A proposed structure for transmembrane segment 7 of G protein-coupled receptors incorporating an asn-Pro/Asp-Pro motif.

Transmembrane segment (TMS) 7 has been shown to play an important role in the signal transduction function of G-protein-coupled receptors (GPCRs). Although transmembrane segments are most likely to adopt a helical structure, results from a variety of experimental studies involving TMS 7 are inconsistent with it being an ideal alpha-helix. Using results from a search of the structure database and extensive simulated annealing Monte Carlo runs with the new Conformational Memories method, we have identified the conserved (N/D)PxxY region of TMS 7 as the major determinant for deviation of TMS 7 from ideal helicity. The perturbation consists of an Asx turn and a flexible "hinge" region. The Conformational Memories procedure yielded a model structure of TMS 7 which, unlike an ideal alpha-helix, is capable of accommodating all of the experimentally derived geometrical criteria for the interactions of TMS 7 in the transmembrane bundle of GPCRs. In the context of the entire structure of a transmembrane bundle model for the 5HT2a receptor, the specific perturbation of TMS 7 by the NP sequence suggests a structural hypothesis for the pattern of amino acid conservation observed in TMS 1, 2, and 7 of GPCRs. The structure resulting from the incorporation of the (N/D)P motif satisfies fully the H-bonding capabilities of the 100% conserved polar residues in these TMSs, in agreement with results from mutagenesis experiments. The flexibility introduced by the specific structural perturbation produced by the (NP/DP) motif in TMS 7 is proposed to have a significant role in receptor activation.     

Mammalian p55CDC Mediates Association of the Spindle Checkpoint Protein Mad2 with the Cyclosome/Anaphase-promoting Complex, and is Involved in Regulating Anaphase Onset and Late Mitotic Events

We have investigated the function of p55CDC, a mammalian protein related to Cdc20 and Hct1/Cdh1 in Saccharomyces cerevisiae, and Fizzy and Fizzy-related in Drosophila. Immunofluorescence studies and expression of a p55CDC-GFP chimera demonstrate that p55CDC is concentrated at the kinetochores in M phase cells from late prophase to telophase. Some p55CDC is also associated with the spindle microtubules and spindle poles, and some is diffuse in the cytoplasm. At anaphase, the concentration of p55CDC at the kinetochores gradually diminishes, and is gone by late telophase. In extracts prepared from M phase, but not from interphase HeLa cells, p55CDC coimmunoprecipitates with three important elements of the M phase checkpoint machinery: Cdc27, Cdc16, and Mad2. p55CDC is required for binding Mad2 with the Cdc27 and Cdc16. Thus, it is likely that p55CDC mediates the association of Mad2 with the cyclosome/anaphase-promoting complex. Microinjection of anti-p55CDC antibody into mitotic mammalian cells induces arrest or delay at metaphase, and impairs progression of late mitotic events. These studies suggest that mammalian p55CDC may be part of a regulatory and targeting complex for the anaphase-promoting complex.     

Taxol-induced apoptosis in human SKOV3 ovarian and MCF7 breast carcinoma cells is caspase-3 and caspase-9 independent

Taxol is used in chemotherapy regimens against breast and ovarian cancer. Treatment of tumor model cell lines with taxol induces apoptosis, but exact mechanism is not sufficiently understood. Our results demonstrate that in response to taxol, various cell types differentially utilize distinct apoptotic pathways. Using MCF7 breast carcinoma cells transfected with caspase-3 gene, we showed that taxol-induced apoptosis occurred in the absence of caspase-3 and caspase-9 activation. Similar results were obtained with ovarian SKOV3 carcinoma cells, expressing high level of endogenous caspase-3. In contrast, staurosporine-induced apoptosis in these cells was accompanied by proteolytic cleavage of pro-caspase-3 and induction of caspase-3 enzymatic activity. The effect of taxol appears to be cell type-specific, since taxol-induced apoptosis in leukemia U937 cells involved caspase-3 activation step. We conclude that a unique caspase-3 and caspase-9 independent pathway is elicited by taxol to induce apoptosis in human ovarian and breast cancinoma cells.     

