Inferring the origins of state-dependent courtship traits

We examine a simple model of state-dependent (indicator) traits that focuses on their evolutionary origins as courtship signals. A necessary condition for the initial evolution of signals was found: the marginal female preference for minimal traits must exceed a certain threshold, where that threshold is proportional to the marginal male fitness costs for minimal traits. We interpret a positive threshold as implying a need for preexisting sensory bias in order to overcome the threshold if indicator signals are to start to evolve. We extend the model to allow for the possibility that signal costs and female preferences may vary over evolutionary time. If there is independent information on the way that signaling costs have evolved, then one may use measurements of contemporary female preferences to make inferences concerning the presence of the ancestral threshold. It is the marginal female preferences for minimal male traits that are important, whereas reconstructing ancestral origins from measurement of average size signals is not informative. Our analyses suggest two foci for future studies: measurement of the marginal response of contemporary females to minimal male signals and reconstruction of how signaling costs have changed over evolutionary time.     

Synthesis and protein conjugation studies of vitamin K analogues

Two vitamin K analogues bearing a carboxylic acid side chain (9a and its deuterated analogue 9b) were each synthesised in six steps from commercially available menadione. Analogue 9b was conjugated to lysozyme and bovine serum albumin (BSA) using EDCI/HOBT and by prior formation of its activated succinimidyl ester 11. Quantification of the thus formed conjugates by ESMS and LC-MS revealed that the number of equivalents of the analogue used in the couplings systematically controls the number of analogues that conjugate to the protein.     

Clathrin interactions with C-terminal regions of the yeast AP-1 beta and gamma subunits are important for AP-1 association with clathrin coats

Heterotetrameric adaptor (AP) complexes are thought to coordinate cargo recruitment and clathrin assembly during clathrin-coated vesicle biogenesis. We have identified, and characterized the physiological significance of clathrin-binding activities in the two large subunits of the AP-1 complex in Saccharomyces cerevisiae . Using GST-fusion chromatography, two clathrin-binding sites were defined in the β1 subunit that match consensus clathrin-binding sequences in other mammalian and yeast clathrin-binding proteins. Clathrin interactions were also identified with the C-terminal region of the γ subunit. When introduced into chromosomal genes, point mutations in the β1 clathrin-binding motifs, or deletion of the γ C-terminal region, reduced association of AP-1 with clathrin in coimmunoprecipitation assays. The β1 mutations or the γ truncation individually produced minor effects on AP-1 distribution by subcellular fractionation. However, when β1 and γ mutations were combined, severe defects were observed in AP-1 association with membranes and incorporation into clathrin-coated vesicles. The combination of subunit mutations accentuated growth and α-factor pheromone maturation defects in chc1-ts cells, though not to the extent caused by complete loss of AP-1 activity. Our results suggest that both the β1 and γ subunits contribute interactions with clathrin that are important for stable assembly of AP-1 complexes into clathrin coats in vivo .     

Endogenous and exogenous Na-K-Cl cotransporter expression in a low K-resistant mutant MDCK cell line

A low K-resistant mutantMadin-Darby canine kidney (MDCK) cell line, LK-C1, has been shownpreviously to lack functional Na-K-Cl cotransporter (NKCC) activity,indicating that it may be a useful NKCC "knockout" cell line forstructure-function studies. Using immunological probes, we firstcharacterized the defect in the endogenous NKCC protein of the LK-C1cells and then fully restored NKCC activity in these cells by stablyexpressing the human secretory NKCC1 protein (hNKCC1). The endogenousNKCC protein of the LK-C1 cells was expressed at significantly lowerlevels than in wild-type MDCK cells and was not properly glycosylated.This latter finding indicated that the lack of functional NKCC activityin the LK-C1 cells may be due to the inability to process the proteinto the plasma membrane. In contrast, exogenously expressed hNKCC1protein was properly processed and fully functional at the plasmamembrane. Significantly, the exogenous hNKCC1 protein was regulated ina manner similar to the protein in native secretory cells as it wasrobustly activated by cell shrinkage, calyculin A, and low-Cl incubation. Furthermore, when the LK-C1 cells formed an epithelium onpermeable supports, the exogenous hNKCC1 protein was properly polarizedand functional at the basolateral membrane. The low levels ofendogenous NKCC protein expression, the absence of any endogenous NKCCtransport activity, and the ability to form a polarized epitheliumindicate that the LK-C1 cells offer an excellent expression system withwhich to study the molecular physiology of the cation Cl cotransporters.

     

Elimination of Fc receptor-dependent effector functions of a modified IgG4 monoclonal antibody to human CD4

Several CD4 mAbs have entered the clinic for the treatment of autoimmune diseases or transplant rejection. Most of these mAbs caused CD4 cell depletion, and some were murine mAbs which were further hampered by human anti-mouse Ab responses. To obviate these concerns, a primatized CD4 mAb, clenoliximab, was generated by fusing the V domains of a cynomolgus macaque mAb to human constant regions. The heavy chain constant region is a modified IgG4 containing two single residue substitutions designed to ablate residual Fc receptor binding activity and to stabilize heavy chain dimer formation. This study compares and contrasts the in vitro properties of clenoliximab with its matched IgG1 derivative, keliximab, which shares the same variable regions. Both mAbs show potent inhibition of in vitro T cell responses, lack of binding to complement component C1q, and inability to mediate complement-dependent cytotoxicity. However, clenoliximab shows markedly reduced binding to Fc receptors and therefore does not mediate Ab-dependent cell-mediated cytotoxicity or modulation/loss of CD4 from the surface of T cells, except in the presence of rheumatoid factor or activated monocytes. Thus, clenoliximab retains the key immunomodulatory attributes of keliximab without the liability of strong Fcgamma receptor binding. In initial clinical trials, these properties have translated to a reduced incidence of CD4+ T cell depletion.