Distal appendages (DAPs) are nanoscale, pinwheel-like structures protruding from the distal end of the centriole that mediate membrane docking during ciliogenesis, marking the cilia base around the ciliary gate. Here we determine a super-resolved multiplex of 16 centriole-distal-end components. Surprisingly, rather than pinwheels, intact DAPs exhibit a cone-shaped architecture with components filling the space between each pinwheel blade, a new structural element we term the distal appendage matrix (DAM). Specifically, CEP83, CEP89, SCLT1, and CEP164 form the backbone of pinwheel blades, with CEP83 confined at the root and CEP164 extending to the tip near the membrane-docking site. By contrast, FBF1 marks the distal end of the DAM near the ciliary membrane. Strikingly, unlike CEP164, which is essential for ciliogenesis, FBF1 is required for ciliary gating of transmembrane proteins, revealing DAPs as an essential component of the ciliary gate. Our findings redefine both the structure and function of DAPs.
We report the complete sequence of the 4,274,642-bp genome of Haloarcula marismortui, a halophilic archaeal isolate from the Dead Sea. The genome is organized into nine circular replicons of varying G+C compositions ranging from 54% to 62%. Comparison of the genome architectures of Halobacterium sp. NRC-1 and H. marismortui suggests a common ancestor for the two organisms and a genome of significantly reduced size in the former. Both of these halophilic archaea use the same strategy of high surface negative charge of folded proteins as means to circumvent the salting-out phenomenon in a hypersaline cytoplasm. A multitiered annotation approach, including primary sequence similarities, protein family signatures, structure prediction, and a protein function association network, has assigned putative functions for at least 58% of the 4242 predicted proteins, a far larger number than is usually achieved in most newly sequenced microorganisms. Among these assigned functions were genes encoding six opsins, 19 MCP and/or HAMP domain signal transducers, and an unusually large number of environmental response regulators-nearly five times as many as those encoded in Halobacterium sp. NRC-1-suggesting H. marismortui is significantly more physiologically capable of exploiting diverse environments. In comparing the physiologies of the two halophilic archaea, in addition to the expected extensive similarity, we discovered several differences in their metabolic strategies and physiological responses such as distinct pathways for arginine breakdown in each halophile. Finally, as expected from the larger genome, H. marismortui encodes many more functions and seems to have fewer nutritional requirements for survival than does Halobacterium sp. NRC-1.
Microbial rhodopsins, a diverse group of photoactive proteins found in Archaea, Bacteria, and Eukarya, function in photosensing and photoenergy harvesting and may have been present in the resource-limited early global environment. Four different physiological functions have been identified and characterized for nearly 5,000 retinal-binding photoreceptors, these being ion transporters that transport proton or chloride and sensory rhodopsins that mediate light-attractant and/or -repellent responses. The greatest number of rhodopsins previously observed in a single archaeon had been four. Here, we report a newly discovered sixrhodopsin system in a single archaeon, Haloarcula marismortui, which shows a more diverse absorbance spectral distribution than any previously known rhodopsin system, and, for the first time, two light-driven proton transporters that respond to the same wavelength. All six rhodopsins, the greatest number ever identified in a single archaeon, were first shown to be expressed in H. marismortui, and these were then overexpressed in Escherichia coli. The proteins were purified for absorption spectra and photocycle determination, followed by measurement of ion transportation and phototaxis. The results clearly indicate the existence of a proton transporter system with two isochromatic rhodopsins and a new type of sensory rhodopsin-like transducer in H. marismortui.Microbial rhodopsins comprise a large family of seven-transmembrane helical proteins that either mediate light-driven ion transport to harvest solar energy or serve as receptors to mediate phototaxis (13) and possibly photoadaptation (32). In archaea, four rhodopsins responding to different wavelengths of light with distinct functions in Halobacterium salinarum have been identified and characterized (20,32 The two ion-transporting rhodopsins perform light-driven outward proton transport to create a proton-electrochemical potential or inward chloride transport to maintain the osmotic and pH homeostasis of the cell. The photoactivated sensory rhodopsins, on the other hand, undergo light-triggered conformational changes to relay signals to their cognate transducers and consequently activate signaling cascades in a manner similar to that of the two-component system involved in eubacterial chemotaxis (1, 22) to control flagellum rotation and thus swimming direction. Our current understanding of microbial rhodopsins as both ion transporters and photosensory receptors has been based primarily on these four known rhodopsins.A recently completed genome project for Haloarcula marismortui (3) proposed the existence of six opsin-related genes, the greatest number ever found in a single archaeon. This proposal immediately raised three questions. (i) Are these six rhodopsins biologically expressed and functionally active? (ii) What is the maximum-absorbance-wavelength ( max ) distribution pattern of these six rhodopsins? (iii) Do the two extra rhodopsins, compared to the four in H. salinarum, perform new functions or have new features beyond those of t...
Tau tubulin kinase 2 (TTBK2) is a kinase known to phosphorylate tau and tubulin. It has recently drawn much attention due to its involvement in multiple important cellular processes. Here, we review the current understanding of TTBK2, including its sequence, structure, binding sites, phosphorylation substrates, and cellular processes involved. TTBK2 possesses a casein kinase 1 (CK1) kinase domain followed by a ~900 amino acid segment, potentially responsible for its localization and substrate recruitment. It is known to bind to CEP164, a centriolar protein, and EB1, a microtubule plus-end tracking protein. In addition to autophosphorylation, known phosphorylation substrates of TTBK2 include tau, tubulin, CEP164, CEP97, and TDP-43, a neurodegeneration-associated protein. Mutations of TTBK2 are associated with spinocerebellar ataxia type 11. In addition, TTBK2 is essential for regulating the growth of axonemal microtubules in ciliogenesis. It also plays roles in resistance of cancer target therapies and in regulating glucose and GABA transport. Reported sites of TTBK2 localization include the centriole/basal body, the midbody, and possibly the mitotic spindles. Together, TTBK2 is a multifunctional kinase involved in important cellular processes and demands augmented efforts in investigating its functions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.