Structure and dynamics of rotary V<Subscript>1</Subscript> motor

Rotary ATPases are unique rotary molecular motors that function as energy conversion machines. Among all known rotary ATPases, F₁-ATPase is the best characterized rotary molecular motor. There are many high-resolution crystal structures and the rotation dynamics have been investigated in detail by extensive single-molecule studies. In contrast, knowledge on the structure and rotation dynamics of V₁-ATPase, another rotary ATPase, has been limited. However, recent high-resolution structural studies and single-molecule studies on V₁-ATPase have provided new insights on how the catalytic sites in this molecular motor change its conformation during rotation driven by ATP hydrolysis. In this review, we summarize recent information on the structural features and rotary dynamics of V₁-ATPase revealed from structural and single-molecule approaches and discuss the possible chemomechanical coupling scheme of V₁-ATPase with a focus on differences between rotary molecular motors.     

Kinesin-II, the heteromeric kinesin

The kinesins constitute a large family of motor proteins which are responsible for the distribution of numerous organelles, vesicles and macromolecular complexes throughout the cell. One class of these molecular motors, kinesin-II, is unique in that these proteins are typically found as heterotrimeric complexes containing two different, though related, kinesin-like motor subunits, and a single nonmotor subunit. The heteromeric nature of these kinesins appears to have resulted in a class of combinatorial kinesins which can 'mix and match' different motor subunits. Another novel feature of these motors is that the activities of several kinesin-II representatives are essential in the assembly of motile and nonmotile cilia, a role not attributed to any other kinesin. This review presents a brief overview of the structure and biological functions of kinesin-II, the heteromeric kinesin.     

Assessing heterogeneity in oligomeric AAA+ machines

ATPases Associated with various cellular Activities (AAA+ ATPases) are molecular motors that use the energy of ATP binding and hydrolysis to remodel their target macromolecules. The majority of these ATPases form ring-shaped hexamers in which the active sites are located at the interfaces between neighboring subunits. Structural changes initiate in an active site and propagate to distant motor parts that interface and reshape the target macromolecules, thereby performing mechanical work. During the functioning cycle, the AAA+ motor transits through multiple distinct states. Ring architecture and placement of the catalytic sites at the intersubunit interfaces allow for a unique level of coordination among subunits of the motor. This in turn results in conformational differences among subunits and overall asymmetry of the motor ring as it functions. To date, a large amount of structural information has been gathered for different AAA+ motors, but even for the most characterized of them only a few structural states are known and the full mechanistic cycle cannot be yet reconstructed. Therefore, the first part of this work will provide a broad overview of what arrangements of AAA+ subunits have been structurally observed focusing on diversity of ATPase oligomeric ensembles and heterogeneity within the ensembles. The second part of this review will concentrate on methods that assess structural and functional heterogeneity among subunits of AAA+ motors, thus bringing us closer to understanding the mechanism of these fascinating molecular motors.     

Kinesins in the nervous system

Both the development and the maintenance of neurons require a great deal of active cytoplasmic transport. Much of this transport is driven by microtubule motor proteins. Membranous organelles and other macromolecular assemblies bind motor proteins that then use cycles of adenosine 5'-triphosphate hydrolysis to move these 'cargoes' along microtubules. Different sets of cargoes are transported to distinct locations in the cell. The resulting differential distribution of materials almost certainly plays an important part in generating polarized neuronal morphologies and in maintaining their vectorial signalling activities. A number of different microtubule motor proteins function in neurons; presumably they are specialized for accomplishing different transport tasks. Questions about specific motor functions and the functional relationships between different motors present a great challenge. The answers will provide a much deeper understanding of fundamental transport mechanisms, as well as how these mechanisms are used to generate and sustain cellular asymmetries.     

Regulation of long-distance transport of mitochondria along microtubules

Mitochondria are cellular organelles of crucial importance, playing roles in cellular life and death. In certain cell types, such as neurons, mitochondria must travel long distances so as to meet metabolic demands of the cell. Mitochondrial movement is essentially microtubule (MT) based and is executed by two main motor proteins, Dynein and Kinesin. The organization of the cellular MT network and the identity of motors dictate mitochondrial transport. Tight coupling between MTs, motors, and the mitochondria is needed for the organelle precise localization. Two adaptor proteins are involved directly in mitochondria-motor coupling, namely Milton known also as TRAK, which is the motor adaptor, and Miro, which is the mitochondrial protein. Here, we discuss the active mitochondria transport process, as well as motor–mitochondria coupling in the context of MT organization in different cell types. We focus on mitochondrial trafficking in different cell types, specifically neurons, migrating cells, and polarized epithelial cells.     

