterase variants with nerve agent hydrolysis activity, are discussed.

Plant-expressed cocaine hydrolase variants of butyrylcholinesterase exhibit altered allosteric effects of cholinesterase activity and increased inhibitor sensitivity

Butyrylcholinesterase (BChE) is an enzyme with broad substrate and ligand specificities and may function as a generalized bioscavenger by binding and/or hydrolyzing various xenobiotic agents and toxicants, many of which target the central and peripheral nervous systems. Variants of BChE were rationally designed to increase the enzyme’s ability to hydrolyze the psychoactive enantiomer of cocaine. These variants were cloned, and then expressed using the magnICON transient expression system in plants and their enzymatic properties were investigated. In particular, we explored the effects that these site-directed mutations have over the enzyme kinetics with various substrates of BChE. We further compared the affinity of various anticholinesterases including organophosphorous nerve agents and pesticides toward these BChE variants relative to the wild type enzyme. In addition to serving as a therapy for cocaine addiction-related diseases, enhanced bioscavenging against other harmful agents could add to the practicality and versatility of the plant-derived recombinant enzyme as a multivalent therapeutic.

The C5 Variant of the Butyrylcholinesterase Tetramer Includes a Noncovalently Bound 60 kDa Lamellipodin Fragment.

Humans with the C5 genetic variant of butyrylcholinesterase (BChE) have 30–200% higher plasma BChE activity, low body weight, and shorter duration of action of the muscle relaxant succinylcholine. The C5 variant has an extra, slow-moving band of BChE activity on native polyacrylamide gel electrophoresis. This band is about 60 kDa larger than wild-type BChE. Umbilical cord BChE in 100% of newborn babies has a C5-like band. Our goal was to identify the unknown, 60 kDa protein in C5. Both wild-type and C5 BChE are under the genetic control of two independent loci, the BCHE gene on Chr 3q26.1 and the RAPH1 (lamellipodin) gene on Chr 2q33. Wild-type BChE tetramers are assembled around a 3 kDa polyproline peptide from lamellipodin. Western blot of boiled C5 and cord BChE showed a positive response with an antibody to the C-terminus of lamellipodin. The C-terminal exon of lamellipodin is about 60 kDa including an N-terminal polyproline. We propose that the unknown protein in C5 and cord BChE is encoded by the last exon of the RAPH1 gene. In 90% of the population, the 60 kDa fragment is shortened to 3 kDa during maturation to adulthood, leaving only 10% of adults with C5 BChE.

Butyrylcholinesterase K and Apolipoprotein E-ɛ4 Reduce the Age of Onset of Alzheimer's Disease, Accelerate Cognitive Decline, and Modulate Donepezil Response in Mild Cognitively Impaired Subjects.

Genetic heterogeneity in amnestic mild cognitively impaired (aMCI) subjects could lead to variations in progression rates and response to cholinomimetic agents. Together with the apolipoprotein E4 (APOE-ɛ4) gene, butyrylcholinesterase (BCHE) has become recently one of the few Alzheimer's disease (AD) susceptibility genes with distinct pharmacogenomic properties. To validate candidate genes (APOE/BCHE) which display associations with age of onset of AD and donepezil efficacy in aMCI subjects. Using the Petersen et al. (2005) study on vitamin E and donepezil efficacy in aMCI, we contrasted the effects of BCHE and APOE variants on donepezil drug response using the Alzheimer's Disease Assessment Score-Cognition (ADAS-Cog) scale. Independently, we assessed the effects of APOE/BCHE genotypes on age of onset and cortical choline acetyltransferase activity in autopsy-confirmed AD and age-matched control subjects. Statistical analyses revealed a significant earlier age of onset in AD for APOE-ɛ4, BCHE-K*, and APOE-ɛ4/BCHE-K* carriers. Among the carriers of APOE-ɛ4 and BCHE-K*, the benefit of donepezil was evident at the end of the three-year follow-up. The responder's pharmacogenomic profile is consistent with reduced brain cholinergic activity measured in APOE-ɛ4 and BCHE-K* positive subjects. APOE-ɛ4 and BCHE-K* positive subjects display an earlier age of onset of AD, an accelerated cognitive decline and a greater cognitive benefits to donepezil therapy. These results clearly emphasize the necessity of monitoring potential pharmacogenomic effects in this population of subjects, and suggest enrichment strategies for secondary prevention trials involving prodromal AD subjects.

