Functional studies of individual myosin molecules

One must reconstitute the functions of interest from purified proteins

I am often asked by students and younger colleagues and now by the editors of this issue to tell the history of the development of the in vitro motility assay and the dual-beam single-molecule laser trap assay for myosin-driven actin filament movement, used widely as key assays for understanding how both muscle and nonmuscle myosin molecular motors work. As for all discoveries, the history of the development of the myosin assays involves many people who are not authors of the final publications, but without whom the assays would not have been developed as they are. Also, early experiences shape how one develops ideas and experiments, and influence future discoveries in major ways. I am pleased here to trace my own path and acknowledge the many individuals involved and my early science experiences that led to the work I and my students, postdoctoral fellows, and sabbatical visitors did to develop these assays. Mentors are too often overlooked in historical descriptions of discoveries, and my story starts with those who mentored me.

Application of optical tweezers in cardiovascular research: More than just a measuring tool

Recent advances in the field of optical tweezer technology have shown intriguing potential for applications in cardiovascular medicine, bringing this laboratory nanomechanical instrument into the spotlight of translational medicine. This article summarizes cardiovascular system findings generated using optical tweezers, including not only rigorous nanomechanical measurements but also multifunctional manipulation of biologically active molecules such as myosin and actin, of cells such as red blood cells and cardiomyocytes, of subcellular organelles, and of microvessels in vivo. The implications of these findings in the diagnosis and treatment of diseases, as well as potential perspectives that could also benefit from this tool, are also discussed.

Hypertrophic cardiomyopathy and the myosin mesa: viewing an old disease in a new light

The sarcomere is an exquisitely designed apparatus that is capable of generating force, which in the case of the heart results in the pumping of blood throughout the body. At the molecular level, an ATP-dependent interaction of myosin with actin drives the contraction and force generation of the sarcomere. Over the past six decades, work on muscle has yielded tremendous insights into the workings of the sarcomeric system. We now stand on the cusp where the acquired knowledge of how the sarcomere contracts and how that contraction is regulated can be extended to an understanding of the molecular mechanisms of sarcomeric diseases, such as hypertrophic cardiomyopathy (HCM). In this review we present a picture that combines current knowledge of the myosin mesa, the sequestered state of myosin heads on the thick filament, known as the interacting-heads motif (IHM), their possible interaction with myosin binding protein C (MyBP-C) and how these interactions can be abrogated leading to hyper-contractility, a key clinical manifestation of HCM. We discuss the structural and functional basis of the IHM state of the myosin heads and identify HCM-causing mutations that can directly impact the equilibrium between the 'on state' of the myosin heads (the open state) and the IHM 'off state'. We also hypothesize a role of MyBP-C in helping to maintain myosin heads in the IHM state on the thick filament, allowing release in a graded manner upon adrenergic stimulation. By viewing clinical hyper-contractility as the result of the destabilization of the IHM state, our aim is to view an old disease in a new light.

Role for myosin-V motor proteins in the selective delivery of Kv channel isoforms to the membrane surface of cardiac myocytes

RATIONALE

Kv1.5 (KCNA5) mediates the ultra-rapid delayed rectifier current that controls atrial action potential duration. Given its atrial-specific expression and alterations in human atrial fibrillation, Kv1.5 has emerged as a promising target for the treatment of atrial fibrillation. A necessary step in the development of novel agents that selectively modulate trafficking pathways is the identification of the cellular machinery controlling Kv1.5 surface density, of which little is yet known.

OBJECTIVE

To investigate the role of the unconventional myosin-V (MYO5A and MYO5B) motors in determining the cell surface density of Kv1.5.

METHODS AND RESULTS

Western blot analysis showed MYO5A and MYO5B expression in the heart, whereas disruption of endogenous motors selectively reduced IKur current in adult rat cardiomyocytes. Dominant negative constructs and short hairpin RNA silencing demonstrated a role for MYO5A and MYO5B in the surface trafficking of Kv1.5 and connexin-43 but not potassium voltage-gated channel, subfamily H (eag-related), member 2 (KCNH2). Live-cell imaging of Kv1.5-GFP and retrospective labeling of phalloidin demonstrated motility of Kv1.5 vesicles on actin tracts. MYO5A participated in anterograde trafficking, whereas MYO5B regulated postendocytic recycling. Overexpression of mutant motors revealed a selective role for Rab11 in coupling MYO5B to Kv1.5 recycling.

