ENTH/ANTH proteins and clathrin-mediated membrane budding

The epsin N-terminal homology (ENTH) domain is an evolutionarily conserved protein module found primarily in proteins that participate in clathrin-mediated endocytosis. Structural analyses and ligand-binding studies have shown that a set of proteins previously designated as harboring an ENTH domain in fact contain a highly similar, yet unique module referred to as an AP180 N-terminal homology (ANTH) domain. ENTH and ANTH (E/ANTH) domains bind both inositol phospholipids and proteins and contribute to the nucleation and formation of clathrin coats on membranes. ENTH domains also function in the development of membrane curvature through lipid remodeling during the formation of clathrin-coated vesicles. E/ANTH-bearing proteins have recently been shown to function with adaptor protein-1 and GGA adaptors at the trans-Golgi network, which suggests that E/ANTH domains are universal components of the machinery for clathrin-mediated membrane budding

Endophilin regulates JNK activation through its interaction with the germinal center kinase-like kinase

The endophilin family of proteins function in clathrin-mediated endocytosis. Here, we have identified and cloned the rat germinal center kinase-like kinase (rGLK), a member of the GCK (germinal center kinase) family of e-Jun N-terminal kinase (JNK) activating enzymes, as a novel endophilin I-binding partner. The interaction occurs both in vitro and in cells and is mediated by the Src homology 3 domain of endophilin I and a region of rGLK containing the endophilin consensus-binding sequence PPRPPPPR. Overlay analysis of rat brain extracts demonstrates that endophilin I is a major Src homology 3 domain-binding partner for rGLK. Overexpression of full-length endophilin I activates rGLK-mediated JNK activation, whereas N- and C-terminal fragments of endophilin I block JNK activation. Thus, endophilin I appears to have a novel function in JNK activation

Connecdenn, a novel DENN domain-containing protein of neuronal clathrin-coated vesicles functioning in synaptic vesicle endocytosis

Clathrin-coated vesicles (CCVs) are responsible for the endocytosis of multiple cargo, including synaptic vesicle membranes. We now describe a new CCV protein, termed connecdenn, that contains an N-terminal DENN (differentially expressed in neoplastic versus normal cells) domain, a poorly characterized protein module found in multiple proteins of unrelated function and a C-terminal peptide motif domain harboring three distinct motifs for binding the α-ear of the clathrin adaptor protein 2 (AP-2). Connecdenn coimmunoprecipitates and partially colocalizes with AP-2, and nuclear magnetic resonance and peptide competition studies reveal that all three α-ear-binding motifs contribute to AP-2 interactions. In addition, connecdenn contains multiple Src homology 3 (SH3) domain-binding motifs and coimmunoprecipitates with the synaptic SH3 domain proteins intersectin and endophilin A1. Interestingly, connecdenn is enriched on neuronal CCVs and is present in the presynaptic compartment of neurons. Moreover, connecdenn has a uniquely stable association with CCV membranes because it resists extraction with Tris and high-salt buffers, unlike most other CCV proteins, but it is not detected on purified synaptic vesicles. Together, these observations suggest that connecdenn functions on the endocytic limb of the synaptic vesicle cycle. Accordingly, disruption of connecdenn interactions with its binding partners through overexpression of the C-terminal peptide motif domain or knock down of connecdenn through lentiviral delivery of small hairpin RNA both lead to defects in synaptic vesicle endocytosis in cultured hippocampal neurons. Thus, we identified connecdenn as a component of the endocytic machinery functioning in synaptic vesicle endocytosis, providing the first evidence of a role for a DENN domain-containing protein in endocytosis

HIP1 functions in clathrin-mediated endocytosis through binding to clathrin and adaptor protein 2

Polyglutamine expansion in huntingtin is the underlying mutation leading to neurodegeneration in Huntington disease. This mutation influences the interaction of huntingtin with different proteins, including huntingtin-interacting protein I (HIP(), in which affinity to bind to mutant huntingtin is profoundly reduced. Here we demonstrate that HIP( colocalizes with markers of clathrin-mediated endocytosis in neuronal cells and is highly enriched on clathrin-coated vesicles (CCVs) purified from brain homogenates. HIP( binds to the clathrin adaptor protein 2 (AP2) and the terminal domain of the clathrin heavy chain, predominantly through a small fragment encompassing amino acids 276-335. This region, which contains consensus clathrin- and AP2-binding sites, functions in conjunction with the coiled-coil domain to target HIP( to CCVs. Expression of various HIP1 fragments leads to a potent block of clathrin-mediated endocytosis. Our findings demonstrate that HIP1 is a novel component of the endocytic machinery

Apatite stimulates the deposition of glomalin-related soil protein in a lowbush blueberry commercial field

Many wind-sensitive and unproductive soils could benefit from increased glomalin-related soil protein (GRSP), an operationally defined soil protein pool known to improve soil quality and nutrient storage. We expect at least part of this GRSP fraction to originate from fungal biomass. Although P-rich minerals such as apatite are known to increase C allocation from plants to mycorrhizal fungi, there are no studies directly linking apatite with GRSP. We investigated the effect of apatite on GRSP deposition rates in a cultivated field of wild lowbush blueberry (Vaccinium angustifolium Aiton; Vaccinium myrtilloides Michx.) in the Saguenay‒Lac-Saint-Jean region of Quebec (Canada). A field incubation technique (145 days) using sterilized porous sand bags (50 µm pores) was used to measure in situ easily extractable GRSP (EE-GRSP) deposition rates from bags with (n = 10) and without (n = 10) apatite. Half of the bags (n = 10) were also soaked in Proline® 480 SC (Bayer CropScience, Calgary, Alberta, Canada) (Prothioconazole) to determine if EE-GRSP deposition rates were affected by this commonly applied fungicide. Our results indicated that adding apatite into sand bags significantly increased (+70%) EE-GRSP deposition rates, whereas soaking the bags in fungicide had no significant effect. Although the direct linkage between GRSP and lowbush blueberry plants remains to be detailed, our study reports for the first time GRSP concentrations from lowbush blueberry soils. Implications of these findings are discussed

