PDBsum entry 2k91

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protein Protein-protein interface(s) links
Hormone PDB id
Protein chains
21 a.a.
30 a.a. *
* Residue conservation analysis
PDB id:
Name: Hormone
Title: Enhancing the activity of insulin by stereospecific unfolding
Structure: Insulin. Chain: a. Fragment: unp residues 90-110. Synonym: insulin b chain, insulin a chain. Engineered: yes. Insulin. Chain: b. Fragment: unp residues 25-54. Synonym: insulin b chain, insulin a chain.
Source: Homo sapiens. Organism_taxid: 9606. Expressed in: escherichia coli. Expression_system_taxid: 562.
NMR struc: 20 models
Authors: Q.X.Hua,B.Xu,K.Huang,S.Q.Hu,S.Nakarawa,W.H.Jia, N.F.P.Philips,L.Wittaker,J.Wittaker,P.G.Katsoyannis, M.A.Weiss
Key ref:
Q.X.Hua et al. (2009). Enhancing the Activity of a Protein by Stereospecific Unfolding: CONFORMATIONAL LIFE CYCLE OF INSULIN AND ITS EVOLUTIONARY ORIGINS. J Biol Chem, 284, 14586-14596. PubMed id: 19321436 DOI: 10.1074/jbc.M900085200
29-Sep-08     Release date:   18-Nov-08    
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Protein chain
Pfam   ArchSchema ?
P01308  (INS_HUMAN) -  Insulin
110 a.a.
21 a.a.
Protein chain
Pfam   ArchSchema ?
P01308  (INS_HUMAN) -  Insulin
110 a.a.
30 a.a.*
Key:    PfamA domain  Secondary structure
* PDB and UniProt seqs differ at 4 residue positions (black crosses)

 Gene Ontology (GO) functional annotation 
  GO annot!
  Cellular component     extracellular region   1 term 
  Biochemical function     hormone activity     1 term  


DOI no: 10.1074/jbc.M900085200 J Biol Chem 284:14586-14596 (2009)
PubMed id: 19321436  
Enhancing the Activity of a Protein by Stereospecific Unfolding: CONFORMATIONAL LIFE CYCLE OF INSULIN AND ITS EVOLUTIONARY ORIGINS.
Q.X.Hua, B.Xu, K.Huang, S.Q.Hu, S.Nakagawa, W.Jia, S.Wang, J.Whittaker, P.G.Katsoyannis, M.A.Weiss.
A central tenet of molecular biology holds that the function of a protein is mediated by its structure. An inactive ground-state conformation may nonetheless be enjoined by the interplay of competing biological constraints. A model is provided by insulin, well characterized at atomic resolution by x-ray crystallography. Here, we demonstrate that the activity of the hormone is enhanced by stereospecific unfolding of a conserved structural element. A bifunctional beta-strand mediates both self-assembly (within beta-cell storage vesicles) and receptor binding (in the bloodstream). This strand is anchored by an invariant side chain (Phe(B24)); its substitution by Ala leads to an unstable but native-like analog of low activity. Substitution by d-Ala is equally destabilizing, and yet the protein diastereomer exhibits enhanced activity with segmental unfolding of the beta-strand. Corresponding photoactivable derivatives (containing l- or d-para-azido-Phe) cross-link to the insulin receptor with higher d-specific efficiency. Aberrant exposure of hydrophobic surfaces in the analogs is associated with accelerated fibrillation, a form of aggregation-coupled misfolding associated with cellular toxicity. Conservation of Phe(B24), enforced by its dual role in native self-assembly and induced fit, thus highlights the implicit role of misfolding as an evolutionary constraint. Whereas classical crystal structures of insulin depict its storage form, signaling requires engagement of a detachable arm at an extended receptor interface. Because this active conformation resembles an amyloidogenic intermediate, we envisage that induced fit and self-assembly represent complementary molecular adaptations to potential proteotoxicity. The cryptic threat of misfolding poses a universal constraint in the evolution of polypeptide sequences.
  Selected figure(s)  
Figure 2.
Role of Phe^B24 in an insulin monomer. A, shown is a cylinder model of insulin as a T-state protomer. The C-terminal B-chain β-strand is shown in blue, and the Phe^B24 side chain is shown in tawny. The black portion of the N-terminal A-chain α-helix (labeled buried) indicates a hidden receptor-binding surface (Ile^A2 and Val^A3). B, the schematic representation of insulin highlights the proposed role of the Phe^B24 side chain as a plug that inserts into a crevice at the edge of the hydrophobic core. C and D, whereas substitution of Phe^B24 by l-Ala (C) would only partially fill the B24-related crevice, its substitution by d-Ala (D) would be associated with a marked packing defect. An alternative conformation, designated the R-state, is observed in zinc insulin hexamers at high ionic strength (74) and upon binding of small cyclic alcohols (75) but has not been observed in an insulin monomer.
Figure 8.
Insulin fibrillation. A, proposed pathway of insulin fibrillation via partial unfolding of the monomer (33, 76, 77). The native state is protected by classical self-assembly (far left). Disassembly leads to equilibrium between native and partially folded monomers (open triangle and magenta trapezoid, respectively). This partial fold may unfold completely as an off-pathway event or aggregate to form a nucleus en route to a protofilament (far right). B, detachment of the C-terminal B-chain β-strand (dashed purple line) may lead to a putative amyloidogenic intermediate (middle) (35) and formation of fibrils (electron microscopic photomicrograph; right). In the model of the partial fold, cylinders indicate helical substructure (residues B9-B19 (blue) and residues A16-A20 (red)). Dashed lines indicate disordered regions; disulfide bridges are indicated by black balls (sulfur atoms). Scale bar = 200 nm. A was adapted from the results of Fink and co-workers (33).
  The above figures are reprinted by permission from the ASBMB: J Biol Chem (2009, 284, 14586-14596) copyright 2009.  
  Figures were selected by an automated process.  

