RESUMO
BACKGROUND: Leishmania spp. telomeres are composed of 5'-TTAGGG-3' repeats associated with proteins. We have previously identified LaRbp38 and LaRPA-1 as proteins that bind the G-rich telomeric strand. At that time, we had also partially characterized a protein: DNA complex, named LaGT1, but we could not identify its protein component. METHODS AND RESULTS: Using protein-DNA interaction and competition assays, we confirmed that LaGT1 is highly specific to the G-rich telomeric single-stranded DNA. Three protein bands, with LaGT1 activity, were isolated from affinity-purified protein extracts in-gel digested, and sequenced de novo using mass spectrometry analysis. In silico analysis of the digested peptide identified them as a putative calmodulin with sequences identical to the T. cruzi calmodulin. In the Leishmania genome, the calmodulin ortholog is present in three identical copies. We cloned and sequenced one of the gene copies, named it LCalA, and obtained the recombinant protein. Multiple sequence alignment and molecular modeling showed that LCalA shares homology to most eukaryotes calmodulin. In addition, we demonstrated that LCalA is nuclear, partially co-localizes with telomeres and binds in vivo the G-rich telomeric strand. Recombinant LCalA can bind specifically and with relative affinity to the G-rich telomeric single-strand and to a 3'G-overhang, and DNA binding is calcium dependent. CONCLUSIONS: We have described a novel candidate component of Leishmania telomeres, LCalA, a nuclear calmodulin that binds the G-rich telomeric strand with high specificity and relative affinity, in a calcium-dependent manner. GENERAL SIGNIFICANCE: LCalA is the first reported calmodulin that binds in vivo telomeric DNA.
Assuntos
Calmodulina/genética , Leishmania/genética , Leishmaniose/genética , Proteínas de Ligação a Telômeros/química , Sequência de Aminoácidos/genética , Calmodulina/química , DNA de Cadeia Simples/química , DNA de Cadeia Simples/genética , Humanos , Leishmania/patogenicidade , Leishmaniose/parasitologia , Ligação Proteica , Telômero , Proteínas de Ligação a Telômeros/genéticaRESUMO
Osteoblast cadherin (OB-cadherin, also known as cadherin-11) is a Ca(2+)-dependent homophilic cell adhesion molecule that is expressed mainly in osteoblasts. OB-cadherin is expressed in prostate cancer and may be involved in the homing of metastatic prostate cancer cells to bone. The extracellular domain of OB-cadherin may be used to inhibit the adhesion between prostate cancer cells and osteoblasts. In this report, we describe the expression of the extracellular domain of OB-cadherin as an Fc fusion protein (OB-CAD-Fc) in human embryonic kidney 293FT cells using a bicistronic retroviral vector. Coexpression of GFP and OB-CAD-Fc through the bicistronic vector permitted enrichment of OB-CAD-Fc-expressing cells by fluorescence-activated cell sorting. Recombinant OB-CAD-Fc proteins were secreted into cell medium, and about 0.85 mg of purified OB-CAD-Fc protein was purified from 1l of the conditioned medium using immobilized protein A-affinity chromatography. The purified OB-CAD-Fc was biologically active because it supported the adhesion of PC3 cells and L cells transduced with OB-cadherin. The availability of OB-CAD-Fc offers opportunities to test whether OB-CAD-Fc can be used to inhibit OB-cadherin-mediated prostate cancer bone metastasis in vivo or to generate antibodies for inhibiting the adhesion between prostate cancer cells and osteoblasts.
Assuntos
Caderinas/genética , Vetores Genéticos/metabolismo , Fragmentos Fc das Imunoglobulinas/biossíntese , Proteínas Recombinantes de Fusão/biossíntese , Retroviridae/metabolismo , Western Blotting , Adesão Celular/fisiologia , Linhagem Celular , Cromatografia de Afinidade/métodos , Meios de Cultivo Condicionados/química , Meios de Cultivo Condicionados/metabolismo , Eletroforese em Gel de Poliacrilamida/métodos , Vetores Genéticos/genética , Humanos , Fragmentos Fc das Imunoglobulinas/química , Fragmentos Fc das Imunoglobulinas/genética , Rim/citologia , Rim/metabolismo , Estrutura Terciária de Proteína , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Retroviridae/genética , Fatores de TempoRESUMO
Studies of telomere structure and maintenance in trypanosomatids have provided insights into the evolutionary origin and conservation of some telomeric components shared by trypanosomes and vertebrates. For example, trypanosomatid telomeres are maintained by telomerase and consist of the canonical TTAGGG repeats, which in Trypanosoma brucei can form telomeric loops (t-loops). However, the telomeric chromatin of trypanosomatids is composed of organism-specific proteins and other proteins that share little sequence similarity with their vertebrate counterparts. Because telomere maintenance mechanisms are essential for genome stability, we propose that the particular features shown by the trypanosome telomeric chromatin hold the key for the design of antiparasitic drugs.
Assuntos
DNA de Protozoário/química , DNA de Protozoário/genética , Evolução Molecular , Telômero , Trypanosomatina/química , Trypanosomatina/genética , Animais , Especificidade da Espécie , Trypanosoma brucei brucei/química , Trypanosoma brucei brucei/genéticaRESUMO
Different species of Leishmania can cause a variety of medically important diseases, whose control and treatment are still health problems. Telomere binding proteins (TBPs) have potential as targets for anti-parasitic chemotherapy because of their importance for genome stability and cell viability. Here, we describe LaTBP1 a protein that has a Myb-like DNA-binding domain, a feature shared by most double-stranded telomeric proteins. Binding assays using full-length and truncated LaTBP1 combined with spectroscopy analysis were used to map the boundaries of the Myb-like domain near to the protein only tryptophan residue. The Myb-like domain of LaTBP1 contains a conserved hydrophobic cavity implicated in DNA-binding activity. A hypothetical model helped to visualize that it shares structural homology with domains of other Myb-containing proteins. Competition assays and chromatin immunoprecipitation confirmed the specificity of LaTBP1 for telomeric and GT-rich DNAs, suggesting that LaTBP1 is a new TBP.
Assuntos
Proteínas de Ligação a DNA/química , DNA/química , Leishmania/metabolismo , Proteínas Oncogênicas v-myb/química , Telômero/química , Sequência de Aminoácidos , Animais , Sítios de Ligação , Dados de Sequência Molecular , Ligação Proteica , Estrutura Terciária de ProteínaRESUMO
The Leishmania amazonensis telomerase gene was cloned by a polymerase chain reaction-based strategy using primers designed from a Leishmania major sequence that shared similarities with conserved telomerase motifs. The genes from three other species were cloned for comparative purposes. A ClustalW multiple-sequence alignment demonstrated that the Leishmania telomerases show greater homology with each other than with the proteins of other kinetoplastids and eukaryotes. Characterization experiments indicated that the putative Leishmania telomerase gene was probably in single copy and located in the largest chromosomes. A single messenger ribonucleic acid transcript was found in promastigotes. Phylogenetic analysis suggested that Leishmania telomerase might represent a liaison between the oldest and the newest branches of telomerases.