Protein Structure 2Higher Order Protein Structures

Hierarchy of Protein Structure

Primary sequence- The amino acid sequence of a polypeptide, listed from N-terminus to C-terminus.Secondary structure- Recurring structural feature of proteins stabilized exclusively by hydrogen bonds between peptide bond elements. Supersecondary structure- Recurring structural feature of proteins composed of two or more secondary structural elements. Domain- A segment of protein structure that is autonomously stable. Tertiary structure- A stable, independent protein encoded by a single gene.

Quaternary structure- A complex structure composed of two or more tertiary structure subunits.

Alpha-fibrous proteins: Coiled-coil Helix Supersecondary Structure

Heptad repeats in GCN4

Four-helical bundle

Sequence Comparison Reveals Positional Preference Within Heptad Repeats

Max1 as an Example of a Leucine Zipper Motif Protein

Parallel and Anti-parallel Beta Sheets

anti-parallel parallel

Supersecondary Structures

Structure of -grasp fold of ubiquitin showing motif

Repeating motifs (n=7) form a Rossmann fold structure

Supersecondary Structures

Greek key motif

Beta meander motif

-coil- Supersecondary Structure

IpaH3.0

Domains and Tertiary Structure

Domains- Structurally autologous structures possessing discrete functions that comprises part of the tertiary structure (beads on a string). Domains can be identified by their characteristic sequences.

Ex: DNA binding domains, NAD+/NADP+ binding domains, HECT domains, Zn finger domains, etc.

Motif- A highly conserved, short amino acid sequence that identifies a discrete function.

Ex: Protein kinase phosphorylation motifs, Ca++ binding motifs, etc.

Pyruvate kinase domain structure

Quaternary Structure