PDBsum entry 1r9o

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Oxidoreductase PDB id
Protein chain
455 a.a. *
Waters ×255
* Residue conservation analysis
PDB id:
Name: Oxidoreductase
Title: Crystal structure of p4502c9 with flurbiprofen bound
Structure: Cytochrome p450 2c9. Chain: a. Fragment: catalytic domain. Synonym: cypiic9, p450 pb-1, p450 mp-4, s-mephenytoin 4-hyd p-450mp. Engineered: yes. Mutation: yes
Source: Homo sapiens. Human. Organism_taxid: 9606. Gene: cyp2c9. Expressed in: escherichia coli. Expression_system_taxid: 562.
Biol. unit: Trimer (from PQS)
2.00Å     R-factor:   0.191     R-free:   0.236
Authors: M.R.Wester,J.K.Yano,G.A.Schoch,K.J.Griffin,C.D.Stout,E.F.Joh
Key ref:
M.R.Wester et al. (2004). The structure of human cytochrome P450 2C9 complexed with flurbiprofen at 2.0-A resolution. J Biol Chem, 279, 35630-35637. PubMed id: 15181000 DOI: 10.1074/jbc.M405427200
30-Oct-03     Release date:   15-Jun-04    
Go to PROCHECK summary

Protein chain
Pfam   ArchSchema ?
P11712  (CP2C9_HUMAN) -  Cytochrome P450 2C9
490 a.a.
455 a.a.*
Key:    PfamA domain  Secondary structure  CATH domain
* PDB and UniProt seqs differ at 1 residue position (black cross)

 Enzyme reactions 
   Enzyme class 1: E.C.  - (S)-limonene 6-monooxygenase.
[IntEnz]   [ExPASy]   [KEGG]   [BRENDA]
      Reaction: --(S)-limonene + NADPH + O2 = --trans-carveol + NADP+ + H2O
Bound ligand (Het Group name = FLP)
matches with 55.56% similarity
+ O(2)
= (-)-trans-carveol
+ NADP(+)
+ H(2)O
      Cofactor: Heme-thiolate
   Enzyme class 2: E.C.  - (S)-limonene 7-monooxygenase.
[IntEnz]   [ExPASy]   [KEGG]   [BRENDA]
      Reaction: --(S)-limonene + NADPH + O2 = --perillyl alcohol + NADP+ + H2O
Bound ligand (Het Group name = FLP)
matches with 55.56% similarity
+ O(2)
= (-)-perillyl alcohol
+ NADP(+)
+ H(2)O
      Cofactor: Heme-thiolate
   Enzyme class 3: E.C.  - (R)-limonene 6-monooxygenase.
[IntEnz]   [ExPASy]   [KEGG]   [BRENDA]

      Reaction: +-(R)-limonene + NADPH + O2 = +-trans-carveol + NADP+ + H2O
Bound ligand (Het Group name = FLP)
matches with 55.56% similarity
+ O(2)
= (+)-trans-carveol
+ NADP(+)
+ H(2)O
      Cofactor: Heme-thiolate
Note, where more than one E.C. class is given (as above), each may correspond to a different protein domain or, in the case of polyprotein precursors, to a different mature protein.
Molecule diagrams generated from .mol files obtained from the KEGG ftp site
 Gene Ontology (GO) functional annotation 
  GO annot!
  Cellular component     membrane   5 terms 
  Biological process     small molecule metabolic process   15 terms 
  Biochemical function     (R)-limonene 6-monooxygenase activity     12 terms  


DOI no: 10.1074/jbc.M405427200 J Biol Chem 279:35630-35637 (2004)
PubMed id: 15181000  
The structure of human cytochrome P450 2C9 complexed with flurbiprofen at 2.0-A resolution.
M.R.Wester, J.K.Yano, G.A.Schoch, C.Yang, K.J.Griffin, C.D.Stout, E.F.Johnson.
