Protein Struktur (optional, flexible)

Transcription

1 Protein Struktur (optional, flexible) 22/10/2009 [ 1 ] Andrew Torda, Wintersemester 2009 / 2010, AST nur für Informatiker, Mathematiker,.. 26 kt, 3 ov 2009

2 Proteins - who cares? 22/10/2009 [ 2 ] Most important molecules in life? Ask the DA / RA people structural (keratin / hair) enzymes (catalysts) messengers (hormones) regulation (bind to other proteins, DA,..) industrial biosensors to washing powder receptors transporters ( 2, sugars, fats) anti-freeze

3 Proteins are easy 22/10/2009 [ 3 ] data (protein data bank, structures literature on function, interactions, structure software viewers, molecular dynamics simulators, docking,.. nomenclature and rules Proteins are not friendly one cannot take a sequence and predict structure /function data formats are full of surprises, mostly old formats data contains error and mistakes

4 Protein Rules 22/10/2009 [ 4 ] Physics /chemistry versus rules / dogma / beliefs / folklore Physics / Chemistry protein + water = set of interacting atoms can be calculated (not really) Rules (not quantified) proteins unfold if you heat them (exceptions?) if they contain lots of charged amino acids, they are soluble if they are more than 300 residues, they have more than one domain, proteins fold to a unique structure (could you prove this?) lowest free energy structure

5 Protein chemistry 22/10/2009 [ 5 ] Chemists / biochemists may sleep (quietly) Short version proteins are sets of building blocks (amino acids, residues, Reste) 20 types of residue chains of length few to 10 3 ( 100 or 200 typical) small ones (< 50) are peptides Longer version

6 myoglobin picture 2w6w Sizes 22/10/2009 [ 6 ] 1 Å = m or 0.1 nm structure size bond CH 1 Å CC 1.5 Å protein radius α-helix spacing C α i to C α i Å 5 ½ Å 3.8 Å

7 proteins are polymers Is it obvious what R is? 22/10/2009 [ 7 ] simple polymers A X B many times gives A X X X X X X X B example what kind of polymer would this give?

8 Why are proteins interesting polymers? 22/10/2009 [ 8 ] boring polymer gives uninteresting structures K for plastic bags, haushaltsfolie. ot nice regular structures.. What can we do to make things more protein like?

9 Giving proteins character 1 22/10/2009 [ 9 ] more complicated backbone with H-bond donor acceptor R R R basis of standard regular structures in proteins (secondary structure) R R repeating polymer unit: if this was all there was all proteins would be the same R

10 protein chemistry 22/10/2009 [ 10 ] amino acids (monomers) all look like: H 2 H C C H maybe H 3 + H C R C }- R sidechain α carbon or C α how can we construct specific structures? different kinds of "R" groups

11 Putting monomers together 22/10/2009 [ 11 ] H 2 H C R 1 H C H H H + 2 C C + R 2 H 2 H C R 3 C H H 2 H C C H H C C H H C H C R 1 R 2 R 3 protein synthesis story (biochemistry lectures) peptides and proteins < 30 or 40 residues = peptide > 30 or 40 residues = protein

12 side chain possibilities 22/10/2009 [ 12 ] big / small charged +, charged -, polar hydrophobic (not water soluble), polar interactions between sites A C C R W S T G B

13 Backbone and consequences 22/10/2009 [ 13 ] peptide bond is planar partial double bond character (resonance forms) shorter than other C- nearly always trans two bonds can rotate H 2 H C R 1 C H H C R 2 C H H C R 3 H C H 2 H C R 1 C H H C R 2 C H H C R 3 H C phi φ psi ψ

14 ramachandran plot can we rotate freely? no steric hindrance Ramachandran plot ψ psi 180 β α φ phi diagram from 22/10/2009 [ 14 ]

15 Backbone H bonds 22/10/2009 [ 15 ] oxygen is slightly negative H bond is polar δ + δ - δ + δ - C H H C H-bonds can be near or far in sequence fairly stable at room temperature

16 Secondary structure 22/10/2009 [ 16 ] regular structures using information so far rotate phi, psi angles so as to form H-bonds where possible do not force side chains to hit each other (steric clash) two common structures α-helix β-strand / sheet

17 diagram from Voet, D.J. and Voet, J.G, Biochemistry, Wiley, 2004 α helix 22/10/2009 [ 17 ] each C of residue i H-bonded to of i residues per turn 2 H-bonds per residue side chains well separated

