From monomer to fibril: Abeta-amyloid binding to Aducanumab antibody studied by molecular dynamics simulation

Alzheimer's disease is one of the most common causes of dementia. It is believed that the aggregation of short Aβ -peptides to form oligomeric and protofibrillar amyloid assemblies plays a central role for disease-relevant neurotoxicity. In recent years, passive immunotherapy has been introduced as a potential treatment strategy with anti-amyloid antibodies binding to Aβ -amyloids and inducing their subsequent degradation by the immune system. Although so far mostly unsuccessful in clinical studies, the high-dosed application of the monoclonal antibody Aducanumab has shown therapeutic potential that might be attributed to its much greater affinity to Aβ -aggregates vs monomeric Aβ -peptides. In order to better understand how Aducanumab interacts with aggregated Aβ -forms compared to monomers, we have generated structural model complexes based on the known structure of Aducanumab in complex with an Aβ_{2 − 7} -eptitope. Structural models of Aducanumab bound to full-sequence Aβ_{1 − 40} -monomers, oligomers, protofilaments and mature fibrils were generated and investigated using extensive molecular dynamics simulations to characterize the flexibility and possible additional interactions. Indeed, an aggregate-specific N-terminal binding motif was found in case of Aducanumab binding to oligomers, protofilaments and fibrils that is located next to but not overlapping with the epitope binding site found in the crystal structure with Aβ_{2 − 7} . Analysis of binding energetics indicates that this motif binds weaker than the epitope but likely contributes to Aducanumab's preference for aggregated Aβ -species. The predicted aggregate-specific binding motif could potentially serve as a basis to reengineer Aducanumab for further enhanced preference to bind Aβ -aggregates vs monomers.     

Functional characterization of human myosin-binding protein C3 variants associated with hypertrophic cardiomyopathy reveals exon-specific cardiac phenotypes in zebrafish model

Myosin-binding protein C 3 (MYBPC3) variants are the most common cause of hypertrophic cardiomyopathy (HCM). HCM is a complex cardiac disorder due to its significant genetic and clinical heterogeneity. MYBPC3 variants genotype–phenotype associations remain poorly understood. We investigated the impact of two novel human MYBPC3 splice-site variants: V1: c.654+2_654+4dupTGG targeting exon 5 using morpholino MOe5i5; and V2: c.772+1G>A targeting exon 6 using MOe6i6; located within C1 domain of cMyBP-C protein, known to be critical in regulating sarcomere structure and contractility. Zebrafish MOe5i5 and MOe6i6 morphants recapitulated typical characteristics of human HCM with cardiac phenotypes of varying severity, including reduced cardiomyocyte count, thickened ventricular myocardial wall, a drastic reduction in heart rate, stroke volume, and cardiac output. Analysis of all cardiac morphological and functional parameters demonstrated that V2 cardiac phenotype was more severe than V1. Coinjection with synthetic human MYBPC3 messenger RNA (mRNA) partially rescued disparate cardiac phenotypes in each zebrafish morphant. While human MYBPC3 mRNA partially restored the decreased heart rate in V1 morphants and displayed increased percentages of ejection fraction, fractional shortening, and area change, it failed to revert the V1 ventricular myocardial thickness. These results suggest a possible V1 impact on cardiac contractility. In contrast, attempts to rescue V2 morphants only restored the ventricular myocardial wall hypertrophy phenotype but had no significant effect on impaired heart rate, suggesting a potential V2 impact on the cardiac structure. Our study provides evidence of an association between MYBPC3 exon-specific cardiac phenotypes in the zebrafish model providing important insights into how these genetic variants contribute to HCM disease.     

The polymorphism in the promoter region of metallothionein 1 is associated with heat tolerance of scallop Argopecten irradians

Metallothioneins (MTs), a superfamily of cysteine-rich proteins, perform multiple functions, such as maintaining homeostasis of essential metals, detoxification of toxic metals and scavenging of oxyradicals. In this study, the promoter region of a metallothionein (MT) gene from Bay scallop Argopecten irradians (designed as AiMT1) was cloned by the technique of genomic DNA walking, and the polymorphisms in this region were screened to find their association with susceptibility or tolerance to high temperature stress. One insert–deletion (ins–del) polymorphism and sixteen single nucleotide polymorphisms (SNPs) were identified in the amplified promoter region. Two SNPs, − 375 T–C and − 337 A–C, were selected to analyze their distribution in the two Bay scallop populations collected from southern and northern China coast, which were identified as heat resistant and heat susceptible stocks, respectively. There were three genotypes, T/T, T/C and C/C, at locus − 375, and their frequencies were 25%, 61.1% and 13.9% in the heat susceptible stock, while 34.2%, 42.1% and 23.7% in the resistant stock, respectively. There was no significant difference in the frequency distribution of different genotypes between the two stocks (P > 0.05). In contrast, at locus − 337, three genotypes A/A, A/C and C/C were revealed with the frequencies of 11.6%, 34.9% and 53.5% in the heat susceptible stock, while 45.7%, 32.6% and 21.7% in the heat resistant stock, respectively. The frequency of C/C genotype in the heat susceptible stock was significantly higher (P < 0.01) than that in the heat resistant stock, while the frequency of A/A in the heat resistant stock was significantly higher (P < 0.01) than that in the heat susceptible stock. Furthermore, the expression of AiMT1 mRNA in scallops with C/C genotype was significantly higher than that with A/A genotype (P < 0.05) after an acute heat treatment at 28 °C for 120 min. These results implied that the polymorphism at locus − 337 of AiMT1 was associated with the susceptibility/tolerance of scallops to heat stress, and the − 337 A/A genotype could be a potential marker available in future selection of Bay scallop with heat tolerance.     

Contribution of genetic and epigenetic mechanisms to Wnt pathway activity in prevalent skeletal disorders

We reported previously that the expression of Wnt-related genes is lower in osteoporotic hip fractures than in osteoarthritis. We aimed to confirm those results by analyzing β-catenin levels and explored potential genetic and epigenetic mechanisms involved.     

Identification of multiple binding sites for the THAP domain of the Galileo transposase in the long terminal inverted-repeats

Galileo is a DNA transposon responsible for the generation of several chromosomal inversions in Drosophila. In contrast to other members of the P-element superfamily, it has unusually long terminal inverted-repeats (TIRs) that resemble those of Foldback elements. To investigate the function of the long TIRs we derived consensus and ancestral sequences for the Galileo transposase in three species of Drosophilids. Following gene synthesis, we expressed and purified their constituent THAP domains and tested their binding activity towards the respective Galileo TIRs. DNase I footprinting located the most proximal DNA binding site about 70 bp from the transposon end. Using this sequence we identified further binding sites in the tandem repeats that are found within the long TIRs. This suggests that the synaptic complex between Galileo ends may be a complicated structure containing higher-order multimers of the transposase. We also attempted to reconstitute Galileo transposition in Drosophila embryos but no events were detected. Thus, although the limited numbers of Galileo copies in each genome were sufficient to provide functional consensus sequences for the THAP domains, they do not specify a fully active transposase. Since the THAP recognition sequence is short, and will occur many times in a large genome, it seems likely that the multiple binding sites within the long, internally repetitive, TIRs of Galileo and other Foldback-like elements may provide the transposase with its binding specificity.