Globular Proteins: Difference between revisions
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==== Mixed α-helix and β-Sheet ==== | ==== Mixed α-helix and β-Sheet ==== | ||
* <scene name='Globular_Proteins/Tmvp2/1'>Tobacco mosaic virus protein</scene> - forms the capsid of the virus. Again the α-helices, loops and turns are prominent features, and the α-helices are antiparallel. | * <scene name='Globular_Proteins/Tmvp2/1'>Tobacco mosaic virus protein</scene> - forms the capsid of the virus. Again the α-helices, loops and turns are prominent features, and the α-helices are antiparallel. | ||
* <scene name='Globular_Proteins/Porin/1'>Matrix porin</scene> - integral protein from the outer membrane of ''E. coli''. Since the barrel structure is inserted into the interior of the membrane, the outer surface that contacts the membrane must be largely <scene name='Globular_Proteins/Porin_phobic/1'>hydrophobic</scene>, but the ends and much of the interior is <scene name='Globular_Proteins/Porin_polar/1'>polar</scene>. <scene name='Globular_Proteins/Porin_polar_phobic/1'>Both</scene> shown together. | * <scene name='Globular_Proteins/Porin/1'>Matrix porin</scene> - integral protein from the outer membrane of ''E. coli''. Since the barrel structure is inserted into the interior of the membrane, the outer surface that contacts the membrane must be largely <scene name='Globular_Proteins/Porin_phobic/1'>hydrophobic</scene>, but the ends, which contact water, and much of the interior is <scene name='Globular_Proteins/Porin_polar/1'>polar</scene>. <scene name='Globular_Proteins/Porin_polar_phobic/1'>Both</scene> shown together. | ||
* <scene name='Globular_Proteins/Concan/1'>Concanavalin</scene> - Example of another lectin. Notice that the tertiary structures of the three lectins are different revealing that the structures can be different but yet have the same general function. There are two antiparallel β-sheets with the hydrophobic sides of the sheets facing each other. They are interlocking β-Sheets or have Greek Key Topology, ''i.e.'' after laying down a strand in a sheet, often the peptide chain loops over to the other sheet and lays down a strand in that sheet. | * <scene name='Globular_Proteins/Concan/1'>Concanavalin</scene> - Example of another lectin. Notice that the tertiary structures of the three lectins are different revealing that the structures can be different but yet have the same general function. There are two antiparallel β-sheets with the hydrophobic sides of the sheets facing each other. They are interlocking β-Sheets or have Greek Key Topology, ''i.e.'' after laying down a strand in a sheet, often the peptide chain loops over to the other sheet and lays down a strand in that sheet. | ||
* <scene name='Globular_Proteins/Crystallin/1'>Gamma-Crystallin</scene> - A protein that is a component of the eye lense. This protein is another example of interlocking β-sheet, two of the Greek key bilayers are connected by a looping peptide segment. | * <scene name='Globular_Proteins/Crystallin/1'>Gamma-Crystallin</scene> - A protein that is a component of the eye lense. This protein is another example of interlocking β-sheet, two of the Greek key bilayers are connected by a looping peptide segment. | ||
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{{Clear}} | {{Clear}} | ||
== Other Characteristics == | == Other Characteristics == | ||
Disulfide bonds and metal ion chelates can stabilize the tertiary structure in the absence of well organized layers which generate hydrophobic attractions. Some proteins are small in size and therefore do not have large amounts of backbone that can be organized into layers. Others have significant backbone, but the layers are not well organized and therefore are non-stabilizing. The attractions formed by metal ions chelates or disulfide bonds in these proteins are as important or more so than the hydrophobic interactions of the organized layers. | Disulfide bonds and metal ion chelates can stabilize the tertiary structure in the absence of well organized layers which generate hydrophobic attractions. Some proteins are small in size and therefore do not have large amounts of backbone that can be organized into layers. Others have significant backbone, but the layers are not well organized and therefore are non-stabilizing. The attractions formed by metal ions chelates or disulfide bonds in these proteins are as important or more so than the hydrophobic interactions of the organized layers. Some proteins are intrinsically unstructured. They do have secondary structure, but these structural components are not extensively folded back on themselves resulting in a more extended conformation. With this extended conformation these proteins do not have binding pockets normally found in globular proteins so as a consequence binding to these proteins occurs over a relatively large surface area. | ||
<StructureSection load='2ben' size='500' side='right' caption='' scene='Globular_Proteins/Insulin1/1'>__NOTOC__ | <StructureSection load='2ben' size='500' side='right' caption='' scene='Globular_Proteins/Insulin1/1'>__NOTOC__ | ||
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=== Intrinsically Unstructured Proteins === | === Intrinsically Unstructured Proteins === | ||
<scene name='Globular_Proteins/Catenin/ | <scene name='Globular_Proteins/Catenin/2'>β-catenin</scene> - one of several catenin. You may notice that residues 550-561 are missing most likely because they form an unordered segment. Show bound to <scene name='Globular_Proteins/Catenin3/1'>lymphoid enhancer-binding factor 1</scene> (LEF-1). LEF-1 is missing residues 26-47, again an unordered segment. Fill in this gap in your mind's eye, and you will see the large area over which the LEF-1 is binding. | ||