User:Lian Liu
From Proteopedia
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| + | == Lyme Disease and OspB protein== | ||
| - | '' | + | Lyme disease is caused by the bacterial spirochete ''Borrelia burgdorferi sensu lato''. Colonization and survival of ''Borrelia burgdorferi'' within ticks and mammals is facilitated, in part, by [http://en.wikipedia.org/wiki/Lipoprotein lipoproteins]. OspB and OspA are two of the major lipoproteins present on the outer surface of the spirochete Borrelia Burgdoferi. Studies have shown that OspB is critical for the adherence of the spirochete to the gut wall of its tick vector. The free OspB structure consists of a barrel domain which might be the portion that interacts with a protein or a linear saccharide in the tick-gut (17368), promoting the attachment of spirochete on the tick gut. It’s speculated that destroying these lipoproteins will cause bacterial death of spirochetes. Some antibody Fab fragments such as H6831 and CB2 have been shown to cause bacterial lysis of spirochetes by binding to these lipoproteins in the absence of phagocytes and without [http://en.wikipedia.org/wiki/Complement_system complement], which is normally part of the immune response to bacteria. However, it is unclear how binding of H6831 or CB2 can lead directly to lysis of the bacterium. |
| + | ==Free OspB structure== | ||
| - | <Structure load=' | + | <Structure load='1p4p' size='350' frame='true' align='right' caption='Free OspB' scene = 'G14secL04Tpc3/Free_ospb_colored/1'/> |
| + | <scene name='G14secL04Tpc3/Free_ospb_colored/1'>Free OspB</scene> structure consists of twelve anti-parallel beta-strands followed by a single alpha helix. <scene name='G14secL04Tpc3/5-7_beta_strands_showing/1'>Beta-strands 5-7</scene> | ||
| + | and <scene name='G14secL04Tpc3/8-12_beta_strands_showing/1'>strands 8-12 </scene> | ||
| + | form two sheets that bend, along with the final <scene name='G14secL04Tpc3/8-12_beta_strands_showing/2'>alpha-helix</scene> | ||
| + | that comes over the top into the <scene name='G14secL04Tpc3/C-terminal_barrel_domain/4'>C-terminal barrel domain </scene> | ||
| + | . It has been shown that OspB deficient spirochetes lack the ability to bind to the tick gut<ref> http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.0030033</ref>. Further studies suggest that the structural barrel domain is what gives OspB the ability to adhere to the tick gut wall. The barrel domain cavity could serve as the binding site for an exposed protein loop, small peptide, or linear saccharide hanging off the tick gut wall<ref name="1rjl_pdb">http://www.jbc.org/content/280/17/17363.full</ref>. <scene name='G14secL04Tpc3/1-4_beta_strands_showing/1'>Beta strands 1-4 </scene> on the free OspB are cleaved when OspB is bound to antibody fragment H6831, suggesting that it’s removed by the proteolysis in the H6831-bound complex<ref name = "1rjl_pdb" />. | ||
| - | + | ==OspB complexed with H6831 Antibody Fab Fragment== | |
| + | <Structure load='1rjl' size='350' frame='true' align='right' caption= 'OspB bound to H6831' scene= 'G14secL04Tpc3/Ospb_in_complex/2'/> | ||
| + | |||
| + | <scene name='G14secL04Tpc3/Antibody_showing2/1'>Antibody Fab fragment H6831 </scene> (<scene name='G14secL04Tpc3/Heavy_chain/1'>Heavy chain</scene> and <scene name='G14secL04Tpc3/Light_chain/1'>light chain</scene>)has been shown to bind on an epitope of the <scene name='G14secL04Tpc3/Ospb_in_complex_with_heavy_and/2'>OspB protein</scene>. Once this occurs, the resulting OspB∙H6831 complex is formed and the first four beta strands of the OspB protein are proteolysed(citation). This loss is the most significant conformational change in the OspB protein itself, and all other changes are minor and appear to be related to this loss. The majority of the binding occurs on the C-terminus of OspB. The C-terminus consists of <scene name='G14secL04Tpc3/Three_major_loops2/3'>three major loops </scene> | ||
| + | that are involved in the electrostatic forces keeping the H6831 antibody bound to the OspB protein. Of these three loops, <scene name='G14secL04Tpc3/Loop_2/4'>loop 2</scene> | ||
| + | plays the most significant role in keeping the complex together. This is due to the presence of a <scene name='G14secL04Tpc3/Lysine-253/3'>lysine at residue 253</scene> | ||
| + | on this loop. This important lysine forms an ionic salt bridge with the <scene name='G14secL04Tpc3/Lysine-253_and_glu50/2'>glutamic acid at residue 50</scene> | ||
| + | on the heavy chain of the antibody Fab Fragment. Thus, formation of the complex consist of the C-terminus of the OspB protein coming into contact with the variable regions of the H6831 antibody Fab fragment and the lysine-253 wedging between the two <scene name='G14secL04Tpc3/Lysine-253_glu50_tyr_and_trp/2'>aromatic residues</scene> | ||
| + | (tryptophan-33 and tyrosine-101) and salt bridging with the glu-50 on the heavy chain of the antibody. Studies show that other bacterial strains having a cysteine, glycine, glutamic acid, or threonine in place of Lys-253 demonstrate resistance to the bactericidal effects of H6831 and also less binding affinity for the antibody Fab fragment (citation needed). This bolsters how important the Lys-253 is in the binding between the OspB protein and the antibody. After the complex is formed and the first four beta strands are cleaved off, a relic of this loss is a single <scene name='G14secL04Tpc3/Freely_floating_beta_strand/2'>freely floating beta strand</scene> on the N-terminus of the protein. This beta strand plays a role in the formation of dimers of OspB∙H6831 complex(citation). Although the second loop bearing the lysine is very important, the other loops certainly contribute to the bonding between OspB and the antibody fab fragment. For example, a <scene name='G14secL04Tpc3/Threonine_and_light_chain/1'>threonine</scene> | ||
| + | at residue 276 on another loop interacts with residues on the light chain of the antibody fragment. | ||
