SB2013 L04gr5: Difference between revisions

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Emma Brower, Alexandra DePastene, Olivia Rodrigues, Julia Joseph, Alexander Berchansky, Michal Harel

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 When crystallized, VlsE forms a four molecule asymmetric unit with each molecule having slight differences in their conformation.  Although each molecule in the unit is slightly different, a single molecule of the protein consists of eleven [http://en.wikipedia.org/wiki/Alpha_helices α-helices] and four short [http://en.wikipedia.org/wiki/Beta_strand β-strands].  Helices α1 (aa 306-341), α2 (aa 68-87), α3 (aa 114-139), and α11 (aa 306-341) all form the <scene name='SB2013_L04gr5/Membrane_proximal_region/1'>membrane proximal region</scene> of VlsE, while helices α4 (aa 161-176), α5 (aa 180-185), α6 (aa 195-201), α7 (aa 213-224), α8 (aa 228-239), α9 (aa 255-260) and α10 (aa 277-289) form the primary region of the <scene name='SB2013_L04gr5/Membrane_distal_region/2'>membrane distal region</scene> of the protein.  The four short β-strands each consist of 3 amino acids and can also be located in the membrane distal region <ref name="Eicken" />.
-Covering the membrane distal part of VlsE are connecting loop regions, which lack secondary structure and have different conformations in each of the molecules.  Helices α3 through α10 form the invariable regions and are attached by the connecting loops that are classified as the variable regions.  Although VlsE crystallizes into an asymmetrical unit, it appears primarily as monomeric in solution.  Because the interface between VlsE molecules in the crystal structure buries approximately 13% of the accessible surface area of the monomers, Eicken et al.suggest that there is a possibility of VlsE existing as a [http://en.wikipedia.org/wiki/Protein_dimer dimer] when in its natural state (Figure 2)<ref name="Eicken" />. <scene name='SB2013_L04gr5/Reset_button/1'>Reset</scene>
+Covering the membrane distal part of VlsE are connecting loop regions, which lack secondary structure and have different conformations in each of the molecules.  Helices α3 through α10 form the invariable regions and are attached by the connecting loops that are classified as the variable regions.  Although VlsE crystallizes into an asymmetrical unit, it appears primarily as monomeric in solution.  Because the interface between VlsE molecules in the crystal structure buries approximately 13% of the accessible surface area of the monomers, research suggests that there is a possibility of VlsE existing as a [http://en.wikipedia.org/wiki/Protein_dimer dimer] when in its natural state (Figure 2)<ref name="Eicken" />. <scene name='SB2013_L04gr5/Reset_button/1'>Reset</scene>
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 Figure 2 shows the possible dimerization of VlsE.
 =Antigenic Variation=
 Antigenic variation is the process by which an organism is able to evade its host’s immune system.  The antigenic variation that occurs in VlsE uses a complex genetic conversion mechanism that is seen to be concentrated in the VRs. The complex genetic system for VlsE is located near the right telomere on a 28-kb linear plasmid (lp28-1) in strains of ''B. burgdorferi''.  This [http://en.wikipedia.org/wiki/Locus_%28genetics%29 locus] has been shown to be a crucial element for the persistence and virulence of Lyme disease <ref name="Bankhead and Chaconas" />.  The ''vls'' antigenic variation locus consists of a ''vls'' expression site (''vlsE'') and 15 silent vls cassettes that reside just upstream of the site.  The ''vlsE'' cassette region, which is the variable domain and does not include the invariable amino or carboxyl termini, has approximately 92% DNA sequence identity with the silent vls cassettes.  However, the silent ''vls'' cassettes lack promoter sequences and are therefore not expressed.  Throughout the course of infection, the sequences for the flanking termini and the silent ''vls'' cassettes are conserved while the vlsE sequence is recombined.  This suggests that the genetic variation mechanism occurs by copying segments of the 15 silent vls cassettes and completely replacing corresponding segments of ''vlsE'' sequences.  The resulting differences are centralized in the highly variable regions of the ''vls'' cassettes.  This allows for the constant evolution of the VR structures and evades the antibodies of the host immune system<ref name="Zhang and Norris" />.