The structure of human P450 2C9 complexed with flurbiprofen was determined to 2.0 A by x-ray crystallography. In contrast to other structurally characterized P450 2C enzymes, 2C5, 2C8, and a 2C9 chimera, the native catalytic domain of P450 2C9 differs significantly in the conformation of the helix F to helix G region and exhibits an extra turn at the N terminus of helix A. In addition, a distinct conformation of the helix B to helix C region allows Arg-108 to hydrogen bond with Asp-293 and Asn-289 on helix I and to interact directly with the carboxylate of flurbiprofen. These interactions position the substrate for regioselective oxidation in a relatively large active site cavity and are likely to account for the high catalytic efficiency exhibited by P450 2C9 for the regioselective oxidation of several anionic non-steroidal anti-inflammatory drugs. The structure provides a basis for interpretation of a number of observations regarding the substrate selectivity of P450 2C9 and the observed effects of mutations on catalysis.
  Selected figure(s)  
Figure 2.
FIG. 2. Comparison of the 1R9O [PDB] structure (cyan) with the 1OG5 [PDB] structure (gray). Ribbons depict the C -trace of the two structures near the N-terminal end of helix A. Helices F' and G' are not evident in the 1R9O [PDB] structure, which exhibits a more extended conformation of the region between helices F and G and a longer helix A. A divergent stereo view is shown.
Figure 5.
FIG. 5. Amino acid side chains residing within 5 Å of flurbiprofen. Amino acid side chains, a glycerol, and flurbiprofen are rendered as stick figures with carbons colored white except in flurbiprofen, where carbons are colored cyan. Oxygen, nitrogen, sulfur, and fluorine are colored red, blue, yellow, and purple, respectively. For reference, the heme is shown as a stick figure colored salmon, and a portion of helix I is rendered as a ribbon with the position of Gly-296 shown. Water molecules 600, 819, and 842 are rendered as red spheres. A divergent stereo view is shown.
  The above figures are reprinted by permission from the ASBMB: J Biol Chem (2004, 279, 35630-35637) copyright 2004.  
  Figures were selected by an automated process.  

Literature references that cite this PDB file's key reference

  PubMed id Reference
21356265 H.Banu, N.Renuka, and G.Vasanthakumar (2011).
Reduced catalytic activity of human CYP2C9 natural alleles for gliclazide: molecular dynamics simulation and docking studies.
  Biochimie, 93, 1028-1036.  
20848147 H.Jiang, F.Zhong, L.Sun, W.Feng, Z.X.Huang, and X.Tan (2011).
Structural and functional insights into polymorphic enzymes of cytochrome P450 2C8.
  Amino Acids, 40, 1195-1204.  
21482471 V.P.Androutsopoulos, A.Papakyriakou, D.Vourloumis, and D.A.Spandidos (2011).
Comparative CYP1A1 and CYP1B1 substrate and inhibitor profile of dietary flavonoids.
  Bioorg Med Chem, 19, 2842-2849.  
21058395 W.Li, J.Shen, G.Liu, Y.Tang, and T.Hoshino (2011).
Exploring coumarin egress channels in human cytochrome P450 2A6 by random acceleration and steered molecular dynamics simulations.
  Proteins, 79, 271-281.  
20361237 A.Tarcsay, R.Kiss, and G.M.Keseru (2010).
Site of metabolism prediction on cytochrome P450 2C9: a knowledge-based docking approach.
  J Comput Aided Mol Des, 24, 399-408.  
20839301 E.Sano, W.Li, H.Yuki, X.Liu, T.Furihata, K.Kobayashi, K.Chiba, S.Neya, and T.Hoshino (2010).
Mechanism of the decrease in catalytic activity of human cytochrome P450 2C9 polymorphic variants investigated by computational analysis.
  J Comput Chem, 31, 2746-2758.  
21038340 G.Rossato, B.Ernst, M.Smiesko, M.Spreafico, and A.Vedani (2010).
Probing small-molecule binding to cytochrome P450 2D6 and 2C9: An in silico protocol for generating toxicity alerts.
  ChemMedChem, 5, 2088-2101.  
19878193 H.Sun, and D.O.Scott (2010).
Structure-based drug metabolism predictions for drug design.
  Chem Biol Drug Des, 75, 3.  
20498847 K.M.Manoj, A.Baburaj, B.Ephraim, F.Pappachan, P.P.Maviliparambathu, U.K.Vijayan, S.V.Narayanan, K.Periasamy, E.A.George, and L.T.Mathew (2010).
Explaining the atypical reaction profiles of heme enzymes with a novel mechanistic hypothesis and kinetic treatment.
  PLoS One, 5, e10601.  
20967245 K.M.Manoj, S.K.Gade, and L.Mathew (2010).
Cytochrome P450 reductase: a harbinger of diffusible reduced oxygen species.
