The structure and assembly of the hetero-octameric BLOC-one-related complex.

BORC (BLOC-one-related complex) is a hetero-octameric complex, consisting of eight coiled-coil proteins (BORCS1-8). BORC controls lysosomal and synaptic vesicle transport and positioning by recruiting ARL8. The structural mechanisms underlying BORC assembly and ARL8 activation remain unclear.

CAMSAP3 forms dimers via its α-helix domain that directly stabilize non-centrosomal microtubule minus ends.

Microtubules are vital components of the cytoskeleton. Their plus ends are dynamic and respond to changes in cell morphology, whereas the minus ends are stable and serve a crucial role in microtubule seeding and maintaining spatial organization. In mammalian cells, the calmodulin-regulated spectrin-associated proteins (CAMSAPs), play a key role in directly regulating the dynamics of non-centrosomal microtubules minus ends.

Stiff matrix induces exosome secretion to promote tumour growth.

Tissue fibrosis and extracellular matrix (ECM) stiffening promote tumour progression. The mechanisms by which ECM regulates its contacting cells have been extensively studied. However, how stiffness influences intercellular communications in the microenvironment for tumour progression remains unknown.

Intertwined Wdr47-NTD dimer recognizes a basic-helical motif in Camsap proteins for proper central-pair microtubule formation.

Calmodulin-regulated spectrin-associated proteins (Camsaps) bind to the N-terminal domain of WD40-repeat 47 (Wdr47-NTD; featured with a LisH-CTLH motif) to properly generate axonemal central-pair microtubules (CP-MTs) for the planar beat pattern of mammalian motile multicilia. The underlying molecular mechanism, however, remains unclear. Here, we determine the structures of apo-Wdr47-NTD and Wdr47-NTD in complex with a characteristic Wdr47-binding region (WBR) from Camsap3.

The architecture of kinesin-3 KLP-6 reveals a multilevel-lockdown mechanism for autoinhibition.

Autoinhibition of kinesin-3 ensures the proper spatiotemporal control of the motor activity for intracellular transport, but the underlying mechanism remains elusive. Here, we determine the full-length structure of kinesin-3 KLP-6 in a compact self-folded state. Unexpectedly, all the internal coiled-coil segments and domains in KLP-6 cooperate to successively lock down the neck and motor domains.

Characterization of a thermostable, protease-tolerant inhibitor of α-glycosidase from carrot: A potential oral additive for treatment of diabetes.

Inhibiting α-glucosidase activity is important in controlling postprandial hyperglycemia and, thus, helping to manage type-2 diabetes mellitus (T2DM). In the present study, we purified a hypothetical protein of carrots called DCHP (Daucus Carrot hypoglycemic peptide), and their inhibitory effects on α-glucosidase, as well as related mechanisms, were investigated. The recombinant DCHP protein with a molecular weight of 8 kDa showed strong inhibitory activity against α-glycosidase and maintained good stability in solution.

Motor domain-mediated autoinhibition dictates axonal transport by the kinesin UNC-104/KIF1A.

The UNC-104/KIF1A motor is crucial for axonal transport of synaptic vesicles, but how the UNC-104/KIF1A motor is activated in vivo is not fully understood. Here, we identified point mutations located in the motor domain or the inhibitory CC1 domain, which resulted in gain-of-function alleles of unc-104 that exhibit hyperactive axonal transport and abnormal accumulation of synaptic vesicles. In contrast to the cell body localization of wild type motor, the mutant motors accumulate on neuronal processes.

CASK modulates the assembly and function of the Mint1/Munc18-1 complex to regulate insulin secretion.

Calcium/calmodulin-dependent protein serine kinase (CASK) is a key player in vesicle transport and release in neurons. However, its precise role, particularly in nonneuronal systems, is incompletely understood. We report that CASK functions as an important regulator of insulin secretion.

Multi-site-mediated entwining of the linear WIR-motif around WIPI β-propellers for autophagy.