Literature references that cite this PDB file's key reference

  PubMed id Reference
20948967 M.Liu, L.Haataja, J.Wright, N.P.Wickramasinghe, Q.X.Hua, N.F.Phillips, F.Barbetti, M.A.Weiss, and P.Arvan (2010).
Mutant INS-gene induced diabetes of youth: proinsulin cysteine residues impose dominant-negative inhibition on wild-type proinsulin transport.
  PLoS One, 5, e13333.  
20106984 Y.Yang, A.Petkova, K.Huang, B.Xu, Q.X.Hua, I.J.Ye, Y.C.Chu, S.Q.Hu, N.B.Phillips, J.Whittaker, F.Ismail-Beigi, R.B.Mackin, P.G.Katsoyannis, R.Tycko, and M.A.Weiss (2010).
An Achilles' heel in an amyloidogenic protein and its repair: insulin fibrillation and therapeutic design.
  J Biol Chem, 285, 10806-10821.  
19321435 B.Xu, K.Huang, Y.C.Chu, S.Q.Hu, S.Nakagawa, S.Wang, R.Y.Wang, J.Whittaker, P.G.Katsoyannis, and M.A.Weiss (2009).
Decoding the cryptic active conformation of a protein by synthetic photoscanning: insulin inserts a detachable arm between receptor domains.
  J Biol Chem, 284, 14597-14608.  
19395706 M.A.Weiss (2009).
Proinsulin and the genetics of diabetes mellitus.
  J Biol Chem, 284, 19159-19163.  
19850922 M.Liu, Z.L.Wan, Y.C.Chu, H.Aladdin, B.Klaproth, M.Choquette, Q.X.Hua, R.B.Mackin, J.S.Rao, P.De Meyts, P.G.Katsoyannis, P.Arvan, and M.A.Weiss (2009).
Crystal structure of a "nonfoldable" insulin: impaired folding efficiency despite native activity.
  J Biol Chem, 284, 35259-35272.
PDB code: 3gky
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