Globular Proteins Flashcards
Tertiary Protein Structure
- The globular three-dimensional structure (conformation) of a polypeptide that results from the folding, aggregation or interactions of the various regions of secondary structure in a polypeptide as it assumes its biologically active shape
Four Main Chemical Interactions that Help Stabilize Tertiary Structure
- Hydrophobic interactions
- Electrostatic (ionic) interactions.
- Hydrogen bonds.
- Covalent bonds (think disulfides).
Three ways to represent the 3D structure of the small, single chain protein ubiquitin
- Cartoon
- Stick model and close up
- Solvent accessible surface model
Larger proteins often contain two or more distinct _______ of compact folded structure
- “domains”
What is protein tertiary structure characterized by?
- the content of helix and sheet secondary structures as well as defined turns that link these secondary structures
Irregularly structured regions
- random coil
- not all parts of globular protein structure can be categorized as helix, sheet or turn
Unstructured proteins
- some proteins are partially or completely unstructured
- unstructured proteins are referred to as intrinsically unstructured proteins (IUPs) or natively unfolded proteins
- often these proteins are involved in searching out binding partners
First common principle with a dominant motif
- alpha helices like myoglobin
- beta sheets like neuraminidase
- equal amounts of both like TIM
Second common motif
- many proteins are made up of more than one domain
- domain is a compact locally folded region of tertiary structure about 150-250 AA
- Different domains perform different functions
third common principle
- domains may themselves be composed of repeating secondary structure motifs.
Common features of folded globular proteins
- have a nonpolar (hydrophobic) interior and a more hydrophilic exterior
- B sheets are usually twisted or wrapped into barrel structures
- the polypeptide chain can turn corners
How does protein folding occur
- a non random process
- occurs in a stepwise manner with free energy decreasing at each step
- steps are not always the same or in the same order
When does formation of secondary structure occur?
- alpha helices and B sheets formation is an early process
Folding of larger polypeptides involves _____ intermediates
- “stable”
- molten globules
What is the purpose of hydrophobic interactions
- exclude water molecules while directing and sequestering hydrophobic residues towards the interior of the folding protein
What does solvent exclusion, van der waals forces and H bonding help to do?
- align secondary structures
The molten globule
- a compact, partially folded intermediate state that has native-like secondary structure and backbone folding topology, but lacks defined tertiary structure interactions of the native state
Energy Landscape Model
- aka folding funnel explains how conformational restriction can be achieved during folding.