Sandbox Reserved 1123: Difference between revisions
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=== Structural basis of HIV-1 mature capsid === | === Structural basis of HIV-1 mature capsid === | ||
Each HIV-1 virus owns a '''conical core capsid''' that encapsulates the ssRNA(+) viral genome and some viral enzymes that are essential for the host infection. This capsid contains '''about 250 hexamers and 12 pentamers of the CA protein''', pentamers are important to generate the curvature of the structure. This capsid is the mature capsid, its formation results in the maturation and disassembly of the immature gag polyproteins (first structural protein products which are encoded by the HIV-1 genome) by viral proteases. CA proteins are organized in '''two domains''': an N-terminal domain ( <scene name='71/719864/Ntd_capsid/1'>NTD </scene>) and a C-terminal domain (<scene name='71/719864/Ctd/2'>CTD </scene>). The mature capsid is formed by the assembly of approximately two-thirds of the mature CA proteins in the viral particle. CA proteins bind together and organize themselves in order to create a '''lattice of hexameric rings''', these rings contain an '''inner ring of six <scene name='71/719864/Ntd_capsid/1'>NTD </scene>s''', surrounded by a '''belt of six <scene name='71/719864/Ctd/2'>CTD </scene>s'''. Then, 12 CA pentamers join the structure, it permits the formation of a closed protein shell. <ref name="C"> | Each HIV-1 virus owns a '''conical core capsid''' that encapsulates the ssRNA(+) viral genome and some viral enzymes that are essential for the host infection. This capsid contains '''about 250 hexamers and 12 pentamers of the CA protein''', pentamers are important to generate the curvature of the structure. This capsid is the mature capsid, its formation results in the maturation and disassembly of the immature gag polyproteins (first structural protein products which are encoded by the HIV-1 genome) by viral proteases. CA proteins are organized in '''two domains''': an N-terminal domain ( <scene name='71/719864/Ntd_capsid/1'>NTD </scene>) and a C-terminal domain (<scene name='71/719864/Ctd/2'>CTD </scene>). The mature capsid is formed by the assembly of approximately two-thirds of the mature CA proteins in the viral particle. CA proteins bind together and organize themselves in order to create a '''lattice of hexameric rings''', these rings contain an '''inner ring of six <scene name='71/719864/Ntd_capsid/1'>NTD </scene>s''', surrounded by a '''belt of six <scene name='71/719864/Ctd/2'>CTD </scene>s'''. Then, 12 CA pentamers join the structure, it permits the formation of a closed protein shell. <ref name="C"/> | ||
[[Image:capsid.jpg]] | [[Image:capsid.jpg]] | ||
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=== Primary structure === | === Primary structure === | ||
CA proteins are composed of '''about 230 residues''' [4] and as we mentioned above they contain two domains: <scene name='71/719864/Ntd_capsid/1'>NTD </scene> (in green) and <scene name='71/719864/Ctd/2'>CTD </scene> (in yellow). These two domains are linked together thanks to a <scene name='71/719864/Flexible_linker/2'>Flexible linker </scene> (in orange). <ref name="C"> | CA proteins are composed of '''about 230 residues''' [4] and as we mentioned above they contain two domains: <scene name='71/719864/Ntd_capsid/1'>NTD </scene> (in green) and <scene name='71/719864/Ctd/2'>CTD </scene> (in yellow). These two domains are linked together thanks to a <scene name='71/719864/Flexible_linker/2'>Flexible linker </scene> (in orange). <ref name="C"/> | ||
=== Tertiary structure === | === Tertiary structure === | ||
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Intermolecular NTD-NTD contacts facilitate the formation of the NTD rings, while NTD-CTD contacts maintain the CTD subunits in the belts. There is no intramolecular interaction between the NTD and CTD of each subunit, except the peptidic linkage between these two domains of course. Furthermore, the flexible linker is able to adopt different conformations, which is very useful because the monomers can position themselves in an optimal manner to permit the interaction surfaces in pentamer and hexamer. NTD rings form a rigid structure, this is not the case of CTDs in belts which are mobile and able to rotate, relative to the NTD ring. CTD pivotes such as a rigid body about four intermolecular helix-capping hydrogen bounds at the NTD-CTD interface. | Intermolecular NTD-NTD contacts facilitate the formation of the NTD rings, while NTD-CTD contacts maintain the CTD subunits in the belts. There is no intramolecular interaction between the NTD and CTD of each subunit, except the peptidic linkage between these two domains of course. Furthermore, the flexible linker is able to adopt different conformations, which is very useful because the monomers can position themselves in an optimal manner to permit the interaction surfaces in pentamer and hexamer. NTD rings form a rigid structure, this is not the case of CTDs in belts which are mobile and able to rotate, relative to the NTD ring. CTD pivotes such as a rigid body about four intermolecular helix-capping hydrogen bounds at the NTD-CTD interface. | ||
Thus, each hexameric ring can have slightly different dihedral angles relative to its adjacent rings thanks to the CTDs movments. NTD rings interactions are possible thanks to the first three α-helices of each subunit, they forme a 15-helix barrel in the pentamer and a 18-helix barrel in the hexamer. A small hydrophobic core is located at the center of the bundle thanks to the presence of aliphatic residues, while polar sidechains are present at the periphery and do hydrophilic interactions. | Thus, each hexameric ring can have slightly different dihedral angles relative to its adjacent rings thanks to the CTDs movments. NTD rings interactions are possible thanks to the first three α-helices of each subunit, they forme a 15-helix barrel in the pentamer and a 18-helix barrel in the hexamer. A small hydrophobic core is located at the center of the bundle thanks to the presence of aliphatic residues, while polar sidechains are present at the periphery and do hydrophilic interactions. | ||
[2] <ref name="B"> | [2] <ref name="B"/> | ||