| - | <scene name='colorGroup'>N to C terminus</scene> | ||
| - | + | ==Transmission of Spirochete== | |
| - | + | ||
| - | + | ||
| - | + | Selective expression of these outer surface proteins are important for the colonization and persistence within the tick vector. | |
| - | + | It was observed that after entry into the ticks, B. burgdorferi replicates and persists within the gut, then during a subsequent blood meal, migrates through the vector and is transmitted to a new host. Other studies show that the expression of B. burgdorferi OspA and OspB is immediately turned on when the spirochetes enter and reside within the arthropod vector. However, during transmission from the arthropod vector to a vertebrate host, expression of B. burgdorferi are downregulate. Since OspA and OspB are critical for the adherence of the spirochete to the mid-gut of the tick, if this protein is down- regulated or expressed less, then it will attach less to the mid-gut of the tick and as a result be more likely to be excreted in some way into the host on which the tick is feeding. | |
| - | + | ==References== | |
| - | + | <references /> | |
Revision as of 16:19, 15 August 2012
Contents |
Lyme Disease and OspB protein
Lyme disease is caused by the bacterial spirochete Borrelia burgdorferi sensu lato. Colonization and survival of Borrelia burgdorferi within ticks and mammals is facilitated, in part, by lipoproteins. OspB and OspA are two of the major lipoproteins present on the outer surface of the spirochete Borrelia Burgdoferi. Studies have shown that OspB is critical for the adherence of the spirochete to the gut wall of its tick vector. The free OspB structure consists of a barrel domain which might be the portion that interacts with a protein or a linear saccharide in the tick-gut (17368), promoting the attachment of spirochete on the tick gut. It’s speculated that destroying these lipoproteins will cause bacterial death of spirochetes. Some antibody Fab fragments such as H6831 and CB2 have been shown to cause bacterial lysis of spirochetes by binding to these lipoproteins in the absence of phagocytes and without complement, which is normally part of the immune response to bacteria. However, it is unclear how binding of H6831 or CB2 can lead directly to lysis of the bacterium.
Free OspB structure
|
structure consists of twelve anti-parallel beta-strands followed by a single alpha helix. and form two sheets that bend, along with the final that comes over the top into the . It has been shown that OspB deficient spirochetes lack the ability to bind to the tick gut[1]. Further studies suggest that the structural barrel domain is what gives OspB the ability to adhere to the tick gut wall. The barrel domain cavity could serve as the binding site for an exposed protein loop, small peptide, or linear saccharide hanging off the tick gut wall[2]. on the free OspB are cleaved when OspB is bound to antibody fragment H6831, suggesting that it’s removed by the proteolysis in the H6831-bound complex[2].
OspB complexed with H6831 Antibody Fab Fragment
|
( and )has been shown to bind on an epitope of the . Once this occurs, the resulting OspB∙H6831 complex is formed and the first four beta strands of the OspB protein are proteolysed(citation). This loss is the most significant conformational change in the OspB protein itself, and all other changes are minor and appear to be related to this loss. The majority of the binding occurs on the C-terminus of OspB. The C-terminus consists of that are involved in the electrostatic forces keeping the H6831 antibody bound to the OspB protein. Of these three loops, plays the most significant role in keeping the complex together. This is due to the presence of a on this loop. This important lysine forms an ionic salt bridge with the on the heavy chain of the antibody Fab Fragment. Thus, formation of the complex consist of the C-terminus of the OspB protein coming into contact with the variable regions of the H6831 antibody Fab fragment and the lysine-253 wedging between the two (tryptophan-33 and tyrosine-101) and salt bridging with the glu-50 on the heavy chain of the antibody. Studies show that other bacterial strains having a cysteine, glycine, glutamic acid, or threonine in place of Lys-253 demonstrate resistance to the bactericidal effects of H6831 and also less binding affinity for the antibody Fab fragment (citation needed). This bolsters how important the Lys-253 is in the binding between the OspB protein and the antibody. After the complex is formed and the first four beta strands are cleaved off, a relic of this loss is a single on the N-terminus of the protein. This beta strand plays a role in the formation of dimers of OspB∙H6831 complex(citation). Although the second loop bearing the lysine is very important, the other loops certainly contribute to the bonding between OspB and the antibody fab fragment. For example, a at residue 276 on another loop interacts with residues on the light chain of the antibody fragment.
Transmission of Spirochete
Selective expression of these outer surface proteins are important for the colonization and persistence within the tick vector. It was observed that after entry into the ticks, B. burgdorferi replicates and persists within the gut, then during a subsequent blood meal, migrates through the vector and is transmitted to a new host. Other studies show that the expression of B. burgdorferi OspA and OspB is immediately turned on when the spirochetes enter and reside within the arthropod vector. However, during transmission from the arthropod vector to a vertebrate host, expression of B. burgdorferi are downregulate. Since OspA and OspB are critical for the adherence of the spirochete to the mid-gut of the tick, if this protein is down- regulated or expressed less, then it will attach less to the mid-gut of the tick and as a result be more likely to be excreted in some way into the host on which the tick is feeding.
