Coiled coil: Difference between revisions
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A coiled-coil or superhelix is formed by coiling two, three or four α-helices together. The helical strands are held together by the hydrophobic force formed between nonpolar side chains from the | A '''coiled-coil''' or '''superhelix''' is formed by coiling two, three or four α-helices together. The helical strands are held together by the hydrophobic force formed between nonpolar side chains from the | ||
different peptide strands. A <b>heptad repeat</b> pattern of short chain hydrophobic residues in the primary structure consistently bring these nonpolar side chains | different peptide strands. A <b>heptad repeat</b> pattern of short chain hydrophobic residues in the primary structure consistently bring these nonpolar side chains | ||
together every seventh residue. These nonpolar residues from different strands are properly located to interact with one another because the helix is slightly distorted by being less tightly wound than the normal α-helix so that it has a pitch of 0.51 instead of 0.54 and there | together every seventh residue. These nonpolar residues from different strands are properly located to interact with one another because the helix is slightly distorted by being less tightly wound than the normal α-helix so that it has a pitch of 0.51 instead of 0.54 and there | ||
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<kinemage align="right" width="400" height="300" file="coiled_coil1.kin" /> | <kinemage align="right" width="400" height="300" file="coiled_coil1.kin" /> | ||
Fibrous proteins are, for the most part, characterized by highly repetitive simple sequences such as a coiled coil of two alpha helices such as | Fibrous proteins are, for the most part, characterized by highly repetitive simple sequences such as a coiled coil of two alpha helices such as in [[keratins]] and tropomyosin. Shown here is a ribbon diagram of a coiled coil. One of the segment's two identical chains, "Coil 1", is yellow and the other, "Coil 2", is seagreen. The N- and C-terminal ends of each segment are marked by blue and red balls. You can readily see that the protein forms a parallel coiled coil: its component alpha helices are right-handed but the coiled coil is left-handed. Look at Views1-3 to see the coiled coil from different angles. Drag the 'zclip' slide left and right in View3 to see part or all of the structure. Note that the coiled coil makes only slightly more than 1/2 turn over a distance in which each alpha helix makes ~13 turns. | ||
Drag the mouse from side to side horizontally across the image to see the way in which the two coils wrap around each other. Parallel coiled coils occur in many proteins including alpha keratin, a fibrous stress-bearing protein occurring in mammalian skin; tropomyosin and myosin, important proteins in muscle; and the so-called leucine zipper segments that permit the dimerization and hence activation of numerous eukaryotic transcription factors. Leucine zippers differ from other 2-helix coiled coils only in that their d-residues are almost invariably Leu. | Drag the mouse from side to side horizontally across the image to see the way in which the two coils wrap around each other. Parallel coiled coils occur in many proteins including alpha keratin, a fibrous stress-bearing protein occurring in mammalian skin; tropomyosin and myosin, important proteins in muscle; and the so-called leucine zipper segments that permit the dimerization and hence activation of numerous eukaryotic transcription factors. Leucine zippers differ from other 2-helix coiled coils only in that their d-residues are almost invariably Leu. | ||
==The Heptad Repeat and Hydrophobic Interactions in Coiled Coils.== | ==The Heptad Repeat and Hydrophobic Interactions in Coiled Coils.== | ||
<kinemage align="right" width="400" height="480" file="coiled_coil2_3.kin" /> | <kinemage align="right" width="400" height="480" file="coiled_coil2_3.kin" /> | ||
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== Additional Illustrations == | == Additional Illustrations == | ||
<Structure load='1UO2' size='500' frame='true' align='right' caption=' | <Structure load='1UO2' size='500' frame='true' align='right' caption='Coiled-cil from GCN4 (PDB code [[1uo2]])' scene='Coiled_coil/Gcn4/1' /> | ||
Two strands of general control protein GCN4 from baker's yeast. Observe the slight coil in the strands. (<scene name='Coiled_coil/Gcn4/1'>Initial scene</scene>) Every seventh residue, <scene name='Coiled_coil/Gcn4_2/1'>shown in spacefill</scene>, is nonpolar, and with 3.5 residues per turn each heptad repeat is aligned with the one below and above it, as well as being in position to interact with the heptad repeat on a second strand. Looking down the <scene name='Coiled_coil/Gcn4_3/1'>spline</scene> of the contact. The <scene name='Coiled_coil/Gcn4_4/1'>side chains</scene> of the residues located between the heptad repeats spiral around the helix away from the side chains on the partner strand, thus not permitting interactions between these side chains of the two strands. | |||
Three coiled strands of <scene name='Coiled_coil/Hemagglu/1'>influenza hemagglutinin</scene> (1HTM) which is one of the viral proteins that is immunologically active. The heptrad repeats of each strand are shown in <scene name='Coiled_coil/Hemagglu_2/1'>spacefill</scene>. | |||
Four strands of the general control protein showing the <scene name='Coiled_coil/Gcn4_5/1'>heptad repeats</scene> on all four chains. | |||
<scene name='Coiled_coil/Cap/1'>Catabolite Activator Protein</scene> (CAP; 1G6N.PDB) is a globular protein that is an important regulator of several aspects of catabolism. Notice the two coiled α-helices in the center of the structure. Each coil is a part of a different subunit, and the formation of the coiled-coil plays a pivotal role in holding the two subunits together. The <scene name='Coiled_coil/Cap_2/1'>heptrad repeats</scene> in each subunit are shown in spacefill. | |||
{{Clear}} | |||
==Coordinates== | ==Coordinates== | ||
The coordinates for the coiled-coil (tropomyosin) were obtained from Xiaoling Xia and Carolyn Cohen, Brandeis University. | The coordinates for the coiled-coil (tropomyosin) were obtained from Xiaoling Xia and Carolyn Cohen, Brandeis University. | ||