Similarities and Differences within Members of the Ff Family of Filamentous Bacteriophage Viruses

Rapid discrimination of African swine fever virus nucleic acid and virions using BenzoNuclease

African swine fever (ASF) is an acute and severe infectious disease caused by the African Swine Fever Virus (ASFV). ASFV exhibits significant resistance and stability in the environment, which, coupled with its double-stranded DNA and large genome, predisposes it to contaminate laboratory samples. This characteristic can lead to false-positive results in swine farm settings even days after disinfection, as detectable through polymerase chain reaction (PCR) or real-time fluorescent quantitative PCR (qPCR) assays. To meet the demand for efficient clinical methods capable of discriminating between ASFV nucleic acid and ASFV virions, this study aims to ascertain the efficacy of the nuclease "BenzoNuclease" in distinguishing ASFV nucleic acid (ASFV-DNA) from ASFV virions. BenzoNuclease is a versatile nucleic acid enzyme with the capacity to degrade nearly all forms of DNA and RNA. Initially, this research established a highly sensitive general PCR detection method for ASFV. Subsequently, a positive control was constructed using the M13 bacteriophage to substitute for active ASFV, facilitating the development of an improved qPCR method. It is important to note that common disinfectants have the potential to deactivate BenzoNuclease. However, in an environment simulating actual production applications, residual disinfectants do not interfere with the enzymatic efficacy of BenzoNuclease, thus not affecting the detection capabilities of this method. Positive clinical samples from pig farms, upon testing with the improved method, revealed that three samples were positive, indicating the presence of viral particles, while the remaining samples were negative, indicating the presence of nucleic acids. This provides an additional new option for sample testing in pig farms.

Dynamics in the Intact fd Bacteriophage Revealed by Pseudo 3D REDOR-Based Magic Angle Spinning NMR

The development of robust NMR methodologies to probe dynamics on the atomic scale is vital to elucidate the close relations between structure, motion, and function in biological systems. Here, we present an automated protocol to measure, using magic-angle spinning NMR, the effective 13C-15N dipolar coupling constants between multiple spin pairs simultaneously with high accuracy. We use the experimental dipolar coupling constants to quantify the order parameters of multiple C-N bonds in the thousands of identical copies of the coat protein in intact fd-Y21M filamentous bacteriophage virus and describe its overall dynamics on the submillisecond time scale. The method is based on combining three pseudo three-dimensional NMR experiments, where a rotational echo double resonance (REDOR) dephasing block, designed to measure internuclear distances, is combined with three complementary 13C-13C mixing schemes: dipolar-assisted rotational resonance, through-bond transfer-based double quantum/single quantum correlation, and radio frequency driven recoupling. These mixing schemes result in highly resolved carbon spectra with correlations that are created by different transfer mechanisms. We show that the helical part of the coat protein undergoes a uniform small (∼30°) amplitude motion, while the N-terminus is highly flexible. In addition, our results suggest that the reduced mobility of lysine sidechains at the C-terminus are a signature of binding to the single stranded DNA.

Structure, Biology, and Applications of Filamentous Bacteriophages

The closely related Escherichia coli Ff filamentous phages (f1, fd, and M13) have taken a fantastic journey over the past 60 years, from the urban sewerage from which they were first isolated, to their use in high-end technologies in multiple fields. Their relatively small genome size, high titers, and the virions that tolerate fusion proteins make the Ffs an ideal system for phage display. Folding of the fusions in the oxidizing environment of the E. coli periplasm makes the Ff phages a platform that allows display of eukaryotic surface and secreted proteins, including antibodies. Resistance of the Ffs to a broad range of pH and detergents facilitates affinity screening in phage display, whereas the stability of the virions at ambient temperature makes them suitable for applications in material science and nanotechnology. Among filamentous phages, only the Ffs have been used in phage display technology, because of the most advanced state of knowledge about their biology and the various tools developed for E. coli as a cloning host for them. Filamentous phages have been thought to be a rather small group, infecting mostly Gram-negative bacteria. A recent discovery of more than 10 thousand diverse filamentous phages in bacteria and archaea, however, opens a fascinating prospect for novel applications. The main aim of this review is to give detailed biological and structural information to researchers embarking on phage display projects. The secondary aim is to discuss the yet-unresolved puzzles, as well as recent developments in filamentous phage biology, from a viewpoint of their impact on current and future applications.

