Manifold manifestations of ergotism

Vasospastic side effects leading to organic manifestations are rare in ergotamine therapy. To our knowledge, combinations of more than two signs of ergotism have rarely been described in the literature so far. We present a 65-year-old male patient who as a consequence of severe migraine had developed ergotamine abuse. He was admitted to our hospital after one week of increasing abdominal pain. During laparotomy, necrotic areas of the small intestine and the sigmoid colon were resected, which on histopathologic examination revealed severe hypertrophy of the smooth musculature of mesenteric arteries, resulting from chronic vasospasms. Postoperatively, the patient developed ischaemia of the limbs which was confirmed by angiography. Before death, the patient also showed ischaemic signs in the acrae and necrosis of the tongue.

Interactions between coiled-coil proteins: Drosophila lamin Dm0 binds to the bicaudal-D protein

In a yeast two-hybrid screen we identified an interaction between Drosophila lamin Dm0, a structural nuclear protein, and BICD, a protein involved in oocyte development. The interaction can be reconstituted in vitro and takes place between segments of both proteins predicted to form coiled coils. The affinity for lamin Dm0 of the minimal binding site on BICD is modulated in a complex fashion by other BICD segments. A point mutation, F684I, that causes the dominant, bicaudal, Bic-D phenotype inhibits lamin binding in the context of the minimal lamin-binding site, but not in a larger BICD fragment. The minimal lamin-binding site of BICD binds to a few other coiled-coil proteins, but binding to these proteins is not influenced by the F684I point mutation, suggesting that the interaction with lamin may play a role in Bic-D function. Our structural studies demonstrated that BICD is 60-70% alpha-helical, is a dimer, and consists of two parts: a thin rod-shaped part of about 32 nm, and a thicker rod-shaped part of about 26 nm. Likely, the thinner rod-shaped part of full-length BICD consists of the N-terminal half of the protein, and the lamin-binding site is located within the thicker rod-shaped part.

A tailless Drosophila lamin Dm0 fragment reveals lateral associations of dimers

An early step in nuclear lamin polymerization is the longitudinal, head-to-tail association of lamin dimers through the highly conserved end segments of their rod domains. Lamin fragments lacking the carboxy-terminal tail domain (tailless lamins) form long, thin protofilaments more readily than full-length lamins do. By morphology alone it cannot be ascertained whether tailless lamin protofilaments also arise through head-to-tail association of dimers. Here, we studied by transmission electron microscopy which types of interaction are important for formation of protofilaments by a tailless lamin fragment derived from Drosophila lamin Dm0. First, we measured the lengths of tailless lamin filaments shorter than 200 nm. Many particles were longer than one and shorter than two dimers. Second, we labeled filaments formed by tailless lamin with a Fab fragment derived from a monoclonal antibody binding to an epitope residing in the amino-terminal head domain. The pattern of Fab fragments bound to lamin filaments clearly showed that most tailless lamin dimers are not arranged in a head-to-tail fashion. Third, we mutated tailless lamin using two point mutations known to inhibit head-to-tail association of full-length lamin. Thus mutated tailless lamin still formed filaments. We interpret these data according to models involving lateral associations between dimers of cytoplasmic intermediate filament proteins, using the lengths of short tailless lamin filaments as constraints. The data also demonstrate that a segment of at most 41 amino acids of the lamin tail domain is sufficient to bring about the change of mainly lateral to mainly longitudinal assembly.

In vitro assembly of Drosophila lamin Dm0--lamin polymerization properties are conserved

Vertebrate nuclear lamins exhibit polymerization properties that are remarkably different from those of vertebrate cytoplasmic intermediate filament (IF) proteins. Notably, under conditions where vertebrate cytoplasmic IF proteins form tetramers consisting of laterally associated dimers, nuclear lamin dimers associate longitudinally into head-to-tail polymers. Also, in vitro, nuclear lamins readily form paracrystalline fibers, rather than stable 10-nm filaments. To investigate whether these properties are also shared with invertebrate nuclear lamins, we analyzed in considerable detail the polymerization behavior of recombinant full-length lamin Dm0 from the invertebrate Drosophila melanogaster. This lamin differs substantially from vertebrate lamins in its primary structure. We also analyzed lamin Dm0-derived fragments lacking either the head domain (headless), the tail domain (tailless), or both (rod). Like vertebrate lamins, full-length Drosophila lamin Dm0 assembled into head-to-tail polymers, with little or no formation of tetramers by lateral association of dimers. This longitudinal assembly was severely inhibited by deletion of the head domain. Removal of the tail domain led to increased formation of filamentous polymers. Under appropriate conditions, full-length Drosophila lamin Dm0 as well as the three lamin Dm0-derived fragments assembled into paracrystalline fibers. No steady-state condition tested yielded assembly of 10-nm filaments resembling those formed by vertebrate cytoplasmic IF proteins. These findings indicate that the in vitro assembly behavior of nuclear lamins is highly conserved but distinct from that of cytoplasmic IF proteins, thus evidencing its functional importance.

Intermediate filament protein polymerization: molecular analysis of Drosophila nuclear lamin head-to-tail binding

Polymerization of intermediate filament proteins results from interactions among several distinct binding sites on the constituent proteins. Nuclear lamin head-to-tail polymers arise from one such interaction. We studied this binding using Drosophila lamin Dm0-derived fragments containing either the NH2-terminal or COOH-terminal binding site with a combination of co-immunoprecipitation, yeast two-hybrid, analytical ultracentrifugation, and electron microscopic assays. Fragment binding and full-length lamin head-to-tail polymerization were similar to each other in morphology, buffer requirements, and inhibition after phosphorylation with cdc2 kinase. Deletion analysis localized the binding sites to the ends of the rod domain that are highly conserved among all intermediate filament proteins. Point mutants, defective in binding, were isolated. Two were identical to point mutations in specific human keratin genes known to affect keratin assembly and to cause genetic skin diseases. Results further indicate that the binding sites only function in specific sequence contexts and that binding can be modulated by elements outside the binding sites (like the cdc2 kinase phosphorylation site). Our data indicate that one type of interaction in intermediate filament protein polymerization is the longitudinal binding of dimers via the conserved end segments of the coiled-coil rod domain.