18 β-sheet β-strand stretch out backbone and make H and C groups point out β-sheet join these strands together with H-bonds (2 H-bonds/residue) anti-parallel or parallel diagram from Voet, D.J. and Voet, J.G, Biochemistry, Wiley, /10/2009 [ 18 ]

19 After α-helix and β-sheet 22/10/2009 [ 19 ] do helices and sheets explain everything? no there is flexibility in the angles (look at plot) geometry is not perfectly defined there are local deviations and exceptions other common structures tighter helices some turns other structure coil, random, not named ψ psi φ phi

20 What determines secondary structure? 22/10/2009 [ 20 ] So far secondary structure pattern of H-bonding Almost all residues have H-bond acceptor and donor all could form α-helix or β-sheet? o Difference? sequence of side-chains overall folding Why else are sidechains important chemistry of proteins (interactions, catalysis) Fundamental dogma the sequence of sidechains determines the protein shape

21 Side chain properties 22/10/2009 [ 21 ] properties big / small neutral / polar / charged special ( ) example phenylalanine side chain looks like benzene (benzin) very insoluble benzene would rather interact with benzene than water what if you have phe-phe-phe poly-phe? does not happen in nature (can be made) would be insoluble not like a real peptide phe is a constituent of real proteins has a role

22 Taylor, W.R. (1986) J. Theor. Biol., Properties are not clear cut 22/10/2009 [ 22 ] You can be big / small, hydrophic / polar combinations are possible Do not memorise this figure

23 Sidechain interactions 22/10/2009 [ 23 ] ionic (if the sidechains have charge) hydrophobic (insoluble sidechains) H-bonds (some donors and acceptors) repulsive

24 Summary of amino acids (first dozen) 22/10/2009 [ 24 ]

25 summary of amino acids (second lot) 22/10/2009 [ 25 ]

26 Amino Acids by property 22/10/2009 [ 26 ] aromatic tryptophan phenylalanine tyrosine

27 rather hydrophobic 22/10/2009 [ 27 ] leucine isoleucine cysteine S methionine S alanine proline glycine valine

28 Polar 22/10/2009 [ 28 ] threonine serine glutamine asparagine

29 charged 22/10/2009 [ 29 ] histidine arginine lysine aspartate glutamate

30 Hydrophobicity how serious? 22/10/2009 [ 30 ] very serious, but simplified the lists above are ph dependent difficult to measure experimentally (some aspects) is hydrophobicity really defined? ther properties - size big small gly trp ala

31 ther properties chemistry / geometry 22/10/2009 [ 31 ] proline only one rotatable angle! peptide bond sometimes cis pro ramachandran plot

32 picture from Stryer, L, Biochemistry, WH Freeman, 1981 gly and cys 22/10/2009 [ 32 ] glycine no side chain can visit forbidden parts of phi-psi map (4 000 points here) cysteine forms covalent links with other cys

33 Summary so far 22/10/2009 [ 33 ] proteins are heteropolymers backbone forms α-helices and β-strands (and more) not sequence specific side-chains determine the pattern of secondary structure overall protein shape special amino acids cys (forms disulfide bridges) gly (can visit "forbidden" regions of ramachandran plot) pro (no H-bond donor) how many sequences can one have? nres 20

34 22/10/2009 [ 34 ] some rules are unavoidable omenclature Alanine Ala A Cysteine Cys C Aspartic acid Asp D Glutamic acid Glu E Phenylalanine Phe F Glycine Gly G Histidine His H Isoleucine Ile I Lysine Lys K Leucine Leu L Methionine Met M Asparagine Asn Proline Pro P Glutamine Gln Q Arginine Arg R Serine Ser S Threonine Thr T Valine Val V Tryptophan Trp W Tyrosine Tyr Y always write from to C terminal important convention

35 Definitions, primary, secondary 22/10/2009 [ 35 ] More definitions primary structure sequence of amino acids ACDF (ala cys asp phe ) secondary structure α-helix, β-sheet (+ few more) structure defined by local backbone tertiary structure how these units fold together coordinates of a protein

36 Protein structure general comments 22/10/2009 [ 36 ] primary, secondary, tertiary structure how real? primary/secondary well defined edges can blur supersecondary struct / tertiary