  PLoS One, 5, e13272.  
20877134 L.Quintieri, S.Bortolozzo, S.Stragliotto, S.Moro, M.Pavanetto, A.Nassi, P.Palatini, and M.Floreani (2010).
Flavonoids diosmetin and hesperetin are potent inhibitors of cytochrome P450 2C9-mediated drug metabolism in vitro.
  Drug Metab Pharmacokinet, 25, 466-476.  
20013305 L.Sun, Z.H.Wang, F.Y.Ni, X.S.Tan, and Z.X.Huang (2010).
The role of Ile476 in the structural stability and substrate binding of human cytochrome P450 2C8.
  Protein J, 29, 32-43.  
20361239 R.J.Unwalla, J.B.Cross, S.Salaniwal, A.D.Shilling, L.Leung, J.Kao, and C.Humblet (2010).
Using a homology model of cytochrome P450 2D6 to predict substrate site of metabolism.
  J Comput Aided Mol Des, 24, 237-256.  
20446763 T.C.Pochapsky, S.Kazanis, and M.Dang (2010).
Conformational plasticity and structure/function relationships in cytochromes P450.
  Antioxid Redox Signal, 13, 1273-1296.  
19258521 C.M.Mosher, G.Tai, and A.E.Rettie (2009).
CYP2C9 amino acid residues influencing phenytoin turnover and metabolite regio- and stereochemistry.
  J Pharmacol Exp Ther, 329, 938-944.  
19728720 D.Fishelovitch, S.Shaik, H.J.Wolfson, and R.Nussinov (2009).
Theoretical characterization of substrate access/exit channels in the human cytochrome P450 3A4 enzyme: involvement of phenylalanine residues in the gating mechanism.
  J Phys Chem B, 113, 13018-13025.  
18838506 J.M.Hutzler, L.M.Balogh, M.Zientek, V.Kumar, and T.S.Tracy (2009).
Mechanism-based inactivation of cytochrome P450 2C9 by tienilic acid and (+/-)-suprofen: a comparison of kinetics and probe substrate selection.
  Drug Metab Dispos, 37, 59-65.  
19171677 M.Yang, J.L.Kabulski, L.Wollenberg, X.Chen, M.Subramanian, T.S.Tracy, D.Lederman, P.M.Gannett, and N.Wu (2009).
Electrocatalytic drug metabolism by CYP2C9 bonded to a self-assembled monolayer-modified electrode.
  Drug Metab Dispos, 37, 892-899.  
19251817 N.M.DeVore, B.D.Smith, J.L.Wang, G.H.Lushington, and E.E.Scott (2009).
Key residues controlling binding of diverse ligands to human cytochrome P450 2A enzymes.
  Drug Metab Dispos, 37, 1319-1327.  
19265398 S.Balaz (2009).
Modeling kinetics of subcellular disposition of chemicals.
  Chem Rev, 109, 1793-1899.  
19397311 S.C.Gay, L.Sun, K.Maekawa, J.R.Halpert, and C.D.Stout (2009).
Crystal structures of cytochrome P450 2B4 in complex with the inhibitor 1-biphenyl-4-methyl-1H-imidazole: ligand-induced structural response through alpha-helical repositioning.
  Biochemistry, 48, 4762-4771.
PDB codes: 3g5n 3g93
19053752 C.C.Peng, J.L.Cape, T.Rushmore, G.J.Crouch, and J.P.Jones (2008).
Cytochrome P450 2C9 type II binding studies on quinoline-4-carboxamide analogues.
  J Med Chem, 51, 8000-8011.  
18922023 C.M.Mosher, M.A.Hummel, T.S.Tracy, and A.E.Rettie (2008).
Functional analysis of phenylalanine residues in the active site of cytochrome P450 2C9.
  Biochemistry, 47, 11725-11734.  
18721112 D.F.Lewis, and Y.Ito (2008).
Human cytochromes P450 in the metabolism of drugs: new molecular models of enzyme-substrate interactions.
  Expert Opin Drug Metab Toxicol, 4, 1181-1186.  
19040328 D.R.Davydov, and J.R.Halpert (2008).
Allosteric P450 mechanisms: multiple binding sites, multiple conformers or both?
  Expert Opin Drug Metab Toxicol, 4, 1523-1535.  
