Screening a Peptide Library by DSC and SAXD: Comparison with the Biological Function of the Parent Proteins

We have recently identified the membranotropic regions of the hepatitis C virus proteins E1, E2, core and p7 proteins by observing the effect of protein-derived peptide libraries on model membrane integrity. We have studied in this work the ability of selected sequences of these proteins to modulate the Lβ-Lα and Lα-HII phospholipid phase transitions as well as check the viability of using both DSC and SAXD to screen a protein-derived peptide library. We demonstrate that it is feasible to screen a library of peptides corresponding to one or several proteins by both SAXD and DSC. This methodological combination should allow the identification of essential regions of membrane-interacting proteins which might be implicated in the molecular mechanism of membrane fusion and/or budding

Transcriptomic analysis of the interaction between <it>Helianthus annuus </it>and its obligate parasite <it>Plasmopara halstedii </it>shows single nucleotide polymorphisms in CRN sequences

<p>Abstract</p> <p>Background</p> <p>Downy mildew in sunflowers (<it>Helianthus annuus </it>L.) is caused by the oomycete <it>Plasmopara halstedii </it>(Farl.) Berlese et de Toni. Despite efforts by the international community to breed mildew-resistant varieties, downy mildew remains a major threat to the sunflower crop. Very few genomic, genetic and molecular resources are currently available to study this pathogen. Using a 454 sequencing method, expressed sequence tags (EST) during the interaction between <it>H. annuus </it>and <it>P. halstedii </it>have been generated and a search was performed for sites in putative effectors to show polymorphisms between the different races of <it>P. halstedii</it>.</p> <p>Results</p> <p>A 454 pyrosequencing run of two infected sunflower samples (inbred lines XRQ and PSC8 infected with race 710 of <it>P. halstedii</it>, which exhibit incompatible and compatible interactions, respectively) generated 113,720 and 172,107 useable reads. From these reads, 44,948 contigs and singletons have been produced. A bioinformatic portal, HP, was specifically created for in-depth analysis of these clusters. Using <it>in silico </it>filtering, 405 clusters were defined as being specific to oomycetes, and 172 were defined as non-specific oomycete clusters. A subset of these two categories was checked using PCR amplification, and 86% of the tested clusters were validated. Twenty putative RXLR and CRN effectors were detected using PSI-BLAST. Using corresponding sequences from four races (100, 304, 703 and 710), 22 SNPs were detected, providing new information on pathogen polymorphisms.</p> <p>Conclusions</p> <p>This study identified a large number of genes that are expressed during <it>H. annuus/P. halstedii </it>compatible or incompatible interactions. It also reveals, for the first time, that an infection mechanism exists in <it>P. halstedii </it>similar to that in other oomycetes associated with the presence of putative RXLR and CRN effectors. SNPs discovered in CRN effector sequences were used to determine the genetic distances between the four races of <it>P. halstedii</it>. This work therefore provides valuable tools for further discoveries regarding the <it>H. annuus/P. halstedii </it>pathosystem.</p