37 Representation 22/10/2009 [ 37 ] Ultimately, our representation of a structure ATM 1 ARG BPI 137 ATM 2 CA ARG BPI 138 ATM 3 C ARG BPI 139 ATM 4 ARG BPI 140 ATM 5 CB ARG BPI 141 ATM 6 CG ARG BPI 142 ATM 7 CD ARG BPI 143 ATM 8 E ARG BPI 144 ATM 9 CZ ARG BPI 145 ATM 10 H1 ARG BPI 146 ATM 11 H2 ARG BPI 147 ATM 12 PR BPI 148 ATM 13 CA PR BPI 149 ATM 14 C PR BPI 150 ATM 15 PR BPI 151 ATM 16 CB PR BPI 152 ATM 17 CG PR x, y, z coordinates BPI 153 ATM 18 CD PR BPI 154 ATM 19 ASP BPI 155 drawing the structure?

38 Representations 22/10/2009 [ 38 ] where are atoms? therapeutic binding which residues could be involved in interactions?

39 Representations 22/10/2009 [ 39 ] what is the surface? where could molecules fit?

40 Representations 22/10/2009 [ 40 ] colour surface by hydrophobicity

41 Representations 22/10/2009 [ 41 ] highlight / emphasise regular structures

42 Different levels of abstraction pictures from "Structural Bioinformatics", ed Bourne, PE and Weissig, H., Wiley ew York (2003) 22/10/2009 [ 42 ]

43 Atomistic For details where does a ligand bind? which interactions is a residue involved in? Ribbons verview shape number secondary struct elements symmetry strands helices pictures from "Structural Bioinformatics", ed Bourne, PE and Weissig, H., Wiley ew York (2003) 22/10/2009 [ 43 ]

44 More abstract no idea of real shape very quickly classify a protein example lots of serine proteases lots of different sequences all very similar at this level of abstraction pictures from "Structural Bioinformatics", ed Bourne, PE and Weissig, H., Wiley ew York (2003) 22/10/2009 [ 44 ]

45 Why does structure matter? 22/10/2009 [ 45 ] what residues can I change and preserve function? what is the reaction mechanism of an enzyme? what small molecules would bind and block the enzyme? is this protein the same shape as some other of known function? Where do structures come from? X-ray crystallography MR + a bit of small angle X-ray scattering, electron diffraction,

46 Atomic coordinates - warnings 22/10/2009 [ 46 ] remember the coordinate file? lots of problems atoms and residues missing numbering can be peculiar history suits fortran 66 (think columns) non-standard amino acids nucleotides, ligands accuracy ATM 1 ARG BPI 137 ATM 2 CA ARG BPI 138 ATM 3 C ARG BPI 139 ATM 4 ARG BPI 140 ATM 5 CB ARG BPI 141 ATM 6 CG ARG BPI 142 ATM 7 CD ARG BPI 143 ATM 8 E ARG BPI 144 ATM 9 CZ ARG BPI 145 ATM 10 H1 ARG BPI 146 ATM 11 H2 ARG BPI 147 ATM 12 PR BPI 148 ATM 13 CA PR BPI 149 ATM 14 C PR BPI 150 ATM 15 PR BPI 151 ATM 16 CB PR BPI 152 ATM 17 CG PR BPI 153 ATM 18 CD PR BPI 154 ATM 19 ASP BPI 155

47 resolution, precision, accuracy 22/10/2009 [ 47 ] coordinates what do they mean? random errors non-systematic / noise / uncertainty should be scattered around correct point from any measurement there are errors ± x x-ray crystallography has model for data uncertainty (probability) resolution (experimental) < 1 Å (good) > 5 Å (bad, but excusable monster structures)

48 22/10/2009 [ 48 ] X-ray crystallography non-systematic errors small problems: ( and look the same) few huge problems newer structures are better proteins are not static overall motion local motion C α C β C α C β C C

49 MR structures different philosophy to X-ray lots of little internal distances do not quite define structure generate 50 or 10 2 solutions look at scatter of solutions as with X-ray some parts are well defined some not structure 1sm7 22/10/2009 [ 49 ]

50 Summarise and stop 22/10/2009 [ 50 ] roles of proteins heteropolymers 20 types of amino acid / residue geometry avoiding atomic clashes, forming H bonds leads to regular secondary structure chemistry of amino acids very different to another unique structure for a sequence reflects these differences representations of structures structures in PDB are experimental have errors