User:Nathan Roy: Difference between revisions
Jump to navigation
Jump to search
Nathan Roy (talk | contribs) No edit summary |
Nathan Roy (talk | contribs) No edit summary |
||
| Line 3: | Line 3: | ||
The HIV-1 Gag protein is the major structural protein required for virus assembly. It is synthesized as a polyprotein in the cytosol of an infected cell, and contains four functional segments; MA, CA (NTD and CTD), NC, and p6. The NC region is flanked by two "spacer" segments, denoted SP1 and SP2. The polyprotein is all alpha helical, except the NC region, which is composed of two RNA interacting zinc knuckle domains. Gag is often referred to as an "assembly machine", because expression of Gag alone is sufficient to produce budding virus-like particles (VLP's), due to multimerization of roughly 2000 Gag molecules per virion. Here, we will take a closer look at the MA and CA domains, and how the structural components of these domains aid in the assembly of virus particles. <applet load='2H3F_mono1.pdb' size='300' frame='true' align='right' caption=' FIGURE 1. MA unbound to PI(4,5)P2' scene=''/> | The HIV-1 Gag protein is the major structural protein required for virus assembly. It is synthesized as a polyprotein in the cytosol of an infected cell, and contains four functional segments; MA, CA (NTD and CTD), NC, and p6. The NC region is flanked by two "spacer" segments, denoted SP1 and SP2. The polyprotein is all alpha helical, except the NC region, which is composed of two RNA interacting zinc knuckle domains. Gag is often referred to as an "assembly machine", because expression of Gag alone is sufficient to produce budding virus-like particles (VLP's), due to multimerization of roughly 2000 Gag molecules per virion. Here, we will take a closer look at the MA and CA domains, and how the structural components of these domains aid in the assembly of virus particles. <applet load='2H3F_mono1.pdb' size='300' frame='true' align='right' caption=' FIGURE 1. MA unbound to PI(4,5)P2' scene=''/> | ||
<scene name='User:Nathan_Roy/ | <scene name='User:Nathan_Roy/Residues/1'>TextToBeDisplayed</scene> | ||
| Line 9: | Line 9: | ||
When MA is not bound to PI(4,5)P2 (Figure 1), notice the alignment of helix 1, and more precisely, the orientation of Leu 8 and Glu 12 '' | When MA is not bound to PI(4,5)P2 (Figure 1), notice the alignment of helix 1, and more precisely, the orientation of Leu 8 and Glu 12 <scene name='User:Nathan_Roy/Residues/1'>TextToBeDisplayed</scene>. In this PI(4,5)P2 unbound structure, the myristyl group is sequestered in the pocket of helix 1 created by Leu 8 and Glu 12. Upon binding of PI(4,5)P2 to the hydrophobic groove created by helix 2, a type 2 beta turn, and helix 5, a slight conformational switch occurs in helix 1 (Figure 2), <applet load='2H3Z_mono1.pdb' size='300' frame='true' align='left' caption='FIGURE 2. MA bound to PI(4,5)P2' /> causing a change in the alignment of Leu 8 and Glu 12, ejecting the myristyl group from it's sequestered state. '''INSERT SCENE SHOWING RESIDUES''' This structural switch allows membrane anchoring to be directly coupled to proper membrane localization of Gag, and thus efficient particle release. | ||
Once Gag is localized to discreet sites on the plasma membrane, multimerization of Gag takes place quite quickly , driven by the CA domain, and more specifically our focus here, the C-terminal domain of CA (CTD). There are four helices that contribute to the interaction of CA CTD with it's partner. A side-by-side interaction has been proposed (Figure 3), but many believe the forces involved in the side-by-side model are not great enough to account for the organization and structural stability of assembled Gag. Also, helix 1 of the CA CTD contains a very conserved region of residues within many retroviruses called the MHR (major homology region). In the side-by-side model, the MHR is not responsible for the dimer organization, therefore a model of the CA CTD dimer in which the MHR is responsible for organization of the CA CTD dimers has been sought. <applet load='1aum' size='250' frame='true' align='right' caption='FIGURE 3. Side-by-side structure of CA CTD' /> By making a single deletion of the Ala 177 residue (which lies in the loop between helix 1 and helix 2), the CA CTD domain adopts a domain-swapped conformation, in which the MHR of helix 1 is extended to contact helices 2,3, and 4 of the adjacent CA CTD domain (Figure 4). This domain swapping allows for a tighter binging of the CA CTD domains, and a stronger, and more rigid viral capsid. <applet load='2ont' size='250' frame='true' align='right' caption='FIGURE 4. Domain swapped CA CTD' /> | Once Gag is localized to discreet sites on the plasma membrane, multimerization of Gag takes place quite quickly , driven by the CA domain, and more specifically our focus here, the C-terminal domain of CA (CTD). There are four helices that contribute to the interaction of CA CTD with it's partner. A side-by-side interaction has been proposed (Figure 3), but many believe the forces involved in the side-by-side model are not great enough to account for the organization and structural stability of assembled Gag. Also, helix 1 of the CA CTD contains a very conserved region of residues within many retroviruses called the MHR (major homology region). In the side-by-side model, the MHR is not responsible for the dimer organization, therefore a model of the CA CTD dimer in which the MHR is responsible for organization of the CA CTD dimers has been sought. <applet load='1aum' size='250' frame='true' align='right' caption='FIGURE 3. Side-by-side structure of CA CTD' /> By making a single deletion of the Ala 177 residue (which lies in the loop between helix 1 and helix 2), the CA CTD domain adopts a domain-swapped conformation, in which the MHR of helix 1 is extended to contact helices 2,3, and 4 of the adjacent CA CTD domain (Figure 4). This domain swapping allows for a tighter binging of the CA CTD domains, and a stronger, and more rigid viral capsid. <applet load='2ont' size='250' frame='true' align='right' caption='FIGURE 4. Domain swapped CA CTD' /> | ||