Protein Structure. beta sheets are twisted. Parallel sheets are less twisted than antiparallel and are always buried. In contrast, antiparallel sheets can withstand greater distortions (twisting and beta-bulges) and greater exposure to solvent.
This chirality gives the twist and distorts H-bonding.
A tug of war exists between conformational energies of the side chain and maximal H-bonding.
Triose phosphate isomerase
Turns - coils or loops link regions of secondary structure
50% of structure of globular proteins are not repeating structures
type I and type II :hairpin turn between anti parallel sheets
Type I f2 = -60o, y2 = -30o
f3 = -90o, y3 = 0o
Type II f2 = -60o, y2 = 120o
f3 = 90o, y3 = 0o
Certain amino sequences have patterns to their folding.
A. bab motif, B. b hairpin C. aa motif
There is an estimate of about 10000 different folding patterns in proteins
About half of the proteins fall into a few dozen folding patterns.
Those proteins related by structure are called families.
A large Family are the c cytochromes (see Figure 6-31 pg 147 in FOB.)
The plane.b barrel has several types of structures that have been mimicked in art.
B. Human prealbumin or porins
C. Triose phosphate isomerase
Mostly a b barrel motif
H2CO3- CO2 + H2O
Binding NADH in the Rossmann fold.
C2H2 zinc finger: It is characterized by the sequence CX2-4C....HX2-4H, where C = cysteine, H = histidine, X = any amino acid.
C4 zinc finger: Its consensus sequence is CX2CX13CX2CX14-15CX5CX9CX2C. The first four cysteine residues bind to a zinc ion and the last four cysteine residues bind to another zinc ion
C6 zinc finger. It has the consensus sequence CX2CX6CX5-6CX2CX6C. The yeast's Gal4 contains such a motif where six cysteine residues interact with two zinc ions