Molecular motors: not quite like clockwork

Models commonly used to explain the mechanism of myosin motors typically include a power stroke that is attributed to a conformational change in the motor domain and amplified by a long lever arm that connects the motor domain to the cargo. Similar models have proved less enlightening in the case of microtubule motors, for which it may be more helpful to consider models involving thermally driven mechanisms. Received 9 November 2007; received after revision 7 December 2007; accepted 11 December 2007     

SecA,a remarkable nanomachine

Biological cells harbor a variety of molecular machines that carry out mechanical work at the nanoscale. One of these nanomachines is the bacterial motor protein SecA which translocates secretory proteins through the protein-conducting membrane channel SecYEG. SecA converts chemically stored energy in the form of ATP into a mechanical force to drive polypeptide transport through SecYEG and across the cytoplasmic membrane. In order to accommodate a translocating polypeptide chain and to release transmembrane segments of membrane proteins into the lipid bilayer, SecYEG needs to open its central channel and the lateral gate. Recent crystal structures provide a detailed insight into the rearrangements required for channel opening. Here, we review our current understanding of the mode of operation of the SecA motor protein in concert with the dynamic SecYEG channel. We conclude with a new model for SecA-mediated protein translocation that unifies previous conflicting data.     

The diversity of molecular motors: an overview

Rapid progress has recently been made in the identification and characterization of a large number of kinesin and myosin motor proteins. Recent work has uncovered roles for these motors in processes such as vesicle trafficking, cytoskeletal organization, and chromosome movements, to name a few. A series of reviews describing some of the significant advances in our understanding of the structure and function of myosins and kinesins is presented.     

Bidirectional motility of kinesin-5 motor proteins: structural determinants,cumulative functions and physiological roles

Mitotic kinesin-5 bipolar motor proteins perform essential functions in mitotic spindle dynamics by crosslinking and sliding antiparallel microtubules (MTs) apart within the mitotic spindle. Two recent studies have indicated that single molecules of Cin8, the Saccharomyces cerevisiae kinesin-5 homolog, are minus end-directed when moving on single MTs, yet switch directionality under certain experimental conditions (Gerson-Gurwitz et al., EMBO J 30:4942–4954, 2011; Roostalu et al., Science 332:94–99, 2011). This finding was unexpected since the Cin8 catalytic motor domain is located at the N-terminus of the protein, and such kinesins have been previously thought to be exclusively plus end-directed. In addition, the essential intracellular functions of kinesin-5 motors in separating spindle poles during mitosis can only be accomplished by plus end-directed motility during antiparallel sliding of the spindle MTs. Thus, the mechanism and possible physiological role of the minus end-directed motility of kinesin-5 motors remain unclear. Experimental and theoretical studies from several laboratories in recent years have identified additional kinesin-5 motors that are bidirectional, revealed structural determinants that regulate directionality, examined the possible mechanisms involved and have proposed physiological roles for the minus end-directed motility of kinesin-5 motors. Here, we summarize our current understanding of the remarkable ability of certain kinesin-5 motors to switch directionality when moving along MTs.     

Semi-synthesis and proposed structure of platelet-activating factor (P.A.F.): PAF-acether an alkyl ether analog of lysophosphatidylcholine]

We have studied the molecular structure of platelet-activating factor" (P.A.F.), a mediator of inflammation obtained from blood leukocytes, macrophages, and platelets themselves. We have semi-synthetized a substance that possesses all the known physicochemical and biological characteristics of P.A.F. from hog leukocytes. This was performed by successive methylation, hydrogenation, and acetylation of lysophosphatidylethanolamine plasmalogen. We therefore propose the following structure for P.A.F.: 1-0-alkyl-2-acetyl-glyceryl-3-phosphorylcholine. This molecular structure is not yet described among the numerous substances capable of inducing platelet aggregation and release.     

Three-dimensional structure of motor molecules

Images, calculated from electron micrographs, show the three-dimensional structures of microtubules and tubulin sheets decorated stoichiometrically with motor protein molecules. Dimeric motor domains (heads) of kinesin and ncd, the kinesin-related protein that moves in the reverse direction, each appeared to bind to tubulin in the same way, by one of their two heads. The second heads show an interesting difference in position that seems to be related to the directions of movement of the two motors. X-ray crystallographic results showing the structures of kinesin and ncd to be very similar at atomic resolution, and homologous also to myosin, suggest that the two motor families may use mechanisms that have much in common. Nevertheless, myosins and kinesins differ kinetically. Also, whereas conformational changes in the myosin catalytic domain are amplified by a long lever arm that connects it to the stalk domain, kinesin and ncd do not appear to possess a structure with a similar function but may rely on biased diffusion in order to move along microtubules.     