Naturally Occurring Genetic Variants of Human Acetylcholinesterase and Butyrylcholinesterase and Their Potential Impact on the Risk of Toxicity from Cholinesterase Inhibitors.

Acetylcholinesterase (AChE) is the physiologically important target for organophosphorus toxicants (OP) including nerve agents and pesticides. Butyrylcholinesterase (BChE) in blood serves as a bioscavenger that protects AChE in nerve synapses from inhibition by OP. Mass spectrometry methods can detect exposure to OP by measuring adducts on the active site serine of plasma BChE. Genetic variants of human AChE and BChE do exist, but loss of function mutations have been identified only in the BCHE gene. The most common AChE variant, His353Asn (H322N), also known as the Yt blood group antigen, has normal AChE activity. The most common BChE variant, Ala567Thr (A539T) or the K-variant in honor of Werner Kalow, has 33% reduced plasma BChE activity. The genetic variant most frequently associated with prolonged response to muscle relaxants, Asp98Gly (D70G) or atypical BChE, has reduced activity and reduced enzyme concentration. Early studies in young, healthy males, performed at a time when it was legal to test nerve agents in humans, showed that individuals responded differently to the same low dose of sarin with toxic symptoms ranging in severity from minimal to moderate. Additionally, animal studies indicated that BChE protects from toxicants that have a higher reactivity with AChE than with BChE (e.g., nerve agents) but not from toxicants that have a higher reactivity with BChE than with AChE (e.g., OP pesticides). As a corollary, we hypothesize that individuals with genetic variants of BChE may be at increased risk of toxicity from nerve agents but not from OP pesticides.

Understanding the non-catalytic behavior of human butyrylcholinesterase silent variants: Comparison of wild-type enzyme, catalytically active Ala328Cys mutant, and silent Ala328Asp variant

Conformational dynamics of wild-type human butyrylcholinesterase (BChE), two mutants of residue Ala328, the catalytically active Ala328Cys, and the catalytically inactive (silent) Ala328Asp, and their interactions with butyrylcholine were studied. The aim was to understand the molecular mechanisms by which point mutations may lead to silent BChE variant or alter catalytic activity. Importance of BChE natural variants is due to medical consequences, i.e. prolonged apnea, following administration of the myorelaxant esters, succinylcholine and mivacurium.Comparison of molecular dynamics (MD) simulations for the three model systems showed that: 1) the active mutant Ala328Cys mutant has some changes in configuration of catalytic residues, which do not prevent binding of butyrylcholine to the active site; 2) in the naturally-occurring silent variant Ala328Asp, the Asp328 carboxylate may either form a salt bridge with Lys339 or a H-bond with His438. In the first case, the Ω-loop swings off the gorge, disrupting the π-cation binding site and the catalytic triad. In the second case, binding of cationic substrates in the catalytic center is also impaired. MD simulations carried out in 0.15 M NaCl, close to physiological ionic strength conditions, favored the second situation. It was seen that Asp328 forms a H-bond with the catalytic triad His438, which in turn disrupts the catalytic machinery. Therefore, we concluded that the Ala328Asp variant is not catalytically active because of that dramatic event. Computational results, consistent with in vitro biochemical data and clinical observations, validate our MD approach.

Predictors of the variability in neuromuscular block duration following succinylcholine: A prospective, observational study.

