3d structure visualizing, comparing, classifying david wishart athabasca 3-41...
TRANSCRIPT
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Outline & Objectives*
• Visualization Programs
• Vectors & Matrices
• Difference Distance Matrices
• Molecular Superposition
• Measuring Superposition
• Classifying 3D Structures
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PDB Viewers
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Jmol*• Java-based program• Open source applet and application
– Compatible with Linux, MacOS, Windows
• Menus access by clicking on Jmol icon on lower right corner of applet
• Works with all major web browsers – Internet Explorer (Win32) – Mozilla/Firefox (Win32, OSX, *nix) – Safari (Mac OS X) and Opera 7.5.4
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WebMol*
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WebMol*• Both a Java Applet and a downloadable
application• Offers many tools including distance, angle,
dihedral angle measurements, detection of steric conflicts, interactive Ramachandran plot, diff. distance plot
• Compatible with most Java (1.3+) enabled browsers including:– Internet Explorer– Safari on Mac OS– Mozilla 1.6/Firefox on Linux (Redhat 8.0)
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PDB SimpleViewer
Requires Java WebStart (~30 sec install)
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Chime*
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Chime*• http://www.umass.edu/microbio/chime/
neccsoft.htm#download_install
• Among first PDB viewing programs with limited manipulation capacity
• Uses Rasmol for its back end source• View both large and small molecules• Browser Plug-in (Like PDF reader)• Interesting from historical perspective
(now mostly phased out)
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Protein Explorer (Chime)
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Protein Explorer*
• http://www.umass.edu/microbio/chime/pe_beta/pe/protexpl/
• Uses Chime or Jmol for its back-end• Very flexible, user friendly, well documented,
offers morphing, sequence structure interface, comparisons, context-dependent help, smart zooming, off-line
• Browser Plug-in (Like PDF reader)• Compatible with Netscape (Mac & Win)
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QuickPDB
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Quick PDB*
• http://www.sdsc.edu/pb/Software.html
• Very simple viewing program with limited manipulation and very limited rendering capacity -- Very fast
• Java Applet (Source code available)
• Compatible with most browsers and computer platforms
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Rasmol
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Rasmol*
• http://www.umass.edu/microbio/rasmol/
• Very simple viewing program with limited manipulation capacity, easy to use!
• “Grand-daddy” of all visual freeware
• Runs as installed “stand-alone” program
• Source code available
• Runs on Mac, Windows, Linux, SGI and most other UNIX platforms
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B (Biomer)
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Biomer (B)• http://casegroup.rutgers.edu/Biomer/index.html
• Very sophisticated molecular rendering and modelling package for both large and small molecules (kind of rough)
• Supports molecular dynamics & En. min• Written in Java (source code available)• Can run as an applet or stand-alone• Compatible on most platforms
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Swiss PDB Viewer
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Swiss PDB Viewer*
• http://spdbv.vital-it.ch/• Among most sophisticated molecular
rendering, manipulation and modelling packages (commercial or freeware)
• Supports threading, hom. modelling, energy minimization, seq/struc interface
• Stand-alone version only• Compatible on Mac, Win, Linux, SGI
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Swiss PDB Tutorial*
http://spdbv.vital-it.ch/TheMolecularLevel/SPVTut/index.html
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MolMol
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MolMol*
• http://www.mol.biol.ethz.ch/wuthrich/software/molmol/
• Very sophisticated molecular rendering, and manipulation package (among the best graphics of all freeware)
• Special focus on NMR compatibility, supports many calculations/plots
• Stand-alone version only
• Compatible on Win, Unix (nearly all)
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Summary*
Rasmol + + + ++ - - - -
Chime + + - + - - - -
Prot. Expl. + + - ++ + + - -
Quick PDB + + + + + - - -
Biomer + + + ++ - + + +
SwP Viewer + + + +++ + + + +
MolMol - + + +++ - + - +
Mac Win Unix Rendr SeqView Super E Min Modeling
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Visualization Hub
http://www.umass.edu/microbio/chime/top5.htm
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Graphics Formats
• GIF• JPEG• PNG• TIFF (Tag Image)• BