Biology subjects

Peckham, M.

Publications and source records attributed to Peckham, M..

9 recordsLinked to original sources

bioRxiv2026

Using iPALM to determine protein organisation in cardiac muscle Z-discs

Sarcomeres, the basic repeating unit of striated muscle, are joined together by crosslinked actin filaments found at the boundaries of muscle sarcomeres, termed Z-discs. Z-discs play a key role in cardiac signalling and disease, however, the arrangement and function of many of the proteins present in the Z-disc remain to be understood. Here, we determined the organisation of 3 key proteins, ZASP, [a]-Actinin-2 and the Z1Z2 epitope of titin, located within the Z-disc. We fluorescently labelled these proteins in cardiac myofibrils using Adhirons specific to each protein and used interferometric photoactivated localization microscopy (iPALM) to obtain the 3D position of these proteins to a high precision (<10nm in x,y,z). We then used PERPL (Pattern Extraction from Relative Positions of Localisations) to analyse patterns in the relative positions of the proteins and reveal their underlying organisation. This analysis revealed that ZASP and [a]-Actinin-2 have a similar repeating organisation, but that the organisation of Z1Z2 is different.

biophysics↗

bioRxiv2025

Cryo-EM structure of shutdown human non-muscle myosin 2A

Determining the high-resolution structure of the widely expressed non-muscle myosin 2A (NM2A), in its dephosphorylated shutdown state, is important in understanding its regulation and disease roles. In shutdown molecules, the coiled-coil tail wraps around the myosin heads preventing them from forming filaments and binding to actin. We have solved the shutdown structure of NM2A to a global resolution of 3.0 [A] in the heads region, and 6.3 [A] for the whole molecule. This reveals specific ionic interactions that explain why the path of the coiled coil and the shutdown mechanism for NM2A differs from that of {beta}-cardiac myosin and provides key insight into how specific mutations likely destabilize the shutdown state, leading to disease.

biochemistry↗

bioRxiv2024

The role of MEGF10 in myoblast fusion and hypertrophic response to overload of skeletal muscle

Biallelic mutations in multiple EGF domain protein 10 (MEGF10) gene cause EMARDD (early myopathy, areflexia, respiratory distress and dysphagia) in humans, a severe recessive myopathy, associated with reduced numbers of PAX7 positive satellite cells. To better understand the role of MEGF10 in satellite cells, we overexpressed human MEGF10 in mouse H-2kb-tsA58 myoblasts and found that it inhibited fusion. Addition of purified extracellular domains of human MEGF10, with (ECD) or without (EGF) the N-terminal EMI domain to H-2kb-tsA58 myoblasts, showed that the ECD was more effective at reducing myoblast adhesion and fusion by day 7 of differentiation, yet promoted adhesion of myoblasts to non-adhesive surfaces, highlighting the importance of the EMI domain in these behaviours. We additionally tested the role of Megf10 in vivo using transgenic mice with reduced (Megf10+/-) or no (Megf10-/-) Megf10. We found that the extensor digitorum longus muscle had fewer Pax7 positive satellite cell nuclei and was less able to undergo hypertrophy in response to muscle overload concomitant with a lower level of satellite cell activation. Taken together, our data suggest that MEGF10 may promote satellite cell adhesion and survival and prevent premature fusion helping to explain its role in EMARDD.

cell biology↗

bioRxiv2024

A Multiscale approach reveals the molecular architecture of the autoinhibited kinesin KIF5A.

