Retardation of a surface protein chimera at the cis Golgi

Antimicrobial peptides in action

Molecular dynamics simulations of the magainin MG-H2 peptide interacting with a model phospholipid membrane have been used to investigate the mechanism by which antimicrobial peptides act. Multiple copies of the peptide were randomly placed in solution close to the membrane. The peptide readily bound to the membrane, and above a certain concentration, the peptide was observed to cooperatively induce the formation of a nanometer-sized, toroidally shaped pore in the bilayer. In sharp contrast with the commonly accepted model of a toroidal pore, only one peptide was typically found near the center of the pore. The remaining peptides lay close to the edge of the pore, maintaining a predominantly parallel orientation with respect to the membrane.

Cytoplasmic dynein (ddlc1) mutations cause morphogenetic defects and apoptotic cell death in Drosophila melanogaster

We report the molecular and genetic characterization of the cytoplasmic dynein light-chain gene, ddlc1, from Drosophila melanogaster. ddlc1 encodes the first cytoplasmic dynein light chain identified, and its genetic analysis represents the first in vivo characterization of cytoplasmic dynein function in higher eucaryotes. The ddlc1 gene maps to 4E1-2 and encodes an 89-amino-acid polypeptide with a high similarity to the axonemal 8-kDa outer-arm dynein light chain from Chlamydomonas flagella. Developmental Northern (RNA) blot analysis and ovary and embryo RNA in situ hybridizations indicate that the ddlc1 gene is expressed ubiquitously. Anti-DDLC1 antibody analyses show that the DDLC1 protein is localized in the cytoplasm. P-element-induced partial-loss-of-function mutations cause pleiotropic morphogenetic defects in bristle and wing development, as well as in oogenesis, and hence result in female sterility. The morphological abnormalities found in the ovaries are always associated with a loss of cellular shape and structure, as visualized by a disorganization of the actin cytoskeleton. Total-loss-of-function mutations cause lethality. A large proportion of mutant animals degenerate during embryogenesis, and the dying cells show morphological changes characteristic of apoptosis, namely, cell and nuclear condensation and fragmentation, as well as DNA degradation. Cloning of the human homolog of the ddlc1 gene, hdlc1, demonstrates that the dynein light-chain 1 is highly conserved in flies and humans. Northern blot analysis and epitope tagging show that the hdlc1 gene is ubiquitously expressed and that the human dynein light chain 1 is localized in the cytoplasm. hdlc1 maps to 14q24.

Regulation of targeting signals in membrane proteins. [review]

Membrane proteins can contain short sequence motifs that determine their intracellular location, either by a retention or a retrieval mechanism. In both cases the targeting signal is essentially a specific binding site for other proteins that effect the localization. The folding of targeting motifs is often robust leading to a dominant effect in molecular cut and paste experiments designed to identify them. However regulation can also occur, allowing a single membrane protein to express different targeting signals at different locations in the cell. Regulation can be achieved by phosphorylation of the cytoplasmic domain leading to changes in binding affinity for effector proteins, or by masking of the targeting signal by complex formation.