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 Myoglobin Hemoglobin (complex of 4 polypeptide chains or subunits) Triose phosphate isomerase (complex of 2 subunits)20S Proteasome (complex of 28 subunits)

Additional Elements of Structure: Turns  turns  turn R2 often Pro Most common type of turn 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 Type VIa Type VIb

cis-trans Isomerization of Proline Residues 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 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  barrels  barrel