Heavy meromyosin (HMM) of myosin II and cofilin each binds to actin filaments cooperatively and forms clusters along the filaments, but it is unknown whether the two cooperative bindings are correlated and what physiological roles they have. Fluorescence microscopy demonstrated that HMM-GFP and cofilin-mCherry each bound cooperatively to different parts of actin filaments when they were added simultaneously in 0.2 μM ATP, indicating that the two cooperative bindings are mutually exclusive. In 0.1 mM ATP, the motor domain of myosin (S1) strongly inhibited the formation of cofilin clusters along actin filaments. Under this condition, most actin protomers were unoccupied by S1 at any given moment, suggesting that transiently bound S1 alters the structure of actin filaments cooperatively and/or persistently to inhibit cofilin binding. Consistently, cosedimentation experiments using copolymers of actin and actin-S1 fusion protein demonstrated that the fusion protein affects the neighboring actin protomers, reducing their affinity for cofilin. In reciprocal experiments, cofilin-actin fusion protein reduced the affinity of neighboring actin protomers for S1. Thus, allosteric regulation by cooperative conformational changes of actin filaments contributes to mutually exclusive cooperative binding of myosin II and cofilin to actin filaments, and presumably to the differential localization of both proteins in cells.
Dexter energy transfer (DET) of triplet electronic states is used to direct energy in photovoltaics, quench reactive singlet oxygen species in biological systems, and generate them in photodynamic therapy. However, the extent to which repeated DET between aromatic residues can lead to triplet energy migration in proteins has not been investigated. Here, we computationally describe DET rates in microtubules, actin filaments and the intermediate filament, vimentin.
Microtubule actin crosslinking factor 1 (MACF1), is a cytoskeletal protein that functions as a crosslinker between microtubules and actin filaments, with early studies expanding the role of this spectraplakin protein to the central nervous system and Wnt signaling. In the early 2000's, genetic alterations of MACF1 were identified in several cancers suggesting that this cytoskeletal crosslinker was involved in tumor development and progression, while preclinical studies provided evidence that MACF1 is a potential diagnostic and prognostic biomarker and therapeutic target in glioblastomas, a central nervous system cancer derived from astrocytes and neural progenitor stem cells. Furthermore, investigations in glioblastomas demonstrated that genetic inhibitory targeting of this spectraplakin protein alone and in combination with DNA damaging agents had synergistic antitumorigenic effects.
Wiskott-Aldrich syndrome (WAS) is a severe X-linked disorder caused by loss-of-function mutations in the WAS gene, responsible for encoding WASP, a key regulator of actin cytoskeleton in all hematopoietic cells except red blood cells. The mechanism underlying microthrombocytopenia, a distinctive feature of WAS and a major contributor to mortality, remains not fully elucidated. In this study, using different gene editing strategies, we corrected mutations in patient-derived WAS-induced pluripotent stem cell lines, generating isogeneic WAS iPSC lines.
Department of Hematology, The First Affiliated Hospital of USTC, Key Laboratory of Immune Response and Immunotherapy, Center for Advanced Interdisciplinary Science and Biomedicine of IHM, Institute of Blood and Cell Therapy and Anhui Provincial Key Laboratory of Blood Research and Applications, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China.
The engraftment of haematopoietic stem and progenitor cells (HSPCs), particularly in cord-blood transplants, remains challenging. Here we report the role of the corticotropin-releasing hormone (CRH) in enhancing the homing and engraftment of human-cord-blood HSPCs in bone marrow through mechanical remodelling. By using microfluidics, intravital two-photon imaging and long-term-engraftment assays, we show that treatment with CRH substantially enhances HSPC adhesion, motility and mechanical remodelling, ultimately leading to improved bone-marrow homing and engraftment in immunodeficient mice.
