Accurate biochemical knowledge starting with precise structure-based criteria for molecular identity

Transcription

1 1 NCBO Seminar Series::Michel Dumontier Accurate biochemical knowledge starting with precise structure-based criteria for molecular identity Michel Dumontier, Ph.D. Assistant Professor of Bioinformatics Department of Biology, School of Computer Science Institute of Biochemistry, Ottawa Institute of Systems Biology Carleton University

2 2 NCBO Seminar Series::Michel Dumontier Problem Statement (I) Although biochemical events can be described with reference to specific chemical substances, we may want to describe them at finer/grainier levels of (mereological) granularity. residue : post translational modification collection of residues : motif/domain/interaction site atom : atomic interactions, catalytic mechanism collection of atoms : binding/catalytic site, interaction This requires identifiers for parts, regions (contiguous and non-contiguous), aggregates/complexes. However, we do not (AFAIK) have a precise (reproducible) methodology to automatically generate these!

3 Bio2RDF: 2.3B triples of SPARQLaccessible linked biological data! Chemical Parts!

4 4 NCBO Seminar Series::Michel Dumontier Case Study: HIF1α Hypoxia-Inducible Factor 1, alpha chain (uniprot:q16665) Master transcriptional regulator of the adaptive response to hypoxia Under normoxic conditions, HIF1α is hydroxylated on Pro-402 and Pro-564 in the oxygen-dependent degradation domain (ODD) by EGLN1/PHD1 and EGLN2/PHD2. EGLN3/PHD3 has also been shown to hydroxylate Pro-564. The hydroxylated prolines promote interaction with VHL, initiating rapid ubiquitination and subsequent proteasomal degradation. Context Dependent Behavior a) Normoxic Conditions b) Hypoxic Conditions Multiple hydroxylations Part of a domain Selective interaction with parts The part is the agent in the process

5 5 NCBO Seminar Series::Michel Dumontier Are these the same? HIF1α au naturel HIF1α HIF1α HIF1α HIF1α & HIF1α L400A & L397A

6 NO!!!! These are structurally different Each exhibits distinct functionality! Yet most databases (Uniprot/Genbank) don t have separate identifiers for them Reactome has an internal identifier for referring to different forms, but links to Uniprot entries and doesn t provide an explicit description of the structure that it corresponds to! 6 NCBO Seminar Series::Michel Dumontier

7 So We have a clear need for being able to refer to distinct biochemical entities, based at least on their structure. We also need to refer to arbitrary structural parts. Should we generate all the combinations a priori??? NO!! Should we be able to automatically generate the identifier from the structural attributes? -> YES!!! Should we semantically annotate (manually or otherwise) those forms known to be involved in specific processes??? -> YES!!! What identifiers are unique for a given structure? 7 NCBO Seminar Series::Michel Dumontier

8 8 NCBO Seminar Series::Michel Dumontier InChI IUPAC International Chemical Identifier (InChI) A data string that provides 1. the structure of a chemical compound 2. the convention for drawing the structure Different compounds must have different identifiers. Several attributes can be used to distinguish one compound from another. chemical graph (connection table) Formula Atom type (only some atoms explicit) Bond type Stereochemistry Mobile/fixed H-bonds (tautomers) Isotopic composition Atomic charge

9 9 NCBO Seminar Series::Michel Dumontier (S)-Glutamic Acid InChI= {version}1 /{formula}c5h9no4 /c{connections}6-3(5(9)10)1-2-4(7)8 /h{h_atoms}3h,1-2,6h2,(h,7,8)(h,9,10) /p{protons}+1 /t{stereo:sp3}3- /m{stereo:sp3:inverted}0 /s{stereo:type (1=abs, 2=rel, 3=rac)}1 /i{isotopic:atoms}4+1

10 10 NCBO Seminar Series::Michel Dumontier More non-core info captured in AuxInfo string... AuxInfo=1/1/N:5,6,2,7,1,4,8,9,10,11/E:(7,8)(9,10)/it:im/I:/E:m/rA:11nCCHN+CCC.i13OOOO/rB:s1;N2;P2;s2;s5;s6;s7;d7;d1;s1; /rc:6.1671, ,0;7.0125, ,0;6.4113, ,0;7.6089, ,0;7.8578, ,0;8.891, ,0;9.7363, ,0;9.7316, ,0; , ,0;5.0071, ,0;6.1624, ,0; AuxInfo= {version}1 /{normalization_type}1 /N:{original_atom_numbers}5,6,2,7,1,4,8,9,10,11 /E:{atom_equivalence}(7,8)(9,10) /it:{abs_stereo_inverted:sp3}im /I:{isotopic:original_atom_numbers} /E:{isotopic:atom_equivalence}m /ra:{reversibility:atoms}11ncchn+ccc.i13oooo /rb:{reversibility:bonds}s1;n2;p2;s2;s5;s6;s7;d7;d1;s1; /rc:{reversibility:xyz}6.1671, ,0;7.0125, ,0;6.4113, ,0;7.6089, ,0;7.8578, ,0;8.891, ,0;9.7363, ,0;9.7316, ,0; , ,0;5.0071, ,0;6.1624, ,0;