WIPI proteins (WIPI1-4) are mammalian PROPPIN family phosphoinositide effectors essential for autophagosome biogenesis. In addition to phosphoinositides, WIPI proteins can recognize a linear WIPI-interacting-region (WIR)-motif, but the underlying mechanism is poorly understood. Here, we determine the structure of WIPI3 in complex with the WIR-peptide from ATG2A.

Multiplexed GTPase and GEF biosensor imaging enables network connectivity analysis.

Here we generate fluorescence resonance energy transfer biosensors for guanine exchange factors (GEFs) by inserting a fluorescent protein pair in a structural 'hinge' common to many GEFs. Fluorescent biosensors can map the activation of signaling molecules in space and time, but it has not been possible to quantify how different activation events affect one another or contribute to a specific cell behavior. By imaging the GEF biosensors in the same cells as red-shifted biosensors of Rho GTPases, we can apply partial correlation analysis to parse out the extent to which each GEF contributes to the activation of a specific GTPase in regulating cell movement.

Structural Conservation of the Two Phosphoinositide-Binding Sites in WIPI Proteins.

WIPI proteins are mammalian PROPPIN family members that bind to phosphoinositides and play prominent roles in autophagosome biogenesis. Two phosphoinositide-binding sites were previously described in yeast PROPPIN Hsv2 but remain to be determined in mammalian WIPI proteins. Here, we characterized four human WIPI proteins (WIPI1-4) and solved the structure of WIPI3.

YWHA/14-3-3 proteins recognize phosphorylated TFEB by a noncanonical mode for controlling TFEB cytoplasmic localization.

As a master regulator of the macroautophagy/autophagy-lysosomal pathway, TFEB (transcription factor EB) plays a prominent role in regulating neurodegenerative diseases and cancer. The transcription activity of TFEB is tightly controlled by phosphorylation and dephosphorylation. Phosphorylated S211 (p-S211) of TFEB can be recognized by YWHA/14-3-3 proteins for TFEB cytoplasmic localization.

Coiled-coil 1-mediated fastening of the neck and motor domains for kinesin-3 autoinhibition.

In kinesin-3, the coiled-coil 1 (CC1) can sequester the preceding neck coil (NC) for autoinhibition, but the underlying mechanism is poorly understood. Here, we determined the structures of the uninhibited motor domain (MD)-NC dimer and inhibited MD-NC-CC1 monomer of kinesin-3 KIF13B. In the MD-NC-CC1 monomer, CC1 is broken into two short helices that unexpectedly interact with both the NC and the MD.

Structural Delineation of the Neck Linker of Kinesin-3 for Processive Movement.

Processive kinesin motors contain a neck linker (NL) that mediates the chemo-mechanical coupling and controls the directionality and processivity. However, kinesin-3 NL remains poorly determined due to the lack of the structural information of the junction with the following neck coil (NC). Here, we determined the structure of the motor domain (MD)-NL-NC tandem of KIF13B that defines the junction between NL and NC and delineates kinesin-3 NL.

Calcium-induced structural rearrangements release autoinhibition in the Rap-GEF CalDAG-GEFI.

Platelets are recruited to sites of vascular injury, where they are activated and aggregate to form a hemostatic plug. This process requires the activation of the small GTPase Rap1B by its cognate guanine nucleotide exchange factor CalDAG-GEFI. Studies on platelet function suggest that CalDAG-GEFI activity is regulated by changes in cytosolic calcium, but the exact molecular mechanism is poorly understood.

Noncanonical Myo9b-RhoGAP Accelerates RhoA GTP Hydrolysis by a Dual-Arginine-Finger Mechanism.

The GTP hydrolysis activities of Rho GTPases are stimulated by GTPase-activating proteins (GAPs), which contain a RhoGAP domain equipped with a characteristic arginine finger and an auxiliary asparagine for catalysis. However, the auxiliary asparagine is missing in the RhoGAP domain of Myo9b (Myo9b-RhoGAP), a unique motorized RhoGAP that specifically targets RhoA for controlling cell motility. Here, we determined the structure of Myo9b-RhoGAP in complex with GDP-bound RhoA and magnesium fluoride.

