Difference between revisions of "Kevinmcgee Week 11"

Revision as of 05:44, 12 November 2013

trypanosomatid Ecotins chymotrypsin amastins Sphingolipids PG-galactosyltransferases pseudogenes ribonuclease glycoinositol-phospholipids prenylation

Leishmania Background

1. Leishmania Major is a tropical parasite
2. Sepctrum of disease, “Leishmaniases”
   • broad term describing a flesh eating virus specific to Leishmania
   • 2 million infections in 88 countries annually
3. Have adapted to avoid host destruction
   • curing is very hard and doesn’t always work

Genome Structure and Content

1. 32,816,678 base pairs obtained
2. 36 chromosomes
   • single continuous sequence generated for each chromosome
3. 911 RNA genes
   • Organized differently in Tritryp genomes from L. Major
4. 8272 protein coding genes
5. 663 related families
   • Smaller gene families arose from gene duplication
   • Larger families have single genes at multiple locations on the gene

Genome Comparison

1. Leishmania is compared with other organisms
   • Trypanosoma Brucei
   • Trypanosoma Cruzi
   • Leishmania has many orthologs under in these genomes
2. 910 genes not orthologs
   • “Leishmania Restricted genes”
     • responsible for key metabolic differences
3. LmjF33.1740 and LmjF33.1750
   • Macrophage migration inhibition factor
     • Similar to that in humans that deals with immunity from macrophage

Significant Genetic Findings

Transcription

1. L. major genome is organized into 133 clusters of tens to hundreds of protein-coding genes on same DNA strand
2. Pollycistronic transcription initiates in both directions:
   • In divergent strand-switch regions
   • terminates within the convergent strand-switch regions
3. RNAP I, II and III were found in Trytrip
   • Very different from other eukaryotes
4. Not many other homologs of RNAP were found
5. These findings, along with the polycistronic gene organization, are consistent with posttranscriptional control mechanisms being the primary determinants of Tritryp gene expression

RNA Processing

1. Polyadenylation is determined by trans-splicing of downstream mRNA
2. Tritryp Poly (A) polymerases
   • two distinct ones with different functional roles
     • Homologs of CPF are present
     • No homologs of CstF are present except for CstF50
       • CstF50 deals with poyadenylation and transcription initiation/termination
       • reflects polycistronic transcription
3. Degredation of mRNA is important in gene expression
   • Exonucleases involved in decapping of mRNA were found.
4. All of these imply reliance on posttranscriptional control of gene expression

Translation and co-/postranslational modification

1. Translation machinery are found withing the tritryps
   • large amount of elF-4A gene
     • Implies nucleic acid binding
2. Protein Modification steps
   • phosphorylation
   • glycosylation
   • lipidation
3. Essential modifications
   • glycosylphosphatidylinositol anchor addition
   • acytlation
   • protein-protein interaction
   • Enzymes that catalyze these modifications are potential drug targets

Surface molecules

1. Surface molecules are very important in the infection process
   • lipophosphoglycan (LPG)
     • assembled in the lumen of the golgi apparatus
     • entire synthetic pathway has not been fully mapped
   • glycoinositol-phospholipids (GIPLs)
   • membrane proteophosphoglycan (PPG)
   • glycosylated GPI-anchored proteins
2. Sphingolipids are essential membrane componenets of eukaryotes
   • good drug targets

Proteolysis

1. Peptidases have already been identified as virulence factors and vaccine candidates

Implications

1. Tritryp genomes help show unique biology of Leishmania and give insight to Eukaryote evolution
   • Leishmania branched off from other eukaryotes very early on
   • Differences arose after branching off of Leishmania
2. Differences from other eukaryotes: posttranslational modification
   • polycistronic gene clusters
   • mRNA trans-splicing coupled with polyadenylation
3. Full genome provides crucial information for new therapies of Leishmaniasis
   • analysis of virulence factors
   • enzymes in metabolic pathways
   • potential vaccine candidates