Kinesin-1 is a microtubule motor that transports cellular cargo along microtubules. KIF5A is one of three kinesin-1 isoforms in humans, all of which are autoinhibited by an interaction between the motor and an IAK motif in the proximal region of the C-terminal tail. The C-terminal tail of KIF5A is [~]80 residues longer than the other two kinesin-1 isoforms (KIF5B and KIF5C) and it is unclear if it contributes to autoinhibition. Mutations in KIF5A cause neuronal diseases and could affect autoinhibition, as reported for a mutation that skips exon 27, altering its C-terminal sequence. Here, we combined negative-stain electron microscopy, crosslinking mass spectrometry (XL-MS) and AlphaFold2 structure prediction to determine the molecular architecture of the full-length autoinhibited KIF5A homodimer, in the absence of light chains. We show that KIF5A forms a compact, bent conformation, through a bend between coiled coils 2 and 3, around P687. XL-MS of WT KIF5A revealed extensive interactions between residues in the motor, between coiled-coil 1 and the motor, between coiled-coils 1 and 2, with coiled coils 3 and 4, and the proximal region of the C-terminal tail and the motor in the autoinhibited state, but not between the distal C-terminal region and the rest of the molecule. While negative stain electron microscopy of exon-27 KIF5A splice mutant showed the presence of autoinhibited molecules, XL-MS analysis suggested that its autoinhibited state is more labile. Our model offers a conceptual framework for understanding how mutations within the motor and stalk domain may affect motor activity.

cell biology↗

bioRxiv2023

Human light meromyosin mutations linked to skeletal myopathies disrupt the coiled coil structure and myosin head sequestration

Myosin heavy chains encoded by MYH7 and MYH2 are among the most abundant proteins in human skeletal muscle. After decades of intense research using a wide range of biophysical and biological approaches, their functions have begun to be elucidated. Despite this, it remains unclear how mutations in these genes and resultant proteins disrupt myosin structure and function, inducing pathological states and skeletal myopathies termed myosinopathies. Here, we have analysed the effects of several common MYH7 and MYH2 mutations located in light meromyosin (LMM) using a broad range of approaches. We determined the secondary structure and filament forming capabilities of expressed and purified LMM constructs in vitro, performed in-silico modelling of LMM constructs, and evaluated the incorporation of eGFP-myosin heavy chain constructs into sarcomeres in cultured myotubes. Using muscle biopsies from patients, we applied Mant-ATP chase protocols to estimate the proportion of myosin heads that were super-relaxed, X-ray diffraction measurements to estimate myosin head order and myofibre mechanics to investigate contractile function. We found that human MYH7 and MYH2 LMM mutations commonly disrupt myosin coiled-coil structure and packing of filaments in vitro; decrease the myosin super-relaxed state in vivo and increase the basal myosin ATP consumption; but are not associated with myofibre contractile deficits. Altogether, these findings indicate that the structural remodelling resulting from LMM mutations induces a pathogenic state in which formation of shutdown heads is impaired, thus increasing myosin head ATP demand in the filaments, rather than affecting contractility. These key findings will help in the design of future therapies for myosinopathies.

physiology↗

bioRxiv2023

Exploiting cryo-EM structures of actomyosin-5a to reveal the physical properties of its lever

Myosin 5a (Myo5a) is a dimeric processive motor protein that transports cellular cargos along actin filaments. Its long lever is responsible for its large powerstroke, step size and load-bearing ability. Little is known about the levers structure and physical properties, and how they contribute to walking mechanics. Using cryo-electron microscopy and molecular dynamics simulations, we resolved the structure of monomeric Myo5a, comprising the motor domain and full-length lever, bound to F-actin. The range of its lever conformations revealed its physical properties, how stiffness varies along its length and predicts a large, 35 nm, working stroke. Thus, the newly released trail head in a dimeric Myo5a would only need to perform a small diffusive search for its new binding site on actin, and stress would only be generated across the dimer once phosphate is released from the lead head, revealing new insight into the walking behaviour of Myo5a.

biophysics↗

bioRxiv2021

RNASeq analysis of a Pax3-expressing myoblast clone in-vitro and effect of culture surface stiffness on differentiation.