CONCLUSIONS

MYO5A and MYO5B control functionally distinct steps in the surface trafficking of Kv1.5. These isoform-specific trafficking pathways determine Kv1.5-encoded IKur in myocytes to regulate repolarizing current and, consequently, cardiac excitability. Therapeutic strategies that manipulate Kv1.5 selective trafficking pathways may prove useful in the treatment of arrhythmias.

Transcriptome analysis of newt lens regeneration reveals distinct gradients in gene expression patterns

Regeneration of the lens in newts is quite a unique process. The lens is removed in its entirety and regeneration ensues from the pigment epithelial cells of the dorsal iris via transdifferentiation. The same type of cells from the ventral iris are not capable of regenerating a lens. It is, thus, expected that differences between dorsal and ventral iris during the process of regeneration might provide important clues pertaining to the mechanism of regeneration. In this paper, we employed next generation RNA-seq to determine gene expression patterns during lens regeneration in Notophthalmus viridescens. The expression of more than 38,000 transcripts was compared between dorsal and ventral iris. Although very few genes were found to be dorsal- or ventral-specific, certain groups of genes were up-regulated specifically in the dorsal iris. These genes are involved in cell cycle, gene regulation, cytoskeleton and immune response. In addition, the expression of six highly regulated genes, TBX5, FGF10, UNC5B, VAX2, NR2F5, and NTN1, was verified using qRT-PCR. These graded gene expression patterns provide insight into the mechanism of lens regeneration, the markers that are specific to dorsal or ventral iris, and layout a map for future studies in the field.

Proteomic analysis of chicken embryonic trachea and kidney tissues after infection in ovo by avian infectious bronchitis coronavirus

Background

Avian infectious bronchitis (IB) is one of the most serious diseases of economic importance in chickens; it is caused by the avian infectious coronavirus (IBV). Information remains limited about the comparative protein expression profiles of chicken embryonic tissues in response to IBV infection in ovo. In this study, we analyzed the changes of protein expression in trachea and kidney tissues from chicken embryos, following IBV infection in ovo, using two-dimensional gel electrophoresis (2-DE) coupled with matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI-TOF-TOF MS).

Results

17 differentially expressed proteins from tracheal tissues and 19 differentially expressed proteins from kidney tissues were identified. These proteins mostly related to the cytoskeleton, binding of calcium ions, the stress response, anti-oxidative, and macromolecular metabolism. Some of these altered proteins were confirmed further at the mRNA level using real-time RT-PCR. Moreover, western blotting analysis further confirmed the changes of annexin A5 and HSPB1 during IBV infection.

Conclusions

To the best of our knowledge, we have performed the first analysis of the proteomic changes in chicken embryonic trachea and kidney tissues during IBV infection in ovo. The data obtained should facilitate a better understanding of the pathogenesis of IBV infection.

The selective role of myosin VI in lymphoid leukemia cell migration

Several myosin isotypes are discussed to be involved in the migration of various cells ranging from tumor cells to leukocytes. We investigated the involvement of myosins II and VI in the lymphoid leukemia cells lines Jurkat, NB4, Dohh-2, and Molt-4 by a three-dimensional, collagen-based migration assay. Down-regulation of myosin VI by siRNA significantly reduced the migratory activity of all cells, whereas the pharmacological inhibition of non-muscle myosin II using blebbistatin had only marginal influence. Therefore, in contrast to differentiated leukocytes and cells from solid tumors, myosin VI plays a crucial role in the migration of leukemic cells.

Navigating barriers: the challenge of directed secretion at the natural killer cell lytic immunological synapse

INTRODUCTION

Natural killer (NK) cells have an inherent ability to recognize and destroy a wide array of cells rendered abnormal by stress or disease. NK cells can kill a targeted cell by forming a tight interface-the lytic immunological synapse. This represents a dynamic molecular arrangement that over time progresses through a series of steps to ultimately deliver the contents of specialized organelles known as lytic granules.

DISCUSSION

In order to mediate cytotoxicity, the NK cell faces the challenge of mobilizing the lytic granules, polarizing them to the targeted cell, facilitating their approximation to the NK cell membrane, and releasing their contents.

CONCLUSION

This review is focused upon the final steps in accessing function through the lytic immunological synapse.

Ion channel trafficking: a new therapeutic horizon for atrial fibrillation

Atrial fibrillation (AF) is a common cardiac arrhythmia with potentially life-threatening complications. Drug therapies for treatment of AF that seek long-term maintenance of normal sinus rhythm remain elusive due in large part to proarrhythmic ventricular actions. Kv1.5, which underlies the atrial specific I(Kur) current, is a major focus of research efforts seeking new therapeutic strategies and targets. Recent work has shown a novel effect of antiarrhythmic drugs where compounds that block Kv1.5 channel current also can alter ion channel trafficking. This work further suggests that the pleiotropic effects of antiarrhythmic drugs may be separable. Although this finding highlights the therapeutic potential for selective manipulation of ion channel surface density, it also reveals an uncertainty regarding the specificity of modulating trafficking pathways without risk of off-target effects. Future studies may show that specific alteration of Kv1.5 trafficking can overcome the proarrhythmic limitations of current pharmacotherapy and provide an effective method for long-term cardioversion in AF.

