Distinct functional sites for human immunodeficiency virus type 1 and stromal cell-derived factor 1alpha on CXCR4 transmembrane helical domains

The entry of human immunodeficiency virus type 1 (HIV-1) into the cell is initiated by the interaction of the viral surface envelope protein with two cell surface components of the target cell, CD4 and a chemokine coreceptor, usually CXCR4 or CCR5. The natural ligand of CXCR4 is stromal cell-derived factor 1alpha (SDF-1alpha). Whereas the overlap between HIV-1 and SDF-1alpha functional sites on the extracellular domains of CXCR4 has been well documented, it has yet to be determined whether there are sites in the transmembrane (TM) helices of CXCR4 important for HIV-1 and/or SDF-1alpha functions, and if such sites do exist, whether they are overlapping or distinctive for the separate functions of CXCR4. For this study, by employing alanine-scanning mutagenesis, (125)I-SDF-1alpha competition binding, Ca(2+) mobilization, and cell-cell fusion assays, we found that the mutation of many CXCR4 TM residues, including Tyr(45), His(79), Asp(97), Pro(163), Trp(252), Tyr(255), Asp(262), Glu(288), His(294), and Asn(298), could selectively decrease HIV-1-mediated cell fusion but not the binding activity of SDF-1alpha. Phe(87) and Phe(292), which were involved in SDF-1alpha binding, did not play a significant role in the coreceptor activity of CXCR4, further demonstrating the disconnection between physiological and pathological activities of CXCR4 TM domains. Our data also show that four mutations of the second extracellular loop, D182A, D187A, F189A, and P191A, could reduce HIV-1 entry without impairing either ligand binding or signaling. Taken together, our first detailed characterization of the different functional roles of CXCR4 TM domains may suggest a mechanistic basis for the discovery of new selective anti-HIV agents.     

Dinuclear macrocyclic polyamine zinc(II) complexes linked with flexible spacers: synthesis, characterization, and DNA cleavage

Dinuclear macrocyclic polyamine zinc(II) complexes, which have two cyclen groups linked by flexible spacers, have been synthesized as DNA cleavage agents. The structures of these new dinuclear complexes are consistent with the data obtained from elemental analysis, MS and ¹H NMR spectroscopy. The catalytic activity of these dinuclear complexes on DNA cleavage was studied. The results showed that the dinuclear zinc(II) complexes can catalyze the cleavage of supercoiled DNA (pUC 19 plasmid DNA) (Form I) under physiological conditions to produce selectively nicked DNA (Form II).     

Morphological alterations by ectopic expression of the rice OsMADS4 gene in tobacco plants

OsMADS4, a rice MADS-box gene, is a member of the GLO/PI family that specifies the identity of petals and stamens in combination with other MADS-box genes. We report here the ectopic expression of OsMADS4 fused to the CaMV 35S promoter in tobacco plants. Transgenic plants carrying the CaMV 35S promoter::OsMADS4 construct generated mutant flowers with a mosaic carpel, in which the tissue around the nectary was elongated and the styles reduced. The fruits were distorted, but viable seeds did develop. These phenotypes mimicked those of transgenic tobacco plants that ectopically express Antirrhinum GLO. However, unlike GLO, OsMADS4 did not cause any homeotic change in the first whorl of the transgenic flowers. These results suggest that the functional role of OsMADS4 in the outer whorls has diverged from that of its dicot counterparts.     

How strong is the mutagenicity of recombination in mammals?

It is commonly believed that a high recombination rate such as that in a pseudoautosomal region (PAR) greatly increases the mutation rate because a 170-fold increase was estimated for the mouse PAR region. However, sequencing PAR and non-PAR introns of the Fxy gene in four Mus taxa, we found an increase of only twofold to fivefold. Furthermore, analyses of sequence data from human and orangutan PAR and X-linked regions and from autosomal regions showed a weak effect of recombination on mutation rate (a slope of less than 0.2% per cM/Mb), although a much stronger effect on GC content (1% to 2% per cM/Mb). Because typical recombination rates in mammals are much lower than those in PARs, the mutagenicity of recombination is weak or, at best, moderate, although its effect on GC% is much stronger. In addition, contrary to a previous study, we found no Fxy duplicate in Mus spretus.     