11 11 NCBO Seminar Series::Michel Dumontier So... InChi a really just a cryptic data identifier Clever software required to gradually build the chemical identifiers in a series of well-defined steps normalization, canonicalization then serialization Humans can t (easily) generate them nor can they easily understand them. But that s OK. It s not (user) extensible. But that s OK.

12 12 NCBO Seminar Series::Michel Dumontier InCHI for Proteins??? Possible... but a 1000 residue protein would contain ~15,000 atoms on average... OpenBabel seemed to struggle with anything over 100 residues Maybe needs some performance tweaking? Size of the string will be enormous We can use InChiKeys (SHA1 hash), but then we need to provide a you-submit-inchi, we-store-both and they-look-it-up service. Modularize InChI construction for (linear) polymers? Make InChi strings for each residue, and concatenate rename the atoms according to the residue position We still need to translate the InChi string...

13 OpenBabel IUPAC SMILES InCHI 6-(hydroxymethyl)oxane-2,3,4,5-tetrol OR (2R,3R,4S,5R,6R)-6 -(hydroxymethyl)tetrahydro -2H-pyran-2,3,4,5-tetraol InChI=1/C6H12O6/c (8)4(9)5(10)6(11)12-2/h2-11H,1H2/t2-,3-,4+,5-,6+/m1/s1 α-d-glucose SDF CML

14 14 NCBO Seminar Series::Michel Dumontier OWL Has Explicit Semantics Can therefore be used to capture knowledge in a machine understandable way

15 Chemical Ontology Chemical Knowledge for the Semantic Web. Mykola Konyk, Alexander De Leon, and Michel Dumontier. LNBI : Data Integration in the Life Sciences (DILS2008). Evry. France.

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17 Describing chemical functional groups in OWL-DL for the classification of chemical compounds methyl group hydroxyl group Ethanol Knowledge of functional groups is important in chemical synthesis, pharmaceutical design and lead optimization. Functional groups describe chemical reactivity in terms of atoms and their connectivity, and exhibits characteristic chemical behavior when present in a compound. N Villanueva-Rosales, MDumontier OWLED, Innsbruck, Austria. 17 NCBO Seminar Series::Michel Dumontier

18 18 NCBO Seminar Series::Michel Dumontier Describing Functional Groups in DL R group R O H HydroxylGroup: CarbonGroup that (hassinglebondwith some (OxygenAtom that hassinglebondwith some HydrogenAtom)

19 19 NCBO Seminar Series::Michel Dumontier Fully Classified Ontology 35 FG

20 20 NCBO Seminar Series::Michel Dumontier And, we define certain compounds Alcohol: OrganicCompound that (haspart some HydroxylGroup)

21 21 NCBO Seminar Series::Michel Dumontier Organic Compound Ontology 28 OC

22 Question Answering Query PubChem, DrugBank and dbpedia* * Requires import of relevant URIs 22 NCBO Seminar Series::Michel Dumontier

23 23 NCBO Seminar Series::Michel Dumontier But... Molecules represented as individuals because OWL-DL only allows tree-like class descriptions No variable binding (e.g.?x)... no cyclic molecule/functional group descriptions at the class level Boris Motik et al has a proposal for Description Graphs, Robert Stevens & Duncan Hull trying it out for chemical representation...

24 24 NCBO Seminar Series::Michel Dumontier Identifiers for Atoms Atom identifiers can be consistently retrieved from the OpenBabel model. Canonical numbering means we can reliably refer to a specific region rather than a (possibly degenerate) sub-graph match. In our plugin, URI component naming was based on the assigned molecule identifier e.g. pubchemid#an, where N is the number Use InChiKey as base? e.g. InChiKey#aN

25 25 NCBO Seminar Series::Michel Dumontier What about identifiers for collection of atoms? Potentially useful in describing residues, PTMs, binding sites, etc. Is the lack of connectivity sufficient? Contiguous: ranges (an-an) enumerations (an,an,an) Non-contiguous: Combination of ranges, enumerations?