Requirement of myosin Vb.Rab11a.Rab11-FIP2 complex in cholesterol-regulated translocation of NPC1L1 to the cell surface

Niemann-Pick C1-like 1 (NPC1L1) plays a critical role in the enterohepatic absorption of free cholesterol. Cellular cholesterol depletion induces the transport of NPC1L1 from the endocytic recycling compartment to the plasma membrane (PM), and cholesterol replenishment causes the internalization of NPC1L1 together with cholesterol via clathrin-mediated endocytosis. Although NPC1L1 has been characterized, the other proteins involved in cholesterol absorption and the endocytic recycling of NPC1L1 are largely unknown. Most of the vesicular trafficking events are dependent on the cytoskeleton and motor proteins. Here, we investigated the roles of the microfilament and microfilament-associated triple complex composed of myosin Vb, Rab11a, and Rab11-FIP2 in the transport of NPC1L1 from the endocytic recycling compartment to the PM. Interfering with the dynamics of the microfilament by pharmacological treatment delayed the transport of NPC1L1 to the cell surface. Meanwhile, inactivation of any component of the myosin Vb.Rab11a.Rab11-FIP2 triple complex inhibited the export of NPC1L1. Expression of the dominant-negative mutants of myosin Vb, Rab11a, or Rab11-FIP2 decreased the cellular cholesterol uptake by blocking the transport of NPC1L1 to the PM. These results suggest that the efficient transport of NPC1L1 to the PM is dependent on the microfilament-associated myosin Vb.Rab11a.Rab11-FIP2 triple complex.

Single-molecule biophysics: at the interface of biology, physics and chemistry

Single-molecule methods have matured into powerful and popular tools to probe the complex behaviour of biological molecules, due to their unique abilities to probe molecular structure, dynamics and function, unhindered by the averaging inherent in ensemble experiments. This review presents an overview of the burgeoning field of single-molecule biophysics, discussing key highlights and selected examples from its genesis to our projections for its future. Following brief introductions to a few popular single-molecule fluorescence and manipulation methods, we discuss novel insights gained from single-molecule studies in key biological areas ranging from biological folding to experiments performed in vivo.

How single molecule detection measures the dynamic actions of life

Biomolecules dynamically work in cells in which a variety of molecules assemble and interact in unique manner. The molecular mechanisms underlying several biological processes have been elucidated from the results obtained from the descriptions of cell function, from the snapshots of the structures of biomolecules involved in these processes, and from the biochemical properties of these reactions in vitro. Recently developed single molecule measurements have revealed the dynamic properties of the biomolecules that have been hidden in the data that have been averaged over large numbers of molecules in both ensemble measurement and in cells. Single molecule imaging and manipulation of single molecules have allowed the visualization of the dynamic operations of molecular motors, enzymatic reactions, structural dynamics of biomolecules, and cell signaling processes. The results have shown that the single molecule techniques are powerful tools to monitor the dynamic actions of biomolecules and their assemblies. This approach has been applied to a variety of fields within the life sciences. As new information emerges about the dynamic actions of biomolecules using methods of single molecule detection new views on how biological processes work will be revealed.

How single molecule detection measures the dynamic actions of life

Biomolecules dynamically work in cells in which a variety of molecules assemble and interact in unique manner. The molecular mechanisms underlying several biological processes have been elucidated from the results obtained from the descriptions of cell function, from the snapshots of the structures of biomolecules involved in these processes, and from the biochemical properties of these reactions in vitro. Recently developed single molecule measurements have revealed the dynamic properties of the biomolecules that have been hidden in the data that have been averaged over large numbers of molecules in both ensemble measurement and in cells. Single molecule imaging and manipulation of single molecules have allowed the visualization of the dynamic operations of molecular motors, enzymatic reactions, structural dynamics of biomolecules, and cell signaling processes. The results have shown that the single molecule techniques are powerful tools to monitor the dynamic actions of biomolecules and their assemblies. This approach has been applied to a variety of fields within the life sciences. As new information emerges about the dynamic actions of biomolecules using methods of single molecule detection new views on how biological processes work will be revealed.