18622598 E.M.Isin, and F.P.Guengerich (2008).
Substrate binding to cytochromes P450.
  Anal Bioanal Chem, 392, 1019-1030.  
18484912 E.Stjernschantz, N.P.Vermeulen, and C.Oostenbrink (2008).
Computational prediction of drug binding and rationalisation of selectivity towards cytochromes P450.
  Expert Opin Drug Metab Toxicol, 4, 513-527.  
18606741 G.Tai, L.J.Dickmann, N.Matovic, J.J.DeVoss, E.M.Gillam, and A.E.Rettie (2008).
Re-engineering of CYP2C9 to probe acid-base substrate selectivity.
  Drug Metab Dispos, 36, 1992-1997.  
18950282 I.A.Pikuleva (2008).
Cholesterol-metabolizing cytochromes P450: implications for cholesterol lowering.
  Expert Opin Drug Metab Toxicol, 4, 1403-1414.  
18669584 J.D'Agostino, X.Zhang, H.Wu, G.Ling, S.Wang, Q.Y.Zhang, F.Liu, and X.Ding (2008).
Characterization of CYP2A13*2, a variant cytochrome P450 allele previously found to be associated with decreased incidences of lung adenocarcinoma in smokers.
  Drug Metab Dispos, 36, 2316-2323.  
18026129 J.D.Maréchal, C.A.Kemp, G.C.Roberts, M.J.Paine, C.R.Wolf, and M.J.Sutcliffe (2008).
Insights into drug metabolism by cytochromes P450 from modelling studies of CYP2D6-drug interactions.
  Br J Pharmacol, 153, S82-S89.  
18976212 K.N.Myasoedova (2008).
New findings in studies of cytochromes P450.
  Biochemistry (Mosc), 73, 965-969.  
18485885 M.A.Hummel, P.M.Gannett, J.Aguilar, and T.S.Tracy (2008).
Substrate proton to heme distances in CYP2C9 allelic variants and alterations by the heterotropic activator, dapsone.
  Arch Biochem Biophys, 475, 175-183.  
18621681 N.Mast, M.A.White, I.Bjorkhem, E.F.Johnson, C.D.Stout, and I.A.Pikuleva (2008).
Crystal structures of substrate-bound and substrate-free cytochrome P450 46A1, the principal cholesterol hydroxylase in the brain.
  Proc Natl Acad Sci U S A, 105, 9546-9551.
PDB codes: 2q9f 2q9g
18214952 R.Minai, Y.Matsuo, H.Onuki, and H.Hirota (2008).
Method for comparing the structures of protein ligand-binding sites and application for predicting protein-drug interactions.
  Proteins, 72, 367-381.  
18004755 W.Li, Y.Tang, H.Liu, J.Cheng, W.Zhu, and H.Jiang (2008).
Probing ligand binding modes of human cytochrome P450 2J2 by homology modeling, molecular dynamics simulation, and flexible molecular docking.
  Proteins, 71, 938-949.  
18511451 Y.Wada, M.Mitsuda, Y.Ishihara, M.Watanabe, M.Iwasaki, and S.Asahi (2008).
Important amino acid residues that confer CYP2C19 selective activity to CYP2C9.
  J Biochem, 144, 323-333.  
17207766 A.J.Annalora, E.Bobrovnikov-Marjon, R.Serda, A.Pastuszyn, S.E.Graham, C.B.Marcus, and J.L.Omdahl (2007).
Hybrid homology modeling and mutational analysis of cytochrome P450C24A1 (CYP24A1) of the Vitamin D pathway: insights into substrate specificity and membrane bound structure-function.
  Arch Biochem Biophys, 460, 262-273.  
17534532 A.W.Munro, H.M.Girvan, and K.J.McLean (2007).
Variations on a (t)heme--novel mechanisms, redox partners and catalytic functions in the cytochrome P450 superfamily.
  Nat Prod Rep, 24, 585-609.  
17311370 C.W.Locuson, P.M.Gannett, R.Ayscue, and T.S.Tracy (2007).
Use of simple docking methods to screen a virtual library for heteroactivators of cytochrome P450 2C9.
  J Med Chem, 50, 1158-1165.  
17559204 D.R.McMasters, R.A.Torres, S.J.Crathern, D.L.Dooney, R.B.Nachbar, R.P.Sheridan, and K.R.Korzekwa (2007).
Inhibition of recombinant cytochrome P450 isoforms 2D6 and 2C9 by diverse drug-like molecules.
