LEVELS OF PROTEIN STRUCTURE AND MISFOLDING

what factors determine protein shape and function (8)

• R groups/ side chains

can vary chemically: polar, non-polar, acidic, basic

• amino acid sequence

• chaperones: barrel shaped proteins that assist in protein folding, requires energy from ATP, often for hydrophobic proteins which excludes water from environment

• water

• H bonds

• cysteine bonds

• flexibility

• regular structures i.e. helices/ sheets

what are the levels of protein structure

• primary

• secondary

• tertiary

• quaternary

primary structure of proteins

• linear sequence of amino acids

• the most basic level

secondary structure of proteins

• local regions formed into regular structures

2 most common: alpha helix, beta pleated sheets

• alpha helix: tightly coiled rod, globular, found in membrane spanning proteins e.g. heptahelical

important for binding DNA

• beta pleated sheets: H bonds between 2 parts of protein that can be far apart

• structural motifs: grouping of a few short segments of secondary structural elements e.g. helix-turn-helix

• non regular coils, hinges and loops

tertiary structure of proteins

• folding of single polypeptide chain/ protein into 3D conformation

can provide binding sites for ligands

• motifs coming together

• domains within tertiary structures are a functionally specialised region that allows protein to be multifunctional within itself

folds independently and has a distinct structure and function

quaternary structure of proteins

• multiple chains/ subunit complex of individual polypeptide chains

increases protein stability

• suubunits can be the same (homo-polypeptide) or different (hetero-polypeptide)

• e.g. haemoglobin

how protein misfolding can cause disease

• groups of misfolded proteins: aggregations

tightly packed stable beta sheets

linked to Alzheimer’s, Huntington’s, Parkinson’s

• treatment: pharmaceutical chaperones

• e.g. misfolded prion proteins can cause other prion proteins to misfold