Globular Proteins

Globular proteins have a molecular structure that has the appearance of a glob whose 3D structure is anywhere from a sphere to a cigar. Usually the structure of a globular protein is divided into three or four levels. The primary structure is simply the sequence of amino acids forming the peptide chain. The peptide chain is folded in a repetitive fashion, and these structures with repetitive conformations are called secondary structures. Common examples of secondary structures are α-helix and β-sheets. The tertiary structure is the overall 3D structure of a protein molecule and is produced by folding the secondary structures upon themselves, and in the process the sections of the peptide that were not involved in secondary structures form turns (tight loops) and loops. Some globular proteins have a quaternary structure, and it is formed when two or more globular protein molecules (monomer) join together and form a multimeric unit. One way of characterizing globular proteins is by the number of layers of backbones the tertiary structures contain. A convenient way of classifying globular proteins is to categorize them according to the type and arrangement of secondary structures that are present and the intramolecular forces that are produced by these arrangements. The focus of the content of this page is on the tertiary structures of globular proteins illustrating the characteristics of their different backbone layers, their different classes and the intramolecular forces maintaining the tertiary structures.

Layers of Backbone Present in the StructureLayers of Backbone Present in the Structure

Layers of backbone in the core of the structure is a feature that many, but not all, globular proteins have. The number of layers and their location vary for different proteins, but, in all case that have layers, the hydrophobic forces between the layers play a major role in maintaining the tertiary structure.

	spinqualitylabelsall models PDB ID 1a7v Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image
	Tertiary Structures of Examples

Two LayersTwo Layers

The ribbons representing the backbones show the two layers of α-helices. The are shown in ball and stick with one layer colored green and the other cyan. Notice that these side chains are mostly located between the layers and that few are on the exterior of the molecule. The are now ball & stick, and they tend to be on the surface of the molecule and not between the layers. so that axis of helix aligns with z-axis.

Three LayersThree Layers

Rotate the to observe the three layers. Hopefully you positioned some like .