Beyond Enzyme Kinetics
Clive R. Bagshaw in Biomolecular Kinetics, 2017
Motor proteins are involved with chemical–mechanical energy transduction. The chemical energy used by motor proteins is typically obtained from the hydrolysis of NTP or an ion concentration gradient. NTP hydrolysis is readily followed by standard enzymological assays, but in the absence of external mechanical coupling, the reaction generates only heat. To obtain full understanding, these assays must be combined with mechanical measurements to assess the work output. This field has benefited greatly from advances in single-molecule methods where, in favorable cases, chemical and mechanical properties can be measured simultaneously on the same molecule (Section 9.3) [233]. However, the advances in this area would not have occurred with such speed without background information obtained over the preceding century. Actin and myosin from skeletal muscle provided the paradigm for motor proteins because these proteins are easily purified from tissue and are arranged in a highly ordered filamentous form within the muscle. From knowledge of the detailed structure of the muscle, the ATPase activity, the macroscopic force, and contraction velocity, it was possible to deduce that contraction involved the repetitive action of elementary units, which generated forces of several pico-Newtons over about 10 nm distances, 40 years before single-molecule measurements were developed to test this proposal directly [74,76,234,235].
Pharmacologic Ascorbate Influences Multiple Cellular Pathways Preferentially in Cancer Cells
Qi Chen, Margreet C.M. Vissers in Cancer and Vitamin C, 2020
Microtubules act as tracks for cargo transport with the help of motor proteins (kinesin and dynein) in and out of the cells. The motor proteins kinesin and dynein associate with cargoes and transport them along microtubules. Tubulin posttranslational modifications are associated with the recruitment of specific types of motor molecules. For example, acetylated α-tubulin specifically interacts with kinesin 1 cargo complex, whereas tyrosinated α-tubulin interacts with kinesin 3 cargo complex [65]. Assuming from the fact that pharmacologic ascorbate enhanced α-tubulin acetylation, it is possible that cargo transport is influenced. Currently, there efforts have not been made to understand the effect of ascorbate on cargo transport mediated by motor proteins. This question is particularly important in neuronal transport, that ascorbate might have pathophysiologic or therapeutic implication for diseases of the nervous system. Microtubules in the axon organize into bundles and enable efficient transport of neurotransmitters. Such bundled microtubules are also observed in primary cilia and flagella, as well as in mitotic spindles. Often, these microtubules are marked by acetylation. Further research is required to address these intriguing questions.
Mitochondrial Dysfunction in Chronic Disease
Peter M. Tiidus, Rebecca E. K. MacPherson, Paul J. LeBlanc, Andrea R. Josse in The Routledge Handbook on Biochemistry of Exercise, 2020
Cells are constantly fine-tuning their energy requirements, namely during bouts of exercise. To generate enough ATP for each cell, mitochondria must be appropriately distributed throughout the cell. Cytoskeleton components form a series of microtubule filaments using α- and β-tubulin subunits which act as a platform for mitochondrial transport (82). Heavily characterized in neuronal cultures (140), actin and intermediate filaments aid in the cytoskeletal distribution of mitochondria. Movement of the mitochondria is achieved through the attachment of motor proteins to the microtubule filaments (63). Kinesin motor proteins move the mitochondria in the anterograde (+) direction, while dynein motor proteins move mitochondria in the retrograde (-) direction (107). The connection between mitochondria and the aforementioned motor proteins is accomplished through the mitochondrial motor/adaptor complex (119). At this junction, kinesin/dynein motor proteins attach to the adaptor protein Milton, which then attaches to mitochondrial Rho GTPases 1 and 2 (MIRO1/2) on the OMM (119).