Skeletal muscle satellite cells cultured on soft surfaces (12kPa) show improved differentiation than cells cultured on stiff surfaces (approximately 100kPa). To better understand the reasons for this, we performed an RNA-Seq analysis for a single satellite cell clone (C1F) derived from the H2kb-tsA58 immortomouse, which differentiates into myotubes under tightly regulated conditions (withdrawal of {gamma}-interferon, 37{degrees}C). As expected, the largest change in overall gene expression occurred at day 1, as cells switch from proliferation to differentiation. Surprisingly, further analysis showed that proliferating C1F cells express Pax3 and not Pax7, confirmed by immunostaining, yet their subsequent differentiation into myotubes is normal, and enhanced on softer surfaces, as evidenced by significantly higher expression levels of myogenic regulatory factors, sarcomeric genes, enhanced fusion and improved myofibrillogenesis. Levels of RNA encoding extracellular matrix structural constituents and related genes were consistently upregulated on hard surfaces, suggesting that a consequence of differentiating satellite cells on hard surfaces is that they attempt to manipulate their niche prior to differentiating. This comprehensive RNASeq dataset will be a useful resource for understanding Pax3 expressing cells.

cell biology↗

bioRxiv2020

Nanoscale pattern extraction from relative positions of sparse 3D localisations

We present a method for extracting high-resolution ordered features from localisation microscopy data by analysis of relative molecular positions in 2D or 3D. This approach allows pattern recognition at sub-1% protein detection efficiencies, in large and heterogeneous samples, and in 2D and 3D datasets. We used this method to infer ultrastructure of the nuclear pore, the cardiomyocyte Z-disk, DNA origami structures and the centriole.

cell biology↗

bioRxiv2018

Persistent Chikungunya Virus Replication in Human Cells is Associated with Presence of Stable Cytoplasmic Granules Containing Non-structural Protein 3

Chikungunya virus (CHIKV), a mosquito-borne human pathogen, causes a disabling disease characterized by severe joint pain that can persist for weeks, months or even years in patients. The non-structural protein 3 (nsP3) plays essential roles during acute infection, but little is known about the function of nsP3 during chronic disease. Here, we used sub-diffraction multi-color microscopy for a spatial and temporal analysis of CHIKV nsP3 within human cells that persistently replicate viral RNA. Round cytoplasmic granules of various sizes (i) contained nsP3 and G3BP Stress Granule Assembly factor; (ii) were next to double-stranded RNA foci, and nsP1-positive structures; and (iii) made contact with markers of the cytoskeleton and cellular structures, such as early endosomes and nucleopores. Analysis of protein turnover and mobility by live-cell microscopy revealed that granules could persist for hours to days, can accumulate newly synthesized protein, and move at differently through the cytoplasm. Granules also had a static internal architecture and were stable in cell lysates. Whereas cells with active replication and stable nsP3-granules did not respond to oxidative stress, refractory cells that had cleared the non-cytotoxic replicon could. In summary, nsP3 can form uniquely stable granular structures that persist long-term within the host cell. This continued presence of viral and cellular protein-complexes has implications for the study of the pathogenic consequences of lingering CHIKV infection and the development of strategies to mitigate the burden of chronic musculoskeletal disease brought about by a medically important arthropod-borne virus (arbovirus).\n\nImportanceChikungunya virus (CHIKV) is a re-emerging alphavirus transmitted by mosquitos and causes widespread transient sickness but also chronic disease affecting muscles and joints. Although no approved vaccines or antivirals are available, a better understanding of the viral life cycle and the role of individual viral proteins can aid in identifying new therapeutic targets. Advances in microscopy and persistent CHIKV model systems now allow researchers to study viral proteins within controlled laboratory environments. Here we established human cells that stably replicate viral RNA and express a tagged version of non-structural protein 3. The ability to track this viral protein within the host cell and during persistent replication can benefit fundamental research efforts to better understand long-term consequences of the persistence of viral protein complexes and thereby provide the foundation for new therapeutic targets to control CHIKV infection and treat chronic disease symptoms.

microbiology↗