OspC and Binding

== OspC and Binding ==

<applet load='1GGQ' size='500' frame='true' align='right' caption='Outer Surface Protein C of the B. burgdorferi spirochete.' scene= />

The outer surface protein C (ospC) is a major antigen on the outer surface of the membrane of[http://en.wikipedia.org/wiki/Borrelia_burgdorferi '' B. burgdorferi''], the [http://en.wikipedia.org/wiki/Spirochete spirochete] that causes [http://en.wikipedia.org/wiki/Lyme_disease Lyme disease]. Although its main functions are largely unknown, ospC’s large degree of [http://en.wikipedia.org/wiki/Polymorphism_%28biology%29 polymorphism] allows it to be an effective tool in [http://en.wikipedia.org/wiki/Epidemiology epidemiology] and [http://en.wikipedia.org/wiki/Ecology ecology]. The different alleles coding for different types of groups of ospC’s are called ospC Major Groups (oMG’s). There are approximately 19 oMG’s, four of which—oMG’s A, B, I, and K—are virulent to humans (Kumaran et al. 2001). Research has found that infection rates of susceptible hosts to virulent oMG’s are higher where genetic variation is low due to [http://en.wikipedia.org/wiki/Population_bottleneck bottleneck effects] in certain regions of the world, such as the northeastern United States and parts of Europe (Wei-Gang et al. 2002). However, rarer oMG’s also hold a selective advantage in subsequent infections of a host, as the host’s strong secondary response would prevent infection from an oMG to which it has already been exposed (Brisson et al. 2002).

As a kidney-shaped structure with 174 amino acid residues, the ospC is a tetramer composed of two dimers. Most of the structure consists of <scene name='User:Gayatri_Setia/Workbench/Alpha_helices/2'>alpha helices</scene>, which are colored purple in the constructed model of <scene name='User:Gayatri_Setia/Workbench/Chain_a/2'>Chain A</scene>. There is only one <scene name='User:Gayatri_Setia/Workbench/Beta_sheet/1'>ß-pleated sheet</scene> on Chain A, marked in yellow.

As ospC synthesis is increased upon transfer to a host, possibly due to a temperature increase, there is a possibility of a direct interaction between the ospC and the host (Kumaran et al. 2011). There is a higher density of <scene name='User:Gayatri_Setia/Workbench/Negative_charge_distribution/1'>negatively charged amino acids</scene>—marked in red—on one side of each dimer of virulent oMG’s than there is in non-virulent oMG’s (Fig. 1), which suggests a possible binding site for ospC with positively charged host-ligands.

[[Image:Fig_1.jpg]]

Fig. 1 shows the electrostatic surface potential map of A(HB19) and B(212). HB19 is a virulent strain from oMG A, and 212 is from a non-virulent strain. (Source: Kumaran et al. 2001)