PMID- 9079381
OWN - NLM
STAT- MEDLINE
DCOM- 19970425
LR  - 20061115
IS  - 1359-0278 (Print)
IS  - 1359-0278 (Linking)
VI  - 1
IP  - 3
DP  - 1996
TI  - Towards the complete structural characterization of a protein folding pathway:
      the structures of the denatured, transition and native states for the
      association/folding of two complementary fragments of cleaved chymotrypsin
      inhibitor 2. Direct evidence for a nucleation-condensation mechanism.
PG  - 189-208
AB  - BACKGROUND: Single-module proteins, such as chymotrypsin inhibitor 2 (CI2), fold 
      as a single cooperative unit. To solve its folding pathway, we must characterize,
      under conditions that favour folding, its denatured state, its transition state, 
      and its final folded structure. To obtain a "denatured state' that can readily be
      thus characterized, we have used a trick of cleaving CI2 into two complementary
      fragments that associate and fold in a similar way to intact protein. RESULTS:
      Fragment CI2(1-40)-which contains the sequence of the single alpha-helix,
      spanning residues 12-24-and CI2(41-64), and mutants thereof, were analyzed by NMR
      spectroscopy, the transition state for association/folding was characterized by
      the protein engineering method, and the structure of the complex was solved by
      NMR and X-ray crystallography. Both isolated fragments are largely disordered.
      The transition state for association/folding is structured around a nucleus of a 
      nearly fully formed alpha-helix, as is the transition state for the folding of
      intact CI2, from residues Ser12 to Leu21, Ala16, a residue from the helix whose
      sidechain is buried in the hydrophobic core, makes interactions with Leu49 and
      Ile57 in the other fragment. Ala16 makes its full interaction energy in the
      transition state for the association/folding reaction, just as found during the
      folding of the intact protein. CONCLUSIONS: The specific contacts in the
      transition state from a nucleus that extends from one fragment to the next, but
      the nucleus is only "flickeringly' present in the denatured state. This is direct
      evidence for the nucleation-condensation mechanism in which the nucleus is only
      weakly formed in the ground state and develops in the transition state. The low
      conformational preferences in the denatured state are not enough to induce
      significant local secondary structure, but are reinforced by tertiary
      interactions during the rapid condensation around the nucleus.
FAU - Neira, J L
AU  - Neira JL
AD  - MRC Unit for Protein Function and Design, Cambridge Centre for Protein
      Engineering, UK.
FAU - Davis, B
AU  - Davis B
FAU - Ladurner, A G
AU  - Ladurner AG
FAU - Buckle, A M
AU  - Buckle AM
FAU - Gay, G de P
AU  - Gay Gde P
FAU - Fersht, A R
AU  - Fersht AR
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PL  - England
TA  - Fold Des
JT  - Folding & design
JID - 9604387
RN  - 0 (Peptide Fragments)
RN  - 0 (Peptides)
RN  - 0 (Plant Proteins)
RN  - 0 (Solutions)
RN  - 0 (chymotrypsin inhibitor 2)
RN  - EC 3.4.21.1 (Chymotrypsin)
SB  - IM
MH  - Amino Acid Sequence
MH  - Chymotrypsin/*antagonists & inhibitors
MH  - Crystallization
MH  - Crystallography, X-Ray
MH  - Magnetic Resonance Spectroscopy
MH  - Models, Molecular
MH  - Molecular Sequence Data
MH  - Molecular Structure
MH  - Peptide Fragments/chemistry/genetics
MH  - Peptides/*chemistry/genetics
MH  - Plant Proteins
MH  - Protein Conformation
MH  - Protein Denaturation
MH  - Protein Engineering
MH  - Protein Folding
MH  - Protein Structure, Secondary
MH  - Solutions
EDAT- 1996/01/01 00:00
MHDA- 1996/01/01 00:01
CRDT- 1996/01/01 00:00
PHST- 1996/01/01 00:00 [pubmed]
PHST- 1996/01/01 00:01 [medline]
PHST- 1996/01/01 00:00 [entrez]
PST - ppublish
SO  - Fold Des. 1996;1(3):189-208.