  J Med Chem, 50, 3205-3213.  
17827781 E.Kamiyama, Y.Yoshigae, A.Kasuya, M.Takei, A.Kurihara, and T.Ikeda (2007).
Inhibitory effects of angiotensin receptor blockers on CYP2C9 activity in human liver microsomes.
  Drug Metab Pharmacokinet, 22, 267-275.  
17585868 G.I.Lepesheva, M.Seliskar, C.G.Knutson, N.V.Stourman, D.Rozman, and M.R.Waterman (2007).
Conformational dynamics in the F/G segment of CYP51 from Mycobacterium tuberculosis monitored by FRET.
  Arch Biochem Biophys, 464, 221-227.  
17686967 L.Wei, C.W.Locuson, and T.S.Tracy (2007).
Polymorphic variants of CYP2C9: mechanisms involved in reduced catalytic activity.
  Mol Pharmacol, 72, 1280-1288.  
17160453 M.Morant, G.A.Schoch, P.Ullmann, T.Ertunç, D.Little, C.E.Olsen, M.Petersen, J.Negrel, and D.Werck-Reichhart (2007).
Catalytic activity, duplication and evolution of the CYP98 cytochrome P450 family in wheat.
  Plant Mol Biol, 63, 1.  
17054666 N.K.Zgheib, R.F.Frye, T.S.Tracy, M.Romkes, and R.A.Branch (2007).
Evaluation of flurbiprofen urinary ratios as in vivo indices for CYP2C9 activity.
  Br J Clin Pharmacol, 63, 477-487.  
17705402 P.Lafite, F.André, D.C.Zeldin, P.M.Dansette, and D.Mansuy (2007).
Unusual regioselectivity and active site topology of human cytochrome P450 2J2.
  Biochemistry, 46, 10237-10247.  
17470359 P.Lafite, S.Dijols, D.C.Zeldin, P.M.Dansette, and D.Mansuy (2007).
Selective, competitive and mechanism-based inhibitors of human cytochrome P450 2J2.
  Arch Biochem Biophys, 464, 155-168.  
17539741 T.M.Polasek, and J.O.Miners (2007).
In vitro approaches to investigate mechanism-based inactivation of CYP enzymes.
  Expert Opin Drug Metab Toxicol, 3, 321-329.  
17960328 T.Polgár, D.K.Menyhárd, and G.M.Keseru (2007).
Effective virtual screening protocol for CYP2C9 ligands using a screening site constructed from flurbiprofen and S-warfarin pockets.
  J Comput Aided Mol Des, 21, 539-548.  
16863464 A.K.Daly, and B.P.King (2006).
Contribution of CYP2C9 to variability in vitamin K antagonist metabolism.
  Expert Opin Drug Metab Toxicol, 2, 3.  
16639745 A.Seifert, S.Tatzel, R.D.Schmid, and J.Pleiss (2006).
Multiple molecular dynamics simulations of human p450 monooxygenase CYP2C9: the molecular basis of substrate binding and regioselectivity toward warfarin.
  Proteins, 64, 147-155.  
16700545 J.T.Pearson, J.J.Hill, J.Swank, N.Isoherranen, K.L.Kunze, and W.M.Atkins (2006).
Surface plasmon resonance analysis of antifungal azoles binding to CYP3A4 with kinetic resolution of multiple binding orientations.
  Biochemistry, 45, 6341-6353.  
17047872 J.Zurek, N.Foloppe, J.N.Harvey, and A.J.Mulholland (2006).
Mechanisms of reaction in cytochrome P450: Hydroxylation of camphor in P450cam.
  Org Biomol Chem, 4, 3931-3937.  
16788382 K.Maekawa, H.Fukushima-Uesaka, M.Tohkin, R.Hasegawa, H.Kajio, N.Kuzuya, K.Yasuda, M.Kawamoto, N.Kamatani, K.Suzuki, T.Yanagawa, Y.Saito, and J.Sawada (2006).
Four novel defective alleles and comprehensive haplotype analysis of CYP2C9 in Japanese.
  Pharmacogenet Genomics, 16, 497-514.  
16637647 K.P.Ravindranathan, E.Gallicchio, R.A.Friesner, A.E.McDermott, and R.M.Levy (2006).
Conformational equilibrium of cytochrome P450 BM-3 complexed with N-palmitoylglycine: a replica exchange molecular dynamics study.