The C2 domain of PKCdelta is a phosphotyrosine binding domain

In eukaryotic cells, the SH2 and PTB domains mediate protein-protein interactions by recognizing phosphotyrosine residues on target proteins. Here we make the unexpected finding that the C2 domain of PKCdelta directly binds to phosphotyrosine peptides in a sequence-specific manner. We provide evidence that this domain mediates PKCdelta interaction with a Src binding glycoprotein, CDCP1. The crystal structure of the PKCdelta C2 domain in complex with an optimal phosphopeptide reveals a new mode of phosphotyrosine binding in which the phosphotyrosine moiety forms a ring-stacking interaction with a histidine residue of the C2 domain. This is also the first example of a protein Ser/Thr kinase containing a domain that binds phosphotyrosine.     

Aquaporin expression and freeze tolerance in Candida albicans

Aquaporins are members of the major intrinsic protein superfamily of integral membrane proteins which enable the transport of water, glycerol, and other solutes across membranes in various organisms. In microorganisms, the physiological role of aquaporins is not yet defined. We found a clear correlation between expression of the Candida albicans aquaporin-encoding gene AQY1 and freeze tolerance. A connection with the function for the aquaporin in the natural environment of C. albicans is, however, not obvious.     

Molecular mechanisms of the 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced inverted U-shaped dose responsiveness in anchorage independent growth and cell proliferation of human breast epithelial cells with stem cell characteristics

Although 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has a variety of carcinogenic and noncarcinogenic effects in experimental animals, its role in human carcinogenicity remain controversial. A simian virus 40-immortalized cell line from normal human breast epithelial cells with stem cells and luminal characteristics (M13SV1) was used to study whether TCDD can induce AIG positive colony formation and cause increased cell numbers in a inverted U-shaped dose–response manner. TCDD activated Akt, ERK2, and increased the expression of CYP1A1, PAI-2, IL-lb mRNA, and ERK2 protein levels. TCDD was able to increased phosphorylation and expression of ERK2 in same dose–response manner as AIG positive colony formation. Thus, TCDD induced tumorigenicity in M13SV1, possibly through the phosphorylation of ERK2 and/or Akt. Further, cDNA microarray with 7448 sequence-verified clones was used to profile various gene expression patterns after treatment of TCDD. Three clear patterns could be delineated: genes that were dose-dependently up-regulated, genes expressed in either U-shape and/or inverted U-shape. The fact that these genes are intrinsically related to breast epithelial cell proliferation and survival clearly suggests that they may be involved in the TCDD-induced breast tumorigenesis.     

High level expression, purification, and characterization of the shrimp antimicrobial peptide, Ch-penaeidin, in Pichia pastoris

Penaeidins, members of a new family of antimicrobial peptides constitutively produced and stored in the haemocytes of penaeid shrimp, display antimicrobial activity against bacteria, and fungi. Here, a DNA sequence encoding the mature Ch-penaeidin peptide was cloned into the pPIC9K vector and transformed into Pichia pastoris. The transformed cells were screened for multi-copy plasmids using increasing concentrations of G418. Positive colonies carrying chromosomal integrations of the Chp gene were identified by phenotype and PCR. When transformed cells were induced with methanol, SDS-PAGE and Western blotting revealed the production of a approximately 6100 Da recombinant CHP (rCHP) expression product. Large scale expression revealed that rCHP was produced at 108 mg/L under optimal conditions in the highest Chp-producing P. pastoris clone. The antimicrobial activities of rCHP were studied by liquid phase analysis, which revealed that rCHP exhibited activities against some Gram-negative and Gram-positive bacteria, but had a relatively low activity against some fungi. Purification of rCHP by cation exchange chromatography and subsequent automated amino acid sequencing revealed the presence of four additional amino acids (YVEF) at the N-terminus that belonged to the cleaved fusion signal peptide; these residues may account for the observed decrease in antifungal activity. Together, these observations indicate that rCHP is an effective antimicrobial peptide that can be successfully produced at high levels in the yeast, and therefore may be a potential antimicrobial candidate for practical use.