In vitro cultivation of Dipetalonema viteae third-stage larvae: evaluation of culture media, serum, and other supplements

Third-stage larvae of Dipetalonema viteae obtained from the tick vector developed to the fourth stage in several cell-free culture systems. Survival and development of larvae in a number of commercially available cell culture media, supplemented with serum and other defined and undefined components, were compared. All cultures were gassed with 5% carbon dioxide in nitrogen. Best survival, growth and development were obtained in stationary cultures containing 1:1 (v/v) mixtures of NCTC 135, either RPMI 1640 or Iscove's Modified Dulbecco's Medium, and a supplement of 20% non-heat-inactivated fetal bovine serum. The importance of the medium composition and physical environment of the culture system, for the survival, growth and development of D. viteae was demonstrated.     

Conformational rearrangements to the intracellular open states of the LeuT and ApcT transporters are modulated by common mechanisms

Recent crystallographic studies revealed that five transporter families without much sequence similarities among them have similar structure folds to LeuT, a bacterial neurotransmitter:sodium symporter homolog. The LeuT fold is characterized by an internal twofold structural pseudosymmetry. The transport cycle of some members of each of these families is dependent on a sodium gradient across the membrane, whereas in some others the role of sodium is mimicked by proton. We report on the identification of common structure-dynamics elements of the transporters with LeuT fold, which are recognizable in the conformational transitions related to function. The findings from comparative computational modeling and simulation studies of LeuT, and ApcT from the amino acid-polyamine-organocation transporter family define the intramolecular mechanisms by which Na⁺ binding couples to the transport process, and single out the lead/active role of TM1a in the transition to inward-open conformation. These mechanistic insights are derived in the context of collaborative investigations of LeuT dynamics with both single-molecule fluorescence and simulations that have produced excellent agreement of the dynamic details, and are found to be generalizable across the transporter families and to transcend sequence and motif similarities.     

Microbiological and Pharmacological Behavior of 7-Chlorolincomycin

Replacement of the 7-(R) hydroxyl group of lincomycin by a 7-chloro-substituent produced a compound with greater in vitro activity than the parent. Laboratory studies of this compound showed it to be highly active against all of the following strains of gram-positive organisms examined, including penicillinase- and nonpenicillinase-producing staphylococci, Diplococcus pneumoniae, Streptococcus viridans and Streptococcus pyogenes. The enterococci, as well as all the gram-negative organisms tested, with the exception of some strains of Haemophilus, were uniformly insensitive to this agent. The activity of 7-chlorolincomycin was not affected by serum or inoculum size. Resistance developed in a slow stepwise pattern. Peak levels of approximately 2 mug/ml were achieved in the serum of volunteers after ingestion of 150 mg either in the fasting state or after a meal. No untoward effects were noted. The antibiotic appears to be of potential value in the treatment of infections due to gram-positive organisms, with the exception of enterococcus.     

The modulation of growth by HMBA in PKC overproducing HT29 colon cancer cells.

To examine whether protein kinase C (PKC) plays a role in mediating growth inhibitory effects of hexamethylene bisacetamide (HMBA) we compared a control H29 colon cancer cell line to a derivative, HT29-PKC7, that overexpresses high levels of PKC beta 1. We found that although HMBA markedly inhibited the growth of the control cells, no inhibition was seen with the HT29-PKC7 cells. On the other hand the tumor promoter 12-0-tetradecanoyl-phorbol-13 acetate inhibited the growth of HT29-PKC7 cells, but no inhibition was seen with the control cells. Maximum inhibition of the growth of both cell lines was obtained by combined treatment with HMBA and TPA. These results may be relevant to the use of HMBA in combination with other agents in the therapy of specific cancers.