A negative-feedback loop regulating ERK1/2 activation and mediated by RasGPR2 phosphorylation.

The dynamic regulation of ERK1 and -2 (ERK1/2) is required for precise signal transduction controlling cell proliferation, differentiation, and survival. However, the underlying mechanisms regulating the activation of ERK1/2 are not completely understood. In this study, we show that phosphorylation of RasGRP2, a guanine nucleotide exchange factor (GEF), inhibits its ability to activate the small GTPase Rap1 that ultimately leads to decreased activation of ERK1/2 in cells.

Coiled-Coil Domains of SUN Proteins as Intrinsic Dynamic Regulators.

SUN proteins are the core components of LINC complexes that span across the nuclear envelope for nuclear positioning and migration. SUN proteins contain at least one predicted coiled-coil domain preceding the SUN domain. Here, we found that the two coiled-coil domains (CC1 and CC2) of SUN2 exhibit distinct oligomeric states.

Structural Basis of the Differential Function of the Two C. elegans Atg8 Homologs, LGG-1 and LGG-2, in Autophagy.

Multicellular organisms have multiple homologs of the yeast ATG8 gene, but the differential roles of these homologs in autophagy during development remain largely unknown. Here we investigated structure/function relationships in the two C. elegans Atg8 homologs, LGG-1 and LGG-2.

Structural Correlation of the Neck Coil with the Coiled-coil (CC1)-Forkhead-associated (FHA) Tandem for Active Kinesin-3 KIF13A.

Processive kinesin motors often contain a coiled-coil neck that controls the directionality and processivity. However, the neck coil (NC) of kinesin-3 is too short to form a stable coiled-coil dimer. Here, we found that the coiled-coil (CC1)-forkhead-associated (FHA) tandem (that is connected to NC by Pro-390) of kinesin-3 KIF13A assembles as an extended dimer.

Myo9b is a key player in SLIT/ROBO-mediated lung tumor suppression.

Emerging evidence indicates that the neuronal guidance molecule SLIT plays a role in tumor suppression, as SLIT-encoding genes are inactivated in several types of cancer, including lung cancer; however, it is not clear how SLIT functions in lung cancer. Here, our data show that SLIT inhibits cancer cell migration by activating RhoA and that myosin 9b (Myo9b) is a ROBO-interacting protein that suppresses RhoA activity in lung cancer cells. Structural analyses revealed that the RhoGAP domain of Myo9b contains a unique patch that specifically recognizes RhoA.

Interdomain interface-mediated target recognition by the Scribble PDZ34 supramodule.

Tandem-arranged PDZ [PSD-95 (postsynaptic density-95), Dlg (discs large homologue) and ZO-1 (zonula occludens-1)] domains often form structural and functional supramodules with distinct target-binding properties. In the present study, we found that the two PDZ domains within the PDZ34 tandem of Scribble, a cell polarity regulator, tightly pack in a 'front-to-back' mode to form a compact supramodule. Although PDZ4 contains a distorted αB/βB pocket, the attachment of PDZ4 to PDZ3 generates an unexpected interdomain pocket that is adjacent to and integrates with the canonical αB/βB pocket of PDZ3 to form an expanded target-binding groove.

Activation of Rab8 guanine nucleotide exchange factor Rabin8 by ERK1/2 in response to EGF signaling.

Exocytosis is tightly regulated in many cellular processes, from neurite expansion to tumor proliferation. Rab8, a member of the Rab family of small GTPases, plays an important role in membrane trafficking from the trans-Golgi network and recycling endosomes to the plasma membrane. Rabin8 is a guanine nucleotide exchange factor (GEF) and major activator of Rab8.

Brain tumor regulates neuromuscular synapse growth and endocytosis in Drosophila by suppressing mad expression.

The precise regulation of synaptic growth is critical for the proper formation and plasticity of functional neural circuits. Identification and characterization of factors that regulate synaptic growth and function have been under intensive investigation. Here we report that brain tumor (brat), which was identified as a translational repressor in multiple biological processes, plays a crucial role at Drosophila neuromuscular junction (NMJ) synapses.