Intraflagellar transport proteins are involved in thrombocyte filopodia formation and secretion
Published in Platelets, 2018
Uvaraj Radhakrishnan, Abdullah Alsrhani, Hemalatha Sundaramoorthi, Gauri Khandekar, Meghana Kashyap, Jannon L Fuchs, Brian D Perkins, Yoshihiro Omori, Pudur Jagadeeswaran
Intraflagellar transport (IFT) proteins are present mainly in cells that have either a primary cilium or motile cilia. These functionally conserved proteins are critical in the genesis and maintenance of cilia [1–3]. Different, but overlapping sets of IFT proteins compose two IFT complexes: Complex A is mainly for retrograde transport of substances back from the tip of the cilium, and Complex B is for anterograde transport from the base of the cilium to the tip [4,5]. The motor proteins kinesin and dynein move IFT particles with their cargo along microtubules in the anterograde and retrograde direction, respectively. The primary cilium is present in most vertebrate cell types and plays diverse roles in sensory transduction and other types of signaling [6,7]. Defects in IFT proteins can result in short or absent cilia, signaling abnormalities, and associated ciliopathy symptoms in humans and other mammals [8]. In zebrafish, IFT knockdowns and mutations also lead to phenotypic symptoms of defective cilia signaling [9–12].
Syntaphilin mediates axonal growth and synaptic changes through regulation of mitochondrial transport: a potential pharmacological target for neurodegenerative diseases
Published in Journal of Drug Targeting, 2023
Qing-Yun Wu, Hui-Lin Liu, Hai-Yan Wang, Kai-Bin Hu, Ping Liao, Sen Li, Zai-Yun Long, Xiu-Min Lu, Yong-Tang Wang
Two types of motor proteins, the kinesins family and the dyneins family, bind to microtubules. The kinesin superfamily has 14 families, of which Kinesin-1 family members (KIF5) are the main motors driving neuronal mitochondrial forward transport along microtubules [26]. Kinesin-1 is usually a heterotetramer composed of two light chains (KLC) and two heavy chains (KHC). KLC contributes to the association of Kinesin-1 with mitochondria and the regulation of activity, while KHC provides power by hydrolysing ATP and carries out axonal transport along the microtubule. Targeted disruption of KIF5 expression in mice inhibits mitochondrial motor function and leads to mitochondrial accumulation in the perinuclear region. Although mutations of the KHC gene in Drosophila melanogaster severely reduced mitochondrial transport in neurons, they were not completely eliminated, suggesting that other protein motors are involved in driving mitochondrial transport. In addition to KIF5, some members of the Kinesin-3 family are also involved in axonal mitochondrial transport [27]. However, the exact mechanism of their role in mitochondrial transport requires further investigation.
Formin proteins in megakaryocytes and platelets: regulation of actin and microtubule dynamics
Published in Platelets, 2019
Malou Zuidscherwoude, Hannah L.H. Green, Steven G. Thomas
mDia1 function has also been directly investigated in megakaryocytes. Pan et al. (48) used shRNA in human CD34+ derived megakaryocytes to knockdown mDia1 expression to approximately 50–60% of controls. In these cells, proplatelet formation (PPF) was increased, F-actin polymerisation was decreased and the stability of microtubules was increased, as assessed by increased Glu-tubulin (28,29). These data indicate that partial inactivation of mDia1 activity in mature megakaryocytes is required to allow proplatelet formation. This effect is proposed to be mediated through reducing actin-myosin contractile forces in the mature megakaryocyte which allows for the protrusion of proplatelets, an effect also seen in inhibition of myosin IIa (48). However, this effect may also be related to observed changes in microtubule stability which could alter motor protein interaction with microtubules facilitating proplatelet extension (49). Intriguingly, platelet counts are normal in the mDia1 knockout mouse (Thomas, Unpublished data) indicating a possible difference between human and mouse cells, or some compensatory mechanism in the knockout. As indicated above, the mDia1 knockout platelets are increased in size (Thomas, Unpublished data) suggesting that there is a defect in proplatelet formation/release when mDia1 is absent. In addition, the knockdown experiments performed by Pan et al. were done after megakaryocyte differentiation, and so, the effect of reduced mDia1 expression on human megakaryocyte development was not studied.
Related Knowledge Centers
- Cytoplasm
- Flagellum
- Hydrolysis
- Kinesin
- Protein
- Proton Pump
- Vesicle
- Active Transport
- Molecular Motor
- Adenosine Triphosphate