globular proteins proteins with a compact folded structure (with an interior and exterior),...

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