A De novo Peptide from a High Throughput Peptide Library Blocks Myosin A -MTIP Complex Formation in Plasmodium falciparum.

Apicomplexan parasites, through their motor machinery, produce the required propulsive force critical for host cell-entry. The conserved components of this so-called glideosome machinery are myosin A and myosin A Tail Interacting Protein (MTIP). MTIP tethers myosin A to the inner membrane complex of the parasite through 20 amino acid-long C-terminal end of myosin A that makes direct contacts with MTIP, allowing the invasion of Plasmodium falciparum in erythrocytes. Here, we discovered through screening a peptide library, a de-novo peptide ZA1 that binds the myosin A tail domain. We demonstrated that ZA1 bound strongly to myosin A tail and was able to disrupt the native myosin A tail MTIP complex both in vitro and in vivo. We then showed that a shortened peptide derived from ZA1, named ZA1S, was able to bind myosin A and block parasite invasion. Overall, our study identified a novel anti-malarial peptide that could be used in combination with other antimalarials for blocking the invasion of Plasmodium falciparum.

Defects in TRPM7 channel function deregulate thrombopoiesis through altered cellular Mg(2+) homeostasis and cytoskeletal architecture.

Mg(2+) plays a vital role in platelet function, but despite implications for life-threatening conditions such as stroke or myocardial infarction, the mechanisms controlling [Mg(2+)]i in megakaryocytes (MKs) and platelets are largely unknown. Transient receptor potential melastatin-like 7 channel (TRPM7) is a ubiquitous, constitutively active cation channel with a cytosolic α-kinase domain that is critical for embryonic development and cell survival. Here we report that impaired channel function of TRPM7 in MKs causes macrothrombocytopenia in mice (Trpm7(fl/fl-Pf4Cre)) and likely in several members of a human pedigree that, in addition, suffer from atrial fibrillation. The defect in platelet biogenesis is mainly caused by cytoskeletal alterations resulting in impaired proplatelet formation by Trpm7(fl/fl-Pf4Cre) MKs, which is rescued by Mg(2+) supplementation or chemical inhibition of non-muscle myosin IIA heavy chain activity. Collectively, our findings reveal that TRPM7 dysfunction may cause macrothrombocytopenia in humans and mice.

Effects of alcohol, lithium, and homocysteine on nonmuscle myosin-II in the mouse placenta and human trophoblasts.

OBJECTIVE: Mouse embryonic exposure to alcohol, lithium, and homocysteine results in intrauterine growth restriction (IUGR) and cardiac defects. Our present study focused on the placental effects. We analyzed the hypothesis that expression of nonmuscle myosin (NMM)-II isoforms involved in cell motility, mechanosensing, and extracellular matrix assembly are altered by the 3 factors in human trophoblast (HTR8/SVneo) cells in vitro and in the mouse placenta in vivo. STUDY DESIGN: After exposure during gastrulation to alcohol, homocysteine, or lithium, ultrasonography defined embryos exhibiting abnormal placental blood flow. RESULTS: NMM-IIA/NMM-IIB are differentially expressed in trophoblasts and in mouse placental vascular endothelial cells under pathological conditions. Misexpression of NMM-IIA/NMM-IIB in the affected placentas continued stably to midgestation but can be prevented by folate and myoinositol supplementation. CONCLUSION: It is concluded that folate and myoinositol initiated early in mouse pregnancy can restore NMM-II expression, permit normal placentation/embryogenesis, and prevent IUGR induced by alcohol, lithium, and homocysteine.

Viscum album agglutinin-I induces degradation of cytoskeletal proteins in leukaemia PLB-985 cells differentiated toward neutrophils: cleavage of non-muscle myosin heavy chain-IIA by caspases.

The role of the anti-cancer agent Viscum album agglutinin-I (VAA-I) in leukaemia PLB-985 cells differentiated toward a neutrophil-like phenotype by dimethylsulphoxide (PLB-985D) has never been studied. This study investigated whether or not VAA-I can induce cytoskeletal breakdown in PLB-985D cells, as previously observed in undifferentiated PLB-985 cells. VAA-I was found to induce apoptosis in PLB-985D cells, as assessed by cytology and by degradation of gelsolin, an event known to occur via caspase-3 activation. VAA-I induced cytoskeletal breakdown based on the disruption of the F-actin network and cleavage of paxillin, vimentin and lamin B(1). In addition, we demonstrated, for the first time, that non-muscle myosin heavy chain IIA (NMHC-IIA) was cleaved by VAA-I treatment. Degradation of NMHC-IIA was reversed by the pan caspase inhibitor z-VAD-fmk in PLB-985D cells and neutrophils. However, unlike lamin B(1), no NMHC-IIA was detected on the cell surface of apoptotic neutrophils. In conclusion, PLB-985D cells responded in a similar manner to neutrophils regarding the degradation of the tested cytoskeletal. Therefore, PLB-985D cells may provide a suitable substitute for neutrophils in screening experiments, preventing extensive neutrophil cell isolation.

Trifluoperazine inhibits the MgATPase activity and in vitro motility of conventional and unconventional myosins.

Trifluoperazine, a calmodulin antagonist, has recently been shown to inhibit the MgATPase activity of scallop myosin in the absence of light chain dissociation (Patel et al. (2000) J Biol Chem 275: 4880-4888). To investigate the generality of this observation and the mechanism by which it occurs, we have examined the ability of trifluoperazine to inhibit the enzymatic properties of other conventional and unconventional myosins. We show that trifluoperazine can inhibit the actin-activated MgATPase activity of rabbit skeletal muscle myosin II heavy meromyosin (HMM), phosphorylated turkey gizzard smooth muscle myosin II HMM, phosphorylated human nonmuscle myosin IIA HMM and myosin V subfragment-1 (S1). In all cases half maximal inhibition occurred at 50-75 microM trifluoperazine while light chains (myosin II) or calmodulin (myosin V) remained associated with the heavy chains. In vitro motility of all myosins tested was completely inhibited by trifluoperazine. Chymotryptic digestion of baculovirus-expressed myosin V HMM possessing only two calmodulin binding sites yielded a minimal motor fragment with no bound calmodulin. The MgATPase of this fragment was inhibited by trifluoperazine over the same range of concentrations as the S1 fragment of myosin.