In order to address the dire need for new antibiotics to treat specific strains of drug resistant Gram-negative bacterial infections, a mixed ligand analog of the natural Acinetobacter baumannii selective siderophore, fimsbactin, was coupled to daptomycin, a Gram-positive only antibiotic. The resulting conjugate 11 has potent activity against multidrug resistant strains of A. baumannii both in vitro and in vivo. The study also indicates that conjugation of siderophores to "drugs" that are much larger than the siderophore (iron transport agent) itself facilitates active uptake that circumvents the normal permeability problems in Gram-negative bacteria. The results demonstrate the ability to extend activity of a normally Gram-positive only antibiotic to create a potent and targeted Gram-negative antibiotic using a bacterial iron transport based sideromycin Trojan horse strategy.

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Abstract. Myosin II purified from mammalian nonmuscle cells is phosphorylated on the 20-kD light chain subunit (MLC2o) by the Cat+/calmodulin-dependent enzyme myosin light chain kinase (MLCK) . The importance of MLC2o phosphorylation in regulating cell motility was investigated by introducing either antibodies to MLCK (MK-Ab) or a Cat+/calmodulin-independent, constitutively active form of MLCK (MK -) into macrophages . The effects of these proteins on cell motility were then determined using a quantitative chemotaxis assay. Chemotaxis is significantly diminished in macrophages containing MKAb compared to macrophages containing control antibodies . Moreover, there is an C ELLULAR locomotion by mammalian cells is essential for embryogenesis, cell-mediated killing (4), and the formation of metastatic colonies by cancer cells. Cell motility is a complex process that requires the coordinated regulation and the interaction of numerous reactions. ATP hydrolysis by actin and myosin II and myosin II polymerization/depolymerization are thought to be among the reactions involved in mediating translational motility (2, 23) . In mammalian nonmuscle cells, both ATP hydrolysis (3,30,31) and filament formation (1Q 27) by myosin II are regulated by phosphorylation of the 20-kD light chain of myosin (MLC2o)' by myosin light chain kinase (MLCK) (2) . Therefore, MLCK and MLC20 phosphorylation are thought to play critical roles in regulating cell motility.However, the role of filamentous myosin (myosin II) in cell motility is unclear. Experiments on the slime mold Dictyostelium discoideum have questioned the importance of filamentous myosin in cell motility (14,22) . Dictyostelium contains two myosins designated myosin I and myosin II (24) . Myosin I is a single-headed myosin with a short heavy chain that does not form filaments (24) . Myosin I associates with lipids (1) and has been localized in the leading edges of lamellipodia of migrating Dictyostelium ameba (17 inverse relationship between the number of cells that migrate and the amount of MKAb introduced into cells . Interestingly, there is also an inverse relationship between the number of cells that migrate and the amount of MK-introduced into cells. Other experiments demonstrated that MKAb decreased intracellular MLC 20 phosphorylation while MK-increased MLC2o phosphorylation . MK-also increased the amount of myosin associated with the cytoskeleton . These data demonstrate that the regulation of MLCK is an important aspect of cell motility and suggest that MLC2o phosphorylation must be maintained within narrow limits during translational motility by mammalian cells.II is similar to mammalian muscle and nonmuscle myosins in that it has two globular heads, a coiled-coiled tail, and an ability to form filaments . In contrast to mammalian nonmuscle and smooth muscle myosin II, ATP hydrolysis and filament formation by Dictyostelium myosin II are regulated by both heavy chain and light chain phosphorylation (24) . Interestingly, Diciyostelium in which myosin II heavy chain expres...

bstract. Ethanol/ether soluble apoproteins, comprising 17% of the total recovered surfactant-associated proteins, were isolated from rat lung surfactant and purified by silicic acid chromatography. The protein that eluted in 4:1 chloroform/methanol accounted for >85% of protein in the ethanol/ether soluble fraction and was termed surfactant apoprotein Et (Apo Et). By sodium dodecyl sulfate polyacrylamide gel electrophoresis, this protein had an apparent molecular weight of -10,500. Apo Et was evaluated for its effect on uptake of synthetic phospholipids in liposomal form by isolated granular pneumocytes (Type II alveolar epithelial cells) in primary culture. Liposomes were prepared to approximate the phospholipid composition of the aveolar surfactant, and uptake was measured by the accumulation of the radioactively labeled dipalmitoyl phosphatidyl choline fraction. The uptake of liposomal phosphatidylcholine by cells incubated for 2 h with Apo Et was increased by 61% over control. Most of the cell-associated phospholipid uptake was resistant to treatment with trypsin, suggesting an increased internalization of liposomal material in the presence of Apo Et. The effect of Apo Et on uptake was concentration and time dependent and was not associated with cell damage,