Harnessing filamentous phages for enhanced stroke recovery

Stroke poses a critical global health challenge, leading to substantial morbidity and mortality. Existing treatments often miss vital timeframes and encounter limitations due to adverse effects, prompting the pursuit of innovative approaches to restore compromised brain function. This review explores the potential of filamentous phages in enhancing stroke recovery. Initially antimicrobial-centric, bacteriophage therapy has evolved into a regenerative solution. We explore the diverse role of filamentous phages in post-stroke neurological restoration, emphasizing their ability to integrate peptides into phage coat proteins, thereby facilitating recovery. Experimental evidence supports their efficacy in alleviating post-stroke complications, immune modulation, and tissue regeneration. However, rigorous clinical validation is essential to address challenges like dosing and administration routes. Additionally, genetic modification enhances their potential as injectable biomaterials for complex brain tissue issues. This review emphasizes innovative strategies and the capacity of filamentous phages to contribute to enhanced stroke recovery, as opposed to serving as standalone treatment, particularly in addressing stroke-induced brain tissue damage.

Engineered M13 phage as a novel therapeutic bionanomaterial for clinical applications: From tissue regeneration to cancer therapy

Bacteriophages (phages) are nanostructured viruses with highly selective antibacterial properties that have gained attention beyond eliminating bacteria. Specifically, M13 phages are filamentous phages that have recently been studied in various aspects of nanomedicine due to their biological advantages and more compliant engineering capabilities over other phages. Having nanofiber-like morphology, M13 phages can reach varied target sites and self-assemble into multidimensional scaffolds in a relatively safe and stable way. In addition, genetic modification of the coat proteins enables specific display of peptides and antibodies on the phages, allowing for precise and individualized medicine. M13 phages have also been subjected to novel engineering approaches, including phage-based bionanomaterial engineering and phage-directed nanomaterial combinations that enhance the bionanomaterial properties of M13 phages. In view of these features, researchers have been able to utilize M13 phages for therapeutic applications such as drug delivery, biodetection, tissue regeneration, and targeted cancer therapy. In particular, M13 phages have been utilized as a novel bionanomaterial for precisely mimicking natural tissue environment in order to overcome the shortage in tissue and organ donors. Hence, in this review, we address the recent studies and advances of using M13 phages in the field of nanomedicine as therapeutic agents based upon their characteristics as novel bionanomaterial with biomolecules displayed. This paper also emphasizes the novel engineering approach that enhances M13 phage's bionanomaterial capabilities. Current limitations and future approaches are also discussed to provide insight in further progress for M13 phage-based clinical applications.

Virus Structures and Dynamics by Magic-Angle Spinning NMR

Techniques for atomic-resolution structural biology have evolved during the past several decades. Breakthroughs in instrumentation, sample preparation, and data analysis that occurred in the past decade have enabled characterization of viruses with an unprecedented level of detail. Here we review the recent advances in magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy for structural analysis of viruses and viral assemblies. MAS NMR is a powerful method that yields information on 3D structures and dynamics in a broad range of experimental conditions. After a brief introduction, we discuss recent structural and functional studies of several viruses investigated with atomic resolution at various levels of structural organization, from individual domains of a membrane protein reconstituted into lipid bilayers to virus-like particles and intact viruses. We present examples of the unique information revealed by MAS NMR about drug binding, conduction mechanisms, interactions with cellular host factors, and DNA packaging in biologically relevant environments that are inaccessible by other methods.

Nonuniformly sampled exclusively-13 C/15 N 4D solid-state NMR experiments: Assignment and characterization of IKe phage capsid

An important step in the process of protein research by NMR is the assignment of chemical shifts. In the coat protein of IKe bacteriophage, there are 53 residues making up a long helix resulting in relatively high spectral ambiguity. Assignment thus requires the collection of a set of three-dimensional (3D) experiments and the preparation of sparsely labeled samples. Increasing the dimensionality can facilitate fast and reliable assignment of IKe and of larger proteins. Recent progress in nonuniform sampling techniques made the application of multidimensional NMR solid-state experiments beyond 3D more practical. 4D ¹ H-detected experiments have been demonstrated in high-fields and at spinning speeds of 60 kHz and higher but are not practical at spinning speeds of 10-20 kHz for fully protonated proteins. Here, we demonstrate the applicability of a nonuniformly sampled 4D ¹³ C/¹⁵ N-only correlation experiment performed at a moderate field of 14.1 T, which can incorporate sufficiently long acquisition periods in all dimensions. We show how a single CANCOCX experiment, supported by several 2D carbon-based correlation experiments, is utilized for the assignment of heteronuclei in the coat protein of the IKe bacteriophage. One sparsely labeled sample was used to validate sidechain assignment of several hydrophobic-residue sidechains. A comparison to solution NMR studies of isolated IKe coat proteins embedded in micelles points to key residues involved in structural rearrangement of the capsid upon assembly of the virus. The benefits of 4D to a quicker assignment are discussed, and the method may prove useful for studying proteins at relatively low fields.

Structural characterization of bacteriophage viruses by NMR

Magic-angle spinning (MAS) solid-state NMR has provided structural insights into various bacteriophage systems including filamentous, spherical, and tailed bacteriophage viruses. A variety of methodologies have been utilized including elementary two and three-dimensional assignment experiments, proton-detection techniques at fast spinning speeds, non-uniform sampling, structure determination protocols, conformational dynamics revealed by recoupling of anisotropic interactions, and enhancement by dynamic nuclear polarization. This review summarizes most of the studies performed during the last decade by MAS techniques and makes comparisons with prior knowledge obtained from static and solution NMR techniques. Chemical shifts for the capsids of the various systems are reported and analyzed, and DNA shifts are reported and discussed in the context of general high molecular-weight DNA molecules. Chemical shift and torsion angle prediction techniques are compared and applied to the various phage systems. The structures of the intact M13 filamentous bacteriophage and that of the Acinetobacter phage AP205 capsid, determined using MAS-based experimental data, are presented. Finally, filamentous phages, which are highly rigid systems, show interesting dynamics at the interface of the capsid and DNA, and their mutual electrostatic interactions are shown to be mediated by highly mobile positively charged residues. Novel results obtained from recoupling the chemical shift anisotropy of a single arginine in IKe phage, which is in contact with its DNA, further demonstrate this point. MAS NMR thus provides many new insights into phage structure, and on the other hand the richness, complexity and variety of bacteriophage systems provide opportunities for new NMR methodologies and technique developments.

A Protofilament-Protofilament Interface in the Structure of Mouse α-Synuclein Fibrils

Fibrillar α-synuclein (AS) is the major component of Lewy bodies, the pathological hallmark of Parkinson's disease. Using solid-state nuclear magnetic resonance (ssNMR), we previously reported a structural characterization of mouse AS (mAS) fibrils and found that the secondary structure of the mAS fibrils is highly similar to a form of human AS (hAS) fibrils. Recently, a three-dimensional structure of these same hAS fibrils was determined by ssNMR and scanning transmission electron microscopy. Using medium- and long-range distance restraints obtained from ssNMR spectra, we found that the single protofilament structure of mAS fibrils is also similar to that of the hAS fibrils. However, residue-specific water accessibility of mAS fibrils probed by water polarization transfer ssNMR measurements indicates that residues S42-T44 and G84-V95 are largely protected from water even though they are located at the edge of the protofilament. Some of the corresponding resonances also exhibit peak doubling. These observations suggest that these residues may be involved in, to our knowledge, a novel protofilament-protofilament interface. We propose a structural model of mAS fibrils that incorporates this dimer interface.

Dynamic Nuclear Polarization Magic-Angle Spinning Nuclear Magnetic Resonance Combined with Molecular Dynamics Simulations Permits Detection of Order and Disorder in Viral Assemblies

We report dynamic nuclear polarization (DNP)-enhanced magic-angle spinning (MAS) NMR spectroscopy in viral capsids from HIV-1 and bacteriophage AP205. Viruses regulate their life cycles and infectivity through modulation of their structures and dynamics. While static structures of capsids from several viruses are now accessible with near-atomic-level resolution, atomic-level understanding of functionally important motions in assembled capsids is lacking. We observed up to 64-fold signal enhancements by DNP, which permitted in-depth analysis of these assemblies. For the HIV-1 CA assemblies, a remarkably high spectral resolution in the 3D and 2D heteronuclear data sets permitted the assignment of a significant fraction of backbone and side-chain resonances. Using an integrated DNP MAS NMR and molecular dynamics (MD) simulation approach, the conformational space sampled by the assembled capsid at cryogenic temperatures was mapped. Qualitatively, a remarkable agreement was observed for the experimental ¹³C/¹⁵N chemical shift distributions and those calculated from substructures along the MD trajectory. Residues that are mobile at physiological temperatures are frozen out in multiple conformers at cryogenic conditions, resulting in broad experimental and calculated chemical shift distributions. Overall, our results suggest that DNP MAS NMR measurements in combination with MD simulations facilitate a thorough understanding of the dynamic signatures of viral capsids.

Rapid automated determination of chemical shift anisotropy values in the carbonyl and carboxyl groups of fd-y21m bacteriophage using solid state NMR

Determination of chemical shift anisotropy (CSA) in immobilized proteins and protein assemblies is one of several tools to determine protein dynamics on the timescales of microseconds and faster. The large CSA values of C=O groups in the rigid limit makes them in particular attractive for measurements of large amplitude motions, or their absence. In this study, we implement a 3D R-symmetry-based sequence that recouples the second spatial component of the ¹³C CSA with the corresponding isotropic ¹³C'-¹³C cross-peaks in order to probe backbone and sidechain dynamics in an intact fd-y21m filamentous phage viral capsid. The assignment of the isotropic cross-peaks and the analysis were conducted automatically using a new software named 'Raven'. The software can be utilized to auto-assign any 2D ¹³C-¹³C or ¹⁵N-¹³C spectrum given a previously-determined assignment table and generates simultaneously all intensity curves acquired in the third dimension. Here, all CSA spectra were automatically generated, and subsequently matched against a simulated set of CSA curves to yield their values. For the multi-copy, 50-residue-long protein capsid of fd-y21m, the backbone of the helical region is rigid, with reduced CSA values of ~ 12.5 kHz (~ 83 ppm). The N-terminus shows motionally-averaged CSA lineshapes and the carboxylic sidechain groups of four residues indicate large amplitude motions for D4, D5, D12 and E20. The current results further strengthen our previous studies of ¹⁵N CSA values and are in agreement with qualitative analysis of ¹³C-¹³C dipolar build-up curves, which were automatically obtained using our software. Our automated analysis technique is general and can be applied to study protein structure and dynamics, with data resulting from experiments that probe different variables such as relaxation rates and scaled anisotropic interactions.

Mutation of M13 Bacteriophage Major Coat Protein for Increased Conjugation to Exogenous Compounds

Over the past ten years there has been increasing interest in the conjugation of exogenous compounds to the surface of the M13 bacteriophage. M13 offers a convenient scaffold for the development of nanoassemblies with useful functions, such as highly specific drug delivery and pathogen detection. However, the progress of these technologies has been hindered by the limited efficiency of conjugation to the bacteriophage. Here we generate a mutant version of M13 with an additional lysine residue expressed on the outer surface of the M13 major coat protein, pVIII. We show that this mutation is accommodated by the bacteriophage and that up to an additional 520 exogenous groups can be attached to the bacteriophage surface via amine-directed conjugation. These results could aid the development of high payload drug delivery nanoassemblies and pathogen detection systems with increased sensitivity.

Filamentous Bacteriophage Viruses: Preparation, Magic-Angle Spinning Solid-State NMR Experiments, and Structure Determination

Filamentous bacteriophages are elongated semi-flexible viruses that infect bacteria. They consist of a circular single-stranded DNA (ssDNA) wrapped by a capsid consisting of thousands of copies of a major coat protein subunit. Given the increasing number of discovered phages and the existence of only a handful of structures, the development of methods for phage structure determination is valuable for biophysics and structural virology. In recent years, we developed and applied techniques to elucidate the 3D atomic-resolution structures of intact bacteriophages using experimental magic-angle spinning (MAS) solid-state NMR data. The flexibility in sample preparation - precipitated homogeneous solids - and the fact that ssNMR presents no limitation on the size, weight or morphology of the system under study makes it an ideal approach to study phage systems in detail.In this contribution, we describe approaches to prepare isotopically carbon-13 and nitrogen-15 enriched intact phage samples in high yield and purity, and we present experimental MAS NMR methods to study the capsid secondary and tertiary structure, and the DNA-capsid interface. Protocols for the capsid structure determination using the Rosetta modeling software are provided. Specific examples are given from studies of the M13 and fd filamentous bacteriophage viruses.

Structural Effects of Single Mutations in a Filamentous Viral Capsid Across Multiple Length Scales

Filamentous bacteriophage (phage) are single-stranded DNA viruses that infect bacteria. Single-site mutants of fd phage have been studied by magic-angle spinning nuclear magnetic resonance and by small-angle X-ray scattering. Detailed analysis has been performed that provides insight into structural variations on three length scales. The results, analyzed in conjunction with existing literature data, suggest that a single charge mutation on the capsid surface affects direct interviral interactions but not the structure of individual particles or the macroscale organization. On the other hand, a single hydrophobic mutation located at the hydrophobic interface that stabilizes capsid assembly alters the atomic structure of the phage, mainly affecting intersubunit interactions, affects its macroscale organization, that is, the pitch of the cholesteric liquid crystal formed by the particles, but skips the nanoscale hence does not affect direct interparticle interactions. An X-ray scattering under osmotic pressure assay provides the effective linear charge density of the phage and we obtain values of 0.6 Å^-1 and 0.4 Å^-1 for fd and M13 phage, respectively. These values agree with a simple consideration of a single cylinder with protein and DNA charges spread according to the most recent atomic-resolution models of the phage.

Structural biology of supramolecular assemblies by magic-angle spinning NMR spectroscopy

In recent years, exciting developments in instrument technology and experimental methodology have advanced the field of magic-angle spinning (MAS) nuclear magnetic resonance (NMR) to new heights. Contemporary MAS NMR yields atomic-level insights into structure and dynamics of an astounding range of biological systems, many of which cannot be studied by other methods. With the advent of fast MAS, proton detection, and novel pulse sequences, large supramolecular assemblies, such as cytoskeletal proteins and intact viruses, are now accessible for detailed analysis. In this review, we will discuss the current MAS NMR methodologies that enable characterization of complex biomolecular systems and will present examples of applications to several classes of assemblies comprising bacterial and mammalian cytoskeleton as well as human immunodeficiency virus 1 and bacteriophage viruses. The body of work reviewed herein is representative of the recent advancements in the field, with respect to the complexity of the systems studied, the quality of the data, and the significance to the biology.

Magic angle spinning NMR of viruses

Viruses, relatively simple pathogens, are able to replicate in many living organisms and to adapt to various environments. Conventional atomic-resolution structural biology techniques, X-ray crystallography and solution NMR spectroscopy provided abundant information on the structures of individual proteins and nucleic acids comprising viruses; however, viral assemblies are not amenable to analysis by these techniques because of their large size, insolubility, and inherent lack of long-range order. In this article, we review the recent advances in magic angle spinning NMR spectroscopy that enabled atomic-resolution analysis of structure and dynamics of large viral systems and give examples of several exciting case studies.

Magic-angle spinning NMR of intact bacteriophages: insights into the capsid, DNA and their interface

Bacteriophages are viruses that infect bacteria. They are complex macromolecular assemblies, which are composed of multiple protein subunits that protect genomic material and deliver it to specific hosts. Various biophysical techniques have been used to characterize their structure in order to unravel phage morphogenesis. Yet, most bacteriophages are non-crystalline and have very high molecular weights, in the order of tens of MegaDaltons. Therefore, complete atomic-resolution characterization on such systems that encompass both capsid and DNA is scarce. In this perspective article we demonstrate how magic-angle spinning solid-state NMR has and is used to characterize in detail bacteriophage viruses, including filamentous and icosahedral phage. We discuss the process of sample preparation, spectral assignment of both capsid and DNA and the use of chemical shifts and dipolar couplings to probe the capsid-DNA interface, describe capsid structure and dynamics and extract structural differences between viruses.

The NMR-Rosetta capsid model of M13 bacteriophage reveals a quadrupled hydrophobic packing epitope

Filamentous phage are elongated semiflexible ssDNA viruses that infect bacteria. The M13 phage, belonging to the family inoviridae, has a length of ∼1 μm and a diameter of ∼7 nm. Here we present a structural model for the capsid of intact M13 bacteriophage using Rosetta model building guided by structure restraints obtained from magic-angle spinning solid-state NMR experimental data. The C5 subunit symmetry observed in fiber diffraction studies was enforced during model building. The structure consists of stacked pentamers with largely alpha helical subunits containing an N-terminal type II β-turn; there is a rise of 16.6-16.7 Å and a tilt of 36.1-36.6° between consecutive pentamers. The packing of the subunits is stabilized by a repeating hydrophobic stacking pocket; each subunit participates in four pockets by contributing different hydrophobic residues, which are spread along the subunit sequence. Our study provides, to our knowledge, the first magic-angle spinning NMR structure of an intact filamentous virus capsid and further demonstrates the strength of this technique as a method of choice to study noncrystalline, high-molecular-weight molecular assemblies.