26 26 NCBO Seminar Series::Michel Dumontier Can we reuse our positional nomenclature for residues? Residues are generally referred to by their absolute position in the biopolymer sequence. e.g. X on Protein Y InChiKey#a50-a65 owl:sameas InChiKey#r5 InChiKey#r5_a1-r5_a15 owl:sameas InChiKey#r5 Collection of Residues might follow the same rules as a Collection of Atoms. Useful for defining domains, motifs, etc

27 27 NCBO Seminar Series::Michel Dumontier An Alternative Scheme We already have a simplified representation for biopolymers... Canonical sequence is represented by a string of single letter characters DNA: ACGT RNA: ACGU Proteins: 20 amino acids (not B,J,O,U,X,Z) Modifications can be referred to with ChEBI/PSI-MOD ontology (e.g. Prolyl hydroxylated 402) Each (modified) residue must have its InChi description so as to capture explicit structural deviations (de-protonation, etc)

28 28 NCBO Seminar Series::Michel Dumontier PSI-MOD contains modified residues with links to structural descriptions

29 29 NCBO Seminar Series::Michel Dumontier But what if we have a modification that isn t contained in the ontology! No problem... define your own term, with the corresponding structural description (InChi, SMILES), and add to an ontology document... If you re using OWL, you can add the import statement and publish it. And, of course, you should submit it to the appropriate ontology development teams. (and later make it equivalent to)

30 While we re at it, we could extend our expressive capability to match that of OWL: Specification Exactly X Only Minimum : At least mod1@posx Combination: mod1@posx AND mod2@posy, X!= Y Possibilities/Uncertainty: (mod1 OR Exclusion: not posx 30 NCBO Seminar Series::Michel Dumontier

31 31 NCBO Seminar Series::Michel Dumontier So what if... we describe the structural features of the molecule with OWL (sequence + PTMs), and generate an identifier from one of its serializations (RDF/XML?) that way we have the explicit description as the identifier in a form that is compatible with the semantic web.

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33 33 NCBO Seminar Series::Michel Dumontier Uniprot example revisited. Under normoxic conditions, HIF1α is hydroxylated on Pro-402 and Pro-564 in the oxygen-dependent degradation domain (ODD) by EGLN1/PHD1 and EGLN2/PHD2. The hydroxylated prolines promote interaction with VHL, initiating rapid ubiquitination and subsequent proteasomal degradation :1 (HIF1α) :2 (HIF1α + P402hyd) :3 (HIF1α + P564hyd) :4 (HIF1α + P402hyd + P564hyd) :5 (EGLN1) :6 (VHL) :A rdfs:subclassof :Hydroxylation :A hasparticipant (:0#r402 and :Substrate) :A hasparticipant (:1#r402 and :Product) :A hasparticipant (:5 and :Enzyme) :B rdfs:subclassof :Interaction :B :hasparticipant (:2#r402 or :3#r564 or :4#r402,r564) :B :hasparticipant (:6) Please ignore the made up short-hand syntax!

34 34 NCBO Seminar Series::Michel Dumontier Infering Protein Participation OWL Role Chain hasparticipant o ispartof -> hasparticipant if process has the part as a participant, then the whole is also a participant :A rdfs:subclassof :Hydroxylation :A hasparticipant (:0#r402 and :Substrate) :A hasparticipant (:1#r402 and :Product) :0#r402 :ispartof :0 :1#r402 :ispartof :1 :A hasparticipant :0 :A hasparticipant :1

35 35 NCBO Seminar Series::Michel Dumontier Contextual, but non-structural considerations in identifier generation? Chemical? ph? Temperature? Environment (in vitro, in vivo, in silico)? Biological? Species? mrna/gene from which it was transcribed/encoded? Indirect Relationships? Point & Multiple Mutations? Alternative Splice Variants? Sequence Similarity?

36 36 NCBO Seminar Series::Michel Dumontier Summary We need a precise method to generate identifiers for biopolymers and arbitrary sets of their parts. Consistent identifier generation will allow anybody to specify findings according to the biopolymers for which it was observed, whether it exists in a database or not, and will allow us to link biochemical knowledge at finer levels of granularity. (at least) two identifier schemes were put forward to initiate discussion, with the goal of setting a standard naming convention.

37 dumontierlab.com Special thanks to PhD Student Leonid Chepelev for insightful discussions semanticscience.org 37 NCBO Seminar Series::Michel Dumontier