globular proteins proteins with a compact folded structure (with an interior and exterior),...
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Globular Proteins
Proteins with a compact folded structure (with an interior and exterior), generally containing different types of secondary structure elements as well as irregular
regions.
Note: the vast majority of proteins are globular.
Ribbon Diagram Showing Secondary Structures in a Globular Protein
Some Globular Protein Structures
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Myoglobin
Hemoglobin(complex of 4 polypeptide chains or subunits)
Triose phosphate isomerase (complex of 2 subunits) 20S Proteasome (complex of 28 subunits)
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Additional Elements of Structure: Turns
turns turn
R2 often Pro
R2 often Pro
Most common type of turn
R3 never Pro
R3 never Pro
trans-Pro (above) or cis-Pro (in Type VI turns) often found in turns, but rarely in helices and sheets.
Turns with cis-Proline: Type VI
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Type VIa
Type VIb
cis-trans Isomerization of Proline Residues
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Peptidyl-prolyl cis-trans isomerases accelerate the isomerization.
Additional Elements of Structure: Loops
•Irregularly structured elements•More disordered and flexible than turns•Connects secondary structure elements•Variable in length and shape•Frequently form binding sites and enzyme active sites
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The N- and C-terminal arms of proteins are also generally more disordered and irregularly structured.
Domain and Motifs in Globular Proteins: Supersecondary Structure
Some Common Motifs Found in Proteins
motif
hairpin
motif
barrelsbarrel