Huntingtin Interacting Protein 1 (HIP1) regulates clathrin assembly through direct binding to the regulatory region of the clathrin light chain

Huntingtin interacting protein 1 (HIP1) is a component of clathrin coats. We previously demonstrated that HIP1 promotes clathrin assembly through its central helical domain, which binds directly to clathrin light chains (CLCs). To better understand the relationship between CLC binding and clathrin assembly we sought to dissect this interaction. Using C-terminal deletion constructs of the HIP1 helical domain, we identified a region between residues 450 and 456 that is required for CLC binding. Within this region, point mutations showed the importance of residues Leu-451, Leu-452, and Arg-453. Mutants that fail to bind CLC are unable to promote clathrin assembly in vitro but still mediate HIP1 homodimerization and heterodimerization with the family member HIP12/HIP1R. Moreover, HIP1 binding to CLC is necessary for HIP1 targeting to clathrin-coated pits and clathrin-coated vesicles. Interestingly, HIP1 binds to a highly conserved region of CLC previously demonstrated to regulate clathrin assembly. These results suggest a role for HIP1/CLC interactions in the regulation of clathrin assembly

HIP1 and HIP12 display differential binding to F-actin, AP2, and clathrin : identification of a novel interaction with clathrin light chain

Huntingtin-interacting protein 1 (HIP1) and HIP12 are orthologues of Sla2p, a yeast protein with essential functions in endocytosis and regulation of the actin cytoskeleton. We now report that HIP1 and HIP12 are major components of the clathrin coat that interact but differ in their ability to bind clathrin and the clathrin adaptor AP2. HIP1 contains a clathrin-box and AP2 consensus-binding sites that display high affinity binding to the terminal domain of the clathrin heavy chain and the ear domain of the AP2 alpha subunit, respectively. These consensus sites are poorly conserved in HIP12 and correspondingly, HIP12 does not bind to AP2 nor does it demonstrate high affinity clathrin binding. Moreover, HIP12 co-sediments with F-actin in contrast to HIP1, which exhibits no interaction with actin in vitro. Despite these differences, both proteins efficiently stimulate clathrin assembly through their central helical domain. Interestingly, in both HIP1 and HIP12, this domain binds directly to the clathrin light chain. Our data suggest that HIP1 and HIP12 play related yet distinct functional roles in clathrin-mediated endocytosis

Reduction in keratin aggregates in epidermolysis bullosa simplex keratinocytes after pretreatment with trimethylamine N-oxide

Epidermolysis bullosa simplex (EBS) is a dominantly inherited skin disease caused by mutations in the keratin 5 (KRT5) or KRT14 genes 1. Some reports suggested that fever and/or hot weather may exacerbate EBS phenotype 2. Effective EBS therapies are still lacking. Molecular chaperones are proteins whose main function is to promote the correct folding of polypeptides (s1). Molecules such as trimethylamine N-oxide (TMAO) and sodium 4-phenylbutyrate (4-PBA) act as chemical chaperones (s2) with protein folding and stabilization activities (s3, s4, s5). Treatment of affected epidermal cells by chemical chaperones to correct the misfolded and aggregated keratins that characterize EBS seems a viable therapeutic option 3. Furthermore, the type I keratins K16 and K17 polymerize with K5, and upregulation of these proteins could replace the mutant K14 in the heterodimer and improve disease pathology (s6). Hence, chemical chaperones which can reduce keratin aggregates formation and upregulate K16 and K17 in EBS-affected cells would be ideal therapeutic candidates for EBS

Gene expression analysis of epidermolysis bullosa simplex with mottled pigmentation

Epidermolysis bullosa simplex with mottled pigmentation (EBS-MP) is a subtype of epidermolysis bullosa simplex first reported in 1979. The disease has its onset in early childhood and manifests with either much localized skin blistering, resembling the Weber-Cockayne subtype of EBS, or with more extensive bulla formation as seen in the Koebner subtype of EBS. Associated features include palmoplantar keratoderma and reticular hyperpigmentation unrelated to the blistering

Mutant huntingtin impairs axonal trafficking in mammalian neurons in vivo and in vitro

Recent data in invertebrates demonstrated that huntingtin (htt) is essential for fast axonal trafficking. Here, we provide direct and functional evidence that htt is involved in fast axonal trafficking in mammals. Moreover, expression of full-length mutant htt (mhtt) impairs vesicular and mitochondrial trafficking in mammalian neurons in vitro and in whole animals in vivo. Particularly, mitochondria become progressively immobilized and stop more frequently in neurons from transgenic animals. These defects occurred early in development prior to the onset of measurable neurological or mitochondrial abnormalities. Consistent with a progressive loss of function, wild-type htt, trafficking motors, and mitochondrial components were selectively sequestered by mhtt in human Huntington's disease-affected brain. Data provide a model for how loss of htt function causes toxicity; mhtt-mediated aggregation sequesters htt and components of trafficking machinery leading to loss of mitochondrial motility and eventual mitochondrial dysfunction