Identification and function of conformational dynamics in the multidomain GTPase dynamin
Vesicle release upon endocytosis requires membrane fission, catalyzed by the large GTPase dynamin. Dynamin contains five domains that together orchestrate its mechanochemical activity. Hydrogen–deuterium exchange coupled with mass spectrometry revealed global nucleotide- and membrane-binding-dependent conformational changes, as well as the existence of an allosteric relay element in the α2S helix of the dynamin stalk domain. As predicted from structural studies, FRET analyses detect large movements of the pleckstrin homology domain (PHD) from a ‘closed’ conformation docked near the stalk to an ‘open’ conformation able to interact with membranes. We engineered dynamin constructs locked in either the closed or open state by chemical cross-linking or deletion mutagenesis and showed that PHD movements function as a conformational switch to regulate dynamin self-assembly, membrane binding, and fission. This PHD conformational switch is impaired by a centronuclear myopathy-causing disease mutation, S619L, highlighting the physiological significance of its role in regulating dynamin function. Together, these data provide new insight into coordinated conformational changes that regulate dynamin function and couple membrane binding, oligomerization, and GTPase activity during dynamin-catalyzed membrane fission.
This article summarizes the clinical and genetic aspects of these disorders. RECENT FINDINGS Historically, diagnoses of congenital muscular dystrophy and congenital myopathy have been made by clinical features and histopathology; however, recent advances in genetics have changed diagnostic practice by relying more heavily on genetic findings. This article reviews the clinical and genetic features of the most common congenital muscular dystrophies including laminin subunit alpha 2 (LAMA2)–related (merosin deficient), collagen VI–related, and α-dystroglycan–related congenital muscular dystrophies a...
Publication date: January 2020Source: Journal of Comparative Pathology, Volume 174Author(s): K. Kamio, Y. Takahashi, K. Ishihara, A. Sekiya, S. Kato, I. Shimanuki, M. Ide, H. FuruokaSummaryHistopathological examination was performed on skeletal and diaphragmatic muscles from an 8-month-old male crossbred calf showing abnormal gait and tremor of the hindlimbs. There were numerous round fibres with centrally placed nuclei forming nuclear chains in longitudinal sections, associated with interstitial fibrosis or adipose tissue infiltration. On nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR) staining, some mus...
Centronuclear myopathy (CNM) is a rare congenital myopathy characterized by the morphological feature of centrally located nuclei in a large number of muscle fibers. CNM is related to several causative genes: dynamin 2 (DNM2), myotubularin (MTM1), amphiphysin 2 (BIN1), and ryanodine receptor 1 (RYR1) . DNM2-related CNM (DNM2-CNM) is an autosomal-dominant inherited disease that accounts for about 50% of CNM cases . Although DNM2-CNM has shown a variety of clinical manifestations, from severe neonatal onset to mild adult onset, most patients present with slowly progressive muscle weakness in the distal or sometimes pro...
ActiMyo ® is a device developed to evaluate the physical condition of patients suffering with movement disorders. It contains three-axis accelerometer, gyroscope, and magnetometer which allow recording daily life movements of patients in their usual environment using a wearable device. ActiMyo® has been t ested as an outcome measure in several trials involving ambulant and non-ambulant patients with neuromuscular disease as Duchenne muscular dystrophy (DMD), spinal muscular atrophy (SMA), or facio scapulohumeral dystrophy (FSHD).
Duchenne muscular dystrophy (DMD) is caused by the lack of dystrophin, a protein that connects the extracellular matrix to the cytoskeleton in muscle fibres. DMD boys develop progressive muscle wasting, leading to cardiac and respiratory failure and premature death. X-linked myotubular (centronuclear) myopathy (XLMTM) is a very severe myopathy characterized by generalized hypotonia from birth and death of most patients before the age of 2. Our recent preclinical data in mice demonstrated that tamoxifen (a drug used against breast cancer) may be helpful for boys with DMD and XLMTM.
Mutations in DNM2, encoding dynamin 2, an ubiquitously expressed GTPase, cause the autosomal dominant centronuclear myopathy (AD-CNM). Most of the AD-CNM mutations in DNM2 (such as S619L) are gain-of-function mutations leading to an increased GTPase activity. So far, DNM2 AD-CNM mutations have only been modelled transiently in zebrafish through the injection of mutated mRNA. mRNA injected larvae disclosed a severe phenotype with structural and functional abnormalities of the triad (Gibbs et al 2013).
Centronuclear myopathy (CNM) is an inherited neuromuscular disorder characterized by the presence of hypotrophic myofibers with centrally placed nuclei on muscle biopsies. CNM exists in 3 forms: i) X-linked recessive caused by mutations in the MTM gene encoding for the myotubularin protein (OMIM 310400), ii) autosomal dominant caused by mutations in the DNM2 gene encoding for the dynamin 2 protein (OMIM 160150) and iii) autosomal recessive form due to mutations in the BIN1 gene encoding for the amphyphysin 2 protein (OMIM 255200).
X-linked myotubular myopathy (XLMTM) is a severe congenital myopathy due to mutations in MTM1 encoding a 3-phosphoinositides phosphatase myotubularin. XLMTM patients display severe generalized hypotonia at birth accompanied by respiratory insufficiency and pathologically show small-size fibers with peripheral halo, centrally located nuclei, disorganized perinuclear organelles in the muscle. Among 78 patients with pathologically diagnosed as XLMTM in our cohort, causative mutations were not identified in 20 cases by targeted re-sequencing panel for congenital myopathy, MTM1 Sanger sequencing nor Whole-exome sequencing.
XLMTM is a rare disease caused by mutations in the MTM1 gene, leading to profound muscle weakness, respiratory failure and early death. INCEPTUS (NCT02704273) is a prospective, non-interventional study in patients (pts) ≤4 years old to characterize the course and natural history of XLMTM using neuromuscular and respiratory assessments and to identify adverse events (AEs). INCEPTUS will generate within-pt control data to support a Phase 1/2 gene therapy clinical trial (ASPIRO). As of 22MAR19, 32 male pts (0.3-4.6 years of age) have been enrolled and assessed every 3 months for up to 24 months.
Centronuclear myopathies (CNM) are a group of severe muscle diseases for which no effective therapy is currently available. The most severe and neonatal X-linked form is known as myotubular myopathy and caused by loss-of-function mutations in Myotubularin (MTM1), while the main autosomal dominant form is due to mutations in Dynamin 2 (DNM2). We previously showed that genetic reduction of DNM2 expression in Mtm1 knockout (Mtm1KO) mice prevents development of muscle pathology. We are now investigating skeletal muscle targeting of Dnm2 reduction in mice.