|Lecture Notes: 12 February||
Secondary Structure/Motifs, cont.
Aside: Fibrous proteins, cont:
- anti-parallel -pleated sheet (silk)
- Collagen strand: This is a specialized structure occurring in only a particular family of fibrous proteins. It does not occur in globular proteins that I am aware of.
- Collagen triple helix. Note repeating sequence of -(gly-x-y)- where x is usually proline and y is usually hydroxyproline. (Fig 4.36) [overheads: 11-8&10, S; 4-10 to 12]
Non-repetitive secondary elements: Proteins can also have non-repetitive secondary structures which consist of a few residues in a turn or loop. Among these are:
- Type I turns: Fig. 4.18, left [overhead 7.22, V&V] four amino acid residues in a 180° turn, usually H-bonded between the carbonyl O of the first residue and the amide N of the fourth. Proline is often the second residue. [overhead, 7-22 V&V]
- Type II turns: Fig. 4.18 [overhead 7.22, V&V] four amino acid residues in a 180° turn, usually H-bonded between the carbonyl O of the first residue and the amide N of the fourth. Glycine is most frequently the third residue and proline is often the second residue. [overhead, 7-22 V&V]
A partial turn of a 310 helix. Short sections of this helix often occur at the ends of alpha-helixes as transitional elements.
The Tertiary structure describes the overall folding of a single covalent structure.
As the number of known protein structures increased additional patterns became obvious within the tertiary level of structure: Motifs & Domains.
Quaternary (4°) structures (Fig. 4.25; overheads: MvH 6.26, Fig 25): Geometrically specific associations of protein subunits; the spatial arrangement of protein subunits.
Rationale for quaternary: There are a variety of advantages to large structures:
Quaternary structures allows the assembly of large to extremely large structures.
Let's look at how the various levels of structure go ingto making a typical multimeric protein:
Last modified 14 February 2010