The duration of neuromuscular block (NMB) following succinylcholine administration is characterised by a high interindividual variability. However, this has not yet been quantified in a large sample of surgical patients. The significance of underlying clinical factors is unknown. The objective of this study was to profile the variability in NMB duration following a standard dose of succinylcholine and to investigate contributing clinical and genetic factors. A prospective, observational study. Tertiary referral centre. In a total of 1630 surgical patients undergoing a rapid sequence induction and intubation, clinical risk factors for a prolongation in NMB duration following succinylcholine were assessed. In a subset of 202 patients, additional biochemical and molecular genetic investigations of butyrylcholinesterase were performed. A standard 1 mg kg dose of succinylcholine after administration of an induction drug and an opioid. NMB duration measured as the time between administration of succinylcholine until reappearance of palpable muscular response to supramaximal transcutaneous ulnar nerve stimulation. NMB varied from 80 s to 44 min with a median duration of 7.3 min. Sixteen percent of patients had NMB duration in excess of 10 min. A multivariable survival model identified physical status, sex, age, hepatic disease, pregnancy, history of cancer and use of etomidate or metoclopramide as independent risk factors for a prolonged NMB. Three novel butyrylcholinesterase variants were identified: p.Ile5Thr; p.Val178Ile; and p.Try231Ser. Neuromuscular blockade duration in excess of 10 min occurred in 16% of a general surgical population following a single dose of succinylcholine. The multivariable model of clinical risk factors for prolonged NMB revealed a negative predictive value of 87%, thereby indicating that absence of such risk factors may reliably predict a shorter duration of NMB. In patients with clinical risk factors for a prolonged NMB or with butyrylcholinesterase mutations, an alternative to succinylcholine should be considered.

The allele frequency of T920C mutation in butyrylcholinesterase gene is high in an Indian population

The genetic variants of butyrylcholinesterase (BChE) are the cause of concern in individuals experiencing prolonged apnea on administration of muscle relaxants. In an Indian community called Vysya, a variant (L307P; T920C) was associated with imperceptible plasma BChE. Since BChE has several pharmacological significances in humans, the identification of its variants having altered activity is very important. Previous studies for identifying the mutants in a population were based only on its functional attributes (phenotypic characters) such as esterase activity, dibucaine number and fluoride number. Generally phenotyping method is not considered as the accurate methodology till date though it might be used as a primary screening tool. Molecular biology provides a better technique in identifying these variants. Our aim was to screen this particular community living in South India for the heterozygosity of T920C mutation by phenotypic and genotypic analysis and to find the reliability between the two methods. We analysed 266 individuals for the heterozygosity of T920C. Based on BChE phenotypes, we found that 95% of the individuals are heterozygous. Real-time PCR based genotyping revealed that 96% of individuals are heterozygous. The allele frequency for the mutant allele C was 0.52 which confirmed that the genetic pool of this allele is much higher in Vysya. Also, we observed that genotyping correlates 97% with the phenotype in our study. Further, both phenotype and genotype of age matched other ethnic group do not show any preponderance to this mutation authenticating the vulnerability of Vysyas to this mutation is dominant.

Effect of Rivastigmine or Memantine Add-on Therapy Is Affected by Butyrylcholinesterase Genotype in Patients with Probable Alzheimer's Disease

Background: The K variant of butyrylcholinesterase (BCHE-K) exhibits a reduced acetylcholine-hydrolyzing capacity; so the clinical response to rivastigmine may differ in Alzheimer's disease (AD) patients with the BCHE-K gene. Objective: To investigate the clinical response to rivastigmine transdermal patch monotherapy or memantine plus rivastigmine transdermal patch therapy in AD patients based on the BCHE-K gene. Methods: A total of 146 probable AD patients consented to genetic testing for butyrylcholinesterase and underwent the final efficacy evaluations. Responders were defined as patients with an equal or better score on the Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog) at 16 weeks compared to their baseline score. Results:BCHE-K carriers showed a lower responder rate on the ADAS-cog than non-carriers (38.2 vs. 61.7%, p = 0.02), and this trend was evident in AD patients with apolipoprotein E I 4 (35 vs. 60.7%, p = 0.001). The presence of the BCHE-K allele predicted a worse response on the ADAS-cog (odds ratio 0.35, 95% confidence interval 0.14-0.87), after adjusting for demographic and baseline cognitive and functional variables. Conclusion: The BCHE-K genotype may be related to a poor cognitive response to rivastigmine patch or memantine add-on therapy, especially in the presence of apolipoprotein E I 4. i 2014 S. Karger AG, Basel

