Muneyoshi Ichikawa

Autoinhibition and cooperative activation mechanisms of cytoplasmic dynein

Cytoplasmic dynein is a two-headed microtubule-based motor responsible for diverse intracellular movements, including minus-end-directed transport of organelles. The motility of cargo transporters is regulated according to the presence or absence of cargo; however, it remains unclear how cytoplasmic dynein achieves such regulation. Here, using a recombinant and native dynein complex in vitro, we show that lone, single dynein molecules are in an autoinhibited state, in which the two motor heads are stacked together. In this state, dynein moves diffusively along a microtubule with only a small bias towards the minus end of the microtubule. When the two heads were physically separated by a rigid rod, the movement of dynein molecules became directed and processive. Furthermore, assembly of multiple dynein molecules on a single cargo enabled them to move unidirectionally and generate force cooperatively. We thus propose a mechanism of autonomous on–off switching of cargo transport, in which single dynein molecules in the cell are autoinhibited through intramolecular head–head stacking and become active when they assemble as a team on a cargo.

Recombinant human cytoplasmic dynein heavy chain 1 and 2: Observation of dynein-2 motor activity in vitro

DYNC2H1 (Homo sapiens) binds to DYNC2H1 (Homo sapiens) by electron microscopy (View interaction)

Axonemal dynein light chain-1 locates at the microtubule-binding domain of the γ heavy chain.

Dynein light chain 1 (LC1) of the outer arm dynein (OAD) complex associates with the microtubule-binding domain (MTBD) of γ heavy chain inside the complex. LC1 is considered to regulate the OAD activity and ciliary/flagellar motion by modulating γ MTBDs affinity to the B-tubule of the doublet microtubule in the axoneme.

Sea Lily Muscle Lacks a Troponin-Regulatory System, While It Contains Paramyosin

Troponin, a Ca2+-dependent regulator of striated muscle contraction, has been characterized in vertebrates, protochordates (amphioxus and ascidian), and many invertebrate animals that are categorized in protostomes, but it has not been detected in echinoderms, such as sea urchin and sea cucumber, members of subphylum Eleutherozoa. In this study, we examined the muscle of a species of isocrinid sea lilies, a member of subphylum Pelmatozoa, that constitute the most basal group of extant echinoderms to clarify whether troponin is lacking from the early evolution of echinoderms. Native thin filaments were released from the muscle homogenates in a relaxing buffer containing ATP and EGTA, a Ca2+-chelator, and were collected by ultra-centrifugation. Actin and tropomyosin, but not a troponin-like protein, were detected in the filament preparation. The filaments increased Mg2+-ATPase activity of rabbit skeletal muscle myosin irrespective of the presence or absence of Ca2+. The results indicate that Ca2+-sensitive factor, troponin, is lacking in the thin filaments of sea lily muscle as in those of the other echinoderms, sea urchin and sea cucumber. On the other hand, a paramyosin-like protein that is absent from chordates was detected in sea lily muscle as in the muscles of the other echinoderms and invertebrate animals of protostomes.