Steric Constraints on phi psi Unfavorable orbital overlap precludes some combinations of phi and psi Nonbonded contact R Nonbonded radius =-60,V=180° A furtherφ rolation of120° removes the bulky carbonyl 中=0,v=180 中=180°,v=0 group as far as possible 0=0°,=0° from the side chain phi=0, psi=180 is unfavorable phi=180, psi=0 is unfavorable phi=0, psi=0 is unfavorable
Unfavorable orbital overlap precludes some combinations of phi and psi •phi = 0, psi = 180 is unfavorable •phi = 180, psi = 0 is unfavorable •phi = 0, psi = 0 is unfavorable Steric Constraints on phi & psi
Steric Constraints on phi psi Parallel B-sheet eft-handed Antiparallel B-sheet a-helix triple helix G.N. Ramachandra Right-handed a-helix
• G. N. Ramachandran Steric Constraints on phi & psi
Classes of secondary structure these are le0cal(局部) structures that are stabilized by hydrogen bonds a helix 阝- sheet turns 阝- bulge coil
Classes of Secondary Structure all these are local（局部） structures that are stabilized by hydrogen bonds • α-helix • β-sheet • β-turns • β-bulge • coil
The Alpha helix first proposed by linus Pauling and Robert corey in 1951 A ubiquitous component of proteins Stabilized by h-bonds
The Alpha Helix • First proposed by Linus Pauling and Robert Corey in 1951 • A ubiquitous component of proteins • Stabilized by H-bonds
Side (d) Hydrogen bonds stabilize The helix can be viewed the helix stracture aray peptide planes hinged at the a-carbons and proximately pan to the helix