Genotyping single-nucleotide polymorphisms of human genes involved in organophosphate detoxification by high-resolution melting

Paraoxonase-1 (PON1) and butyrylcholinesterase (BCHE) are natural bioscavengers of organophosphate acetylcholinesterase inhibitors in the human body, which can determine individual sensitivity to organophosphate toxicity. Interindividual differences in activity of PON1 (catalytic bioscavenger) and substrate specificity are strongly associated with the substitution of two amino acids: Leu/Met (L/M) at position 55 (rs854560) and Gln/Arg (Q/R) at position 192 (rs662). In the case of BCHE (stoichiometric bioscavenger) substitution, Ala/Thr (A/T) at position 539 produces the so-called "K-variant" of the enzyme (rs1803274). Threonine allele is often co-inherited with an atypical BCHE allele (rs1799807). The atypical variant of BCHE displays a lower affinity for cholinesterase inhibitors. Genotyping rs662 and rs1803274 single-nucleotide polymorphisms (SNP) by high-resolution melting (HRM) is facilitated by the nucleotide substitution A>G (G>A), which resulted in a changed number of hydrogen bonds in the PCR product and, consequently, shifted T m. In the case of rs854560, genotyping is complicated by the nucleotide substitution T>A, which has no significant effect on the T m of the PCR product. An addition of a small quantity of LL homozygote DNA into the reaction mixture before PCR discriminates the three genotypes by the melt curves due to different amounts of heteroduplexes formed in the LM and MM samples. HRM analysis can be applied for genotyping human rs854560, rs662, and rs1803274 SNPs.

An Indian butyrylcholinesterase variant L307P is not structurally stable: A molecular dynamics simulation study

The human butyrylcholinesterase (BChE) activity is less than 1% in the serum of silent variant individuals of Vysya community in India. They are homozygous for a point mutation at codon 307 (CTT→CCT) resulting in the substitution of leucine 307 by proline. The reason for the disappearance of the protein in the serum has not been explicated till date. Based on this background, we performed molecular dynamics simulation to probe the structural stability of Indian variant (L307P) in comparison with wild and other BChE variants (D70G, E497V, V142M) having differential esterase activity. The simulation of all the mutants except D70G showed a much larger Cα root mean square deviation from the wild BChE crystal structure, showing the overall conformational disturbance. Further analysis revealed that secondary structure of the mutant proteins was not stable. The orientation of the catalytic triad is also distorted in all the mutants. The distance between δ nitrogen of His438 to ε oxygen of Glu325 and ε nitrogen of His438 to γ oxygen of Ser198 were highly altered in L307P mutant than the wild and other three variants throughout the simulation. Such disparity of distances between the catalytic residues may be due to the change in the protein conformation attributing to their differential catalytic activity. Our studies thus prove that the Indian BChE L307P mutant with negligible activity is possibly due to its structural instability when compared to other BChE variants.

Association analysis between K and −116A variants of butyrylcholinesterase and Alzheimer’s disease in a Brazilian population

In Alzheimer’s disease (AD) a reduction in acetylcholinesterase (AChE) and an increase in butyrylcholinesterase (BChE) activity are observed. K variant (539T) is the most common variant of the BCHE gene and, although controversial, several studies reported association between K variant and AD. Previous results showed that the K variant alone is not capable of diminishing BChE activity, depending on the presence of the −116A variant. Considering that, we conducted a case-control association study using a clinically well defined group of AD patients (n=82) and age and sex matched control subjects (EC; n=78) in order to test the association with these variations of BCHE gene in a Brazilian population. The allele, genotype and haplotype frequencies of the K and the −116A variants of BCHE gene were not significantly different between cases and controls. Although not reaching statistical significance, the results suggested that the presence of −116A variant may have a protective effect against AD. The association of the K variant with AD in a controversial manner in different surveys is probably caused by its linkage disequilibrium with −116A that, by reducing BChE activity, potentially increases cholinergic transmission in comparison with usual genotypes.