  J Am Chem Soc, 128, 5786-5791.  
16892339 M.A.Lill, M.Dobler, and A.Vedani (2006).
Prediction of small-molecule binding to cytochrome P450 3A4: flexible docking combined with multidimensional QSAR.
  ChemMedChem, 1, 73-81.  
16954191 M.Ekroos, and T.Sjögren (2006).
Structural basis for ligand promiscuity in cytochrome P450 3A4.
  Proc Natl Acad Sci U S A, 103, 13682-13687.
PDB codes: 2j0c 2j0d 2v0m
16793528 Groot (2006).
Designing better drugs: predicting cytochrome P450 metabolism.
  Drug Discov Today, 11, 601-606.  
16802783 P.M.Gannett, J.Kabulski, F.A.Perez, Z.Liu, D.Lederman, C.W.Locuson, R.R.Ayscue, N.M.Thomsen, and T.S.Tracy (2006).
Preparation, characterization, and substrate metabolism of gold-immobilized cytochrome P450 2C9.
  J Am Chem Soc, 128, 8374-8375.  
16863447 T.Herz, K.Wolf, J.Kraus, and B.Kramer (2006).
4SCan/vADME: intelligent library screening as a shortcut from hits to lead compounds.
  Expert Opin Drug Metab Toxicol, 2, 471-484.  
16862439 V.R.Dodhia, A.Fantuzzi, and G.Gilardi (2006).
Engineering human cytochrome P450 enzymes into catalytically self-sufficient chimeras using molecular Lego.
  J Biol Inorg Chem, 11, 903-916.  
15822186 A.E.Rettie, and J.P.Jones (2005).
Clinical and toxicological relevance of CYP2C9: drug-drug interactions and pharmacogenetics.
  Annu Rev Pharmacol Toxicol, 45, 477-494.  
16052607 C.Sun, J.R.Huth, and P.J.Hajduk (2005).
NMR in pharmacokinetic and pharmacodynamic profiling.
  Chembiochem, 6, 1592-1600.  
15970795 G.Tai, F.Farin, M.J.Rieder, A.W.Dreisbach, D.L.Veenstra, C.L.Verlinde, and A.E.Rettie (2005).
In-vitro and in-vivo effects of the CYP2C9*11 polymorphism on warfarin metabolism and dose.
  Pharmacogenet Genomics, 15, 475-481.  
16059671 J.M.Kriegl, T.Arnhold, B.Beck, and T.Fox (2005).
A support vector machine approach to classify human cytochrome P450 3A4 inhibitors.
  J Comput Aided Mol Des, 19, 189-201.  
16224454 L.C.Wienkers, and T.G.Heath (2005).
Predicting in vivo drug interactions from in vitro drug discovery data.
  Nat Rev Drug Discov, 4, 825-833.  
  15955872 M.A.Hummel, C.W.Locuson, P.M.Gannett, D.A.Rock, C.M.Mosher, A.E.Rettie, and T.S.Tracy (2005).
CYP2C9 genotype-dependent effects on in vitro drug-drug interactions: switching of benzbromarone effect from inhibition to activation in the CYP2C9.3 variant.
  Mol Pharmacol, 68, 644-651.  
16272806 M.Hashida (2005).
[In-silico prediction of pharmacokinetic properties]
  Yakugaku Zasshi, 125, 853-861.  
15855725 M.Tsuda-Tsukimoto, Y.Ogasawara, and T.Kume (2005).
Role of human liver cytochrome P450 2C9 in the metabolism of a novel alpha4beta1/alpha4beta7 dual antagonist, TR-14035.
  Drug Metab Pharmacokinet, 20, 127-134.  
16308280 Y.Guo, Y.Wang, D.Si, P.J.Fawcett, D.Zhong, and H.Zhou (2005).
Catalytic activities of human cytochrome P450 2C9*1, 2C9*3 and 2C9*13.
  Xenobiotica, 35, 853-861.  
The most recent references are shown first. Citation data come partly from CiteXplore and partly from an automated harvesting procedure. Note that this is likely to be only a partial list as not all journals are covered by either method. However, we are continually building up the citation data so more and more references will be included with time. Where a reference describes a PDB structure, the PDB codes are shown on the right.