by Yogesh kumar THE STRUCTURE OF PROTEINSTWO HYDROGEN-BONDEDHELICAL CONFIGURATIONS OF THE POL YPEPTIDE CHAIN (February 28 1951) JACS

1. THE STRUCTURE OF PROTEINS
TWO HYDROGEN-BONDED
HELICAL CONFIGURATIONS OF THE POL YPEPTIDE
CHAIN (February 28 1951) JACS
Linus Carl Pauling, Robert B.Corey & H.R.Brason
The Nobel Prize in Chemistry 1954
Presented by
Yogesh Kumar
CSIR-CIMAP-JNU (Ph.D)

2. Protein Structures

3. All hydrogen bonds should be satisfied,
i.e. distance N-O of about 2.7Å and angle
between C = O and H – N less then ~30
Distances and angles
Between atoms
Determinants of helical structure
C-C=1.53Å ,
C==O = 1.23Å
C-N=1.32Å
N-CR=1.47

4. Models satisfies all constraints
3.6 residues per turn
The number of residues per turn in Pauling's final model was 3.6. Today alpha helix is
also known as (3.6 13 alpha ) helix . One helix contain 3.6 residues and 13 atoms

5. The helix with 5.1 residues per turn
The helix with 5.1 residues per turn.
The pi helix with 5.1 residues per turn--have yet to be found in nature and may not
exist at all.

6. The α-helix – one of the two common
structural elements in proteins
 Completes one turn every 3.6 residues
 Rises ~5.4 Å with each turn
 Has hydrogen bonds between the C=O of residue i
and the N-H of residue i+4
 Is right-handed
i
i+4
C
N
O
Complete one turn consist of 3.6 residues and each
residue take 1.5 Å rise. So ( 1.5*3.6=5.5 Å.)

7. Why did Pauling and Corey succeed where
others failed?
• The researchers who came up with earlier theories were crystallographers.
• They were used to crystals in which everything is made up of integral
numbers," said Eisenberg. "Pauling was a broader, structural chemist--he was
able to think outside the box.
• They did not consider only models with integer number of residues per turn!”
• Understanding the importance of hydrogen bonds
• Taking into account the planar peptide bond
• Better knowledge of covalent bond lengths and angles

8. • Pauling and Corey's work was not
without mistakes: research since the
1951 protein papers found the beta
sheet to be twisted, not flat as
suggested in Corey and Pauling's
research.
• Since Pauling and Corey's famous
series was first published, the ideas
their explanation have proceeded
from hypothesis to accepted fact to
common knowledge.
• Dramatic verification of their work
came in 1958, when the three-
dimensional structure of myoglobin
was found to be composed almost
solely of alpha helices
Mistakes
Proof came 7 years later…
John Cowdery Kendrew
The Nobel Prize in Chemistry 1962
Kendrew, J. C., Bodo, G., Dintzis, H. M. Parrish, R. G., Wyckoff, H.,
and Phillips, D. C. A Three-Dimensional Model of the Myoglobin
Molecule
Obtained by X-ray Analysis. Nature, 181, 662 (1958).

9. Hierarchy of Protein Structure
Linear chain made of 20 possible
amino acids
Alpha-helices, beta-sheets, turns
Motifs, domains
Oligomers, complexes

10. The Protein Data Bank (www.pdb.org)
Linus Pauling, Robert B.corey, and H. R. Branson* The structure of Proteins: Two Hydrogen-Bonded Helical Confirmations Of the
polypeptide chain,.JACS, Vol37, 1951

11. Thank You