基于STM32的太阳能跟踪系统设计

基于先进Codex—M3内核的微处理器STM32,结合双电机驱动器与高精度光敏传感器,研究并设计了一套高精度太阳能跟踪系统。该系统以实时时间为基准精确追踪太阳位置,以光敏传感器进行误差修正,利用STM32优越的PWM方式控制电机,实现太阳能接受效率的最大化。实验结果表明,系统工作稳定可靠,基本实现了对太阳的实时跟踪。     

Proteomic interaction profiling reveals KIFC1 as a factor involved in early targeting of F508del-CFTR to degradation

Misfolded F508del-CFTR, the main molecular cause of the recessive disorder cystic fibrosis, is recognized by the endoplasmic reticulum (ER) quality control (ERQC) resulting in its retention and early degradation. The ERQC mechanisms rely mainly on molecular chaperones and on sorting motifs, whose presence and exposure determine CFTR retention or exit through the secretory pathway. Arginine-framed tripeptides (AFTs) are ER retention motifs shown to modulate CFTR retention. However, the interactions and regulatory pathways involved in this process are still largely unknown. Here, we used proteomic interaction profiling and global bioinformatic analysis to identify factors that interact differentially with F508del-CFTR and F508del-CFTR without AFTs (F508del-4RK-CFTR) as putative regulators of this specific ERQC checkpoint. Using LC–MS/MS, we identified kinesin family member C1 (KIFC1) as a stronger interactor with F508del-CFTR versus F508del-4RK-CFTR. We further validated this interaction showing that decreasing KIFC1 levels or activity stabilizes the immature form of F508del-CFTR by reducing its degradation. We conclude that the current approach is able to identify novel putative therapeutic targets that can be ultimately used to the benefit of CF patients.     

Biological functions and signaling of a transmembrane semaphorin,CD100/Sema4D

The semaphorin proteins were identified originally as axonal guidance factors functioning during neuronal development. In addition to this function, several semaphorins play diverse roles outside the nervous system. The class 4 semaphorin CD100/Sema4D, which utilizes plexin-B1 and CD72 as receptors, exerts important biological effects on a variety of cells, including the neuronal, epithelial and immune cells. Here, we review recent advances exploring the molecular mechanisms governing the biological functions of CD100/Sema4D.Received 1 July 2003; received after revision 25 July 2003; accepted 29 July 2003     

Research advances in gene therapy approaches for the treatment of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease of motor neurons that causes progressive muscle weakness, paralysis, and premature death. No effective therapy is available. Research in the motor neuron field continues to grow, and recent breakthroughs have demonstrated the possibility of completely achieving rescue in animal models of spinal muscular atrophy, a genetic motor neuron disease. With adeno-associated virus (AAV) vectors, gene transfer can be achieved with systemic non-invasive injection and minimal toxicity. In the context of this success, we review gene therapy approaches for ALS, considering what has been done and the possible future directions for effective application of the latest generation of vectors for clinical translation. We focus on recent developments in the areas of RNA/antisense-mediated silencing of specific ALS causative genes like superoxide dismutase-1 and other molecular pathogenetic targets, as well as the administration of neuroprotective factors with viral vectors. We argue that gene therapy offers new opportunities to open the path for clinical progress in treating ALS.     

Mitotic force generators and chromosome segregation

The mitotic spindle uses dynamic microtubules and mitotic motors to generate the pico-Newton scale forces that are needed to drive the mitotic movements that underlie chromosome capture, alignment and segregation. Here, we consider the biophysical and molecular basis of force-generation for chromosome movements in the spindle, and, with reference to the Drosophila embryo mitotic spindle, we briefly discuss how mathematical modeling can complement experimental analysis to illuminate the mechanisms of chromosome-to-pole motility during anaphase A and spindle elongation during anaphase B.     

Structure of the gap junction channel and its implications for its biological functions

Gap junctions consist of arrays of intercellular channels composed of integral membrane proteins called connexin in vertebrates. Gap junction channels regulate the passage of ions and biological molecules between adjacent cells and, therefore, are critically important in many biological activities, including development, differentiation, neural activity, and immune response. Mutations in connexin genes are associated with several human diseases, such as neurodegenerative disease, skin disease, deafness, and developmental abnormalities. The activity of gap junction channels is regulated by the membrane voltage, intracellular microenvironment, interaction with other proteins, and phosphorylation. Each connexin channel has its own property for conductance and molecular permeability. A number of studies have tried to reveal the molecular architecture of the channel pore that should confer the connexin-specific permeability/selectivity properties and molecular basis for the gating and regulation. In this review, we give an overview of structural studies and describe the structural and functional relationship of gap junction channels.     

Gathering up meiotic telomeres: a novel function of the microtubule-organizing center

During meiosis, telomeres cluster and promote homologous chromosome pairing. Telomere clustering depends on conserved SUN and KASH domain nuclear membrane proteins, which form a complex called the linker of nucleoskeleton and cytoskeleton (LINC) and connect telomeres with the cytoskeleton. It has been thought that LINC-mediated cytoskeletal forces induce telomere clustering. However, how cytoskeletal forces induce telomere clustering is not fully understood. Recent study of fission yeast has shown that the LINC complex forms the microtubule-organizing center (MTOC) at the telomere, which has been designated as the “telocentrosome”, and that microtubule motors gather telomeres via telocentrosome-nucleated microtubules. This MTOC-dependent telomere clustering might be conserved in other eukaryotes. Furthermore, the MTOC-dependent clustering mechanism appears to function in various other biological events. This review presents an overview of the current understanding of the mechanism of meiotic telomere clustering and discusses the universality of the MTOC-dependent clustering mechanism.