Myosin V exhibits a high duty cycle and large unitary displacement

Myosin V is a double-headed unconventional myosin that has been implicated in organelle transport. To perform this role, myosin V may have a high duty cycle. To test this hypothesis and understand the properties of this molecule at the molecular level, we used the laser trap and in vitro motility assay to characterize the mechanics of heavy meromyosin–like fragments of myosin V (M5HMM) expressed in the Baculovirus system. The relationship between actin filament velocity and the number of interacting M5HMM molecules indicates a duty cycle of ≥50%. This high duty cycle would allow actin filament translocation and thus organelle transport by a few M5HMM molecules. Single molecule displacement data showed predominantly single step events of 20 nm and an occasional second step to 37 nm. The 20-nm unitary step represents the myosin V working stroke and is independent of the mode of M5HMM attachment to the motility surface or light chain content. The large M5HMM working stroke is consistent with the myosin V neck acting as a mechanical lever. The second step is characterized by an increased displacement variance, suggesting a model for how the two heads of myosin V function in processive motion

Literacy outcomes for Deaf and Hard of Hearing primary school children: A cohort comparison study

Purpose: This study compared the language and literacy of two cohorts of children with severe-profound hearing loss, recruited 10 years apart, to determine whether outcomes had improved in line with the introduction of newborn hearing screening and access to improved hearing aid technology. Method: Forty-two deaf children, aged 5 -7 years with a mean unaided loss of 102 DB, were assessed on language, reading and phonological skills. Their performance was compared to that of a similar group of 32 deaf children assessed 10 years earlier, and also a group of 40 hearing children of similar single word reading ability. Results: English vocabulary was significantly higher in the new cohort, although it was still below chronological age. Phonological awareness and reading ability had not significantly changed over time. In both cohorts English vocabulary predicted reading but phonological awareness was only a significant predictor for the new cohort. Conclusions: The current results show that vocabulary knowledge of children with severe-profound hearing loss has improved over time but there has not been a commensurate improvement in phonological skills or reading. They suggest that children with severe-profound hearing loss will require continued support to develop robust phonological coding skills to underpin reading

The R403Q Myosin Mutation Implicated in Familial Hypertrophic Cardiomyopathy Causes Disorder at the Actomyosin Interface

Mutations in virtually all of the proteins comprising the cardiac muscle sarcomere have been implicated in causing Familial Hypertrophic Cardiomyopathy (FHC). Mutations in the beta-myosin heavy chain (MHC) remain among the most common causes of FHC, with the widely studied R403Q mutation resulting in an especially severe clinical prognosis. In vitro functional studies of cardiac myosin containing the R403Q mutation have revealed significant changes in enzymatic and mechanical properties compared to wild-type myosin. It has been proposed that these molecular changes must trigger events that ultimately lead to the clinical phenotype.Here we examine the structural consequences of the R403Q mutation in a recombinant smooth muscle myosin subfragment (S1), whose kinetic features have much in common with slow beta-MHC. We obtained three-dimensional reconstructions of wild-type and R403Q smooth muscle S1 bound to actin filaments in the presence (ADP) and absence (apo) of nucleotide by electron cryomicroscopy and image analysis. We observed that the mutant S1 was attached to actin at highly variable angles compared to wild-type reconstructions, suggesting a severe disruption of the actin-myosin interaction at the interface.These results provide structural evidence that disarray at the molecular level may be linked to the histopathological myocyte disarray characteristic of the diseased state

MHC-IIB Filament Assembly and Cellular Localization Are Governed by the Rod Net Charge

Actin-dependent myosin II molecular motors form an integral part of the cell cytoskeleton. Myosin II molecules contain a long coiled-coil rod that mediates filament assembly required for myosin II to exert its full activity. The exact mechanisms orchestrating filament assembly are not fully understood., negatively-charged regions of the coiled-coil were found to play an important role by controlling the intracellular localization of native MHC-IIB. The entire positively-charged region is also important for intracellular localization of native MHC-IIB.A correct distribution of positive and negative charges along myosin II rod is a necessary component in proper filament assembly and intracellular localization of MHC-IIB