Complete chemical shift assignment of the ssDNA in the filamentous bacteriophage fd reports on its conformation and on its interface with the capsid shell

The fd bacteriophage is a filamentous virus consisting of a circular single-stranded DNA (ssDNA) wrapped by thousands of copies of a major coat protein subunit (the capsid). The coat protein subunits are mostly α-helical and curved, and are arranged in the capsid in consecutive pentamers related by a translation along the main viral axis and a rotation of ~36° (C5S2 symmetry). The DNA is right-handed and helical, but information on its structure and on its interface with the capsid is incomplete. We present here an approach for assigning the DNA nucleotides and studying its interactions with the capsid by magic-angle spinning solid-state NMR. Capsid contacts with the ssDNA are obtained using a two-dimensional (13)C-(13)C correlation experiment and a proton-mediated (31)P-(13)C polarization transfer experiment, both acquired on an aromatic-unlabeled phage sample. Our results allow us to map the residues that face the interior of the capsid and to show that the ssDNA-capsid interactions are sustained mainly by electrostatic interactions between the positively charged lysine side chains and the phosphate backbone. The use of natural abundance aromatic amino acids in the growth media facilitated the complete assignment of the four nucleotides and the observation of internucleotide contacts. Using chemical shift analysis, our study shows that structural features of the deoxyribose carbons reporting on the sugar pucker are strikingly similar to those observed recently for the Pf1 phage. However, the ssDNA-protein interface is different, and chemical shift markers of base pairing are different. This experimental approach can be utilized in other filamentous and icosahedral bacteriophages, and also in other biomolecular complexes involving structurally and functionally important DNA-protein interactions.

Recombinant bacteriophages as gold binding bio-templates

Bacteriophages are nano-sized virion particles infecting bacteria. In this study, it is shown that metal binding properties of filamentous fd-bacteriophages can be enhanced by genetic engineering. Quartz crystal microbalance (QCM) analyses, UV-vis absorption spectra measurements and scanning electron microscopy (SEM) imaging revealed that expression of MMM short amino acid sequence on major coat protein p8 facilitates recombinant MMM-phage binding to Au surfaces and nanoparticles (NPs) via gold-sulfur (AuS) interaction. Electroless deposition of Au particles on phage assemblies was investigated upon chemical reduction reaction with NaBH4 at different HAuCl4 precursor concentrations. Energy dispersive X-ray spectroscopy (EDX) measurements confirmed the presence of Au on both AuNP decorated and chemically metallized phage structures. Further studies on patterning and controlled immobilization of recombinant bacteriophages on specific surfaces may contribute to bio-templated nanowire development field and biosensor application studies.

Structural comparison of mouse and human α-synuclein amyloid fibrils by solid-state NMR

Fibrillar α-synuclein (AS) is the major component of Lewy bodies, the pathological hallmark of Parkinson's disease. Mouse AS (mAS) aggregates much faster than human AS (hAS), although mAS differs from hAS at only seven positions in its primary sequence. Currently, little is known about the site-specific structural differences between mAS and hAS fibrils. Here, we applied state-of-the-art solid-state nuclear magnetic resonance (ssNMR) methods to structurally characterize mAS fibrils. The assignment strategy employed a set of high-resolution 2D and 3D ssNMR spectra recorded on uniformly [(13)C, (15)N], [1-(13)C]glucose, and [2-(13)C]glucose labeled mAS fibrils. An almost complete resonance assignment (96% of backbone amide (15)N and 93% of all (13)C nuclei) was obtained for residues from Gly41 to Val95, which form the core of mAS fibrils. Six β-strands were identified to be within the fibril core of mAS based on a secondary chemical shift and NHHC analysis. Intermolecular (13)C:(15)N labeled restraints obtained from mixed 1:1 (13)C/(15)N-labeled mAS fibrils reveal a parallel, in-register supramolecular β-sheet arrangement. The results were compared in detail to recent structural studies on hAS fibrils and indicate the presence of a structurally conserved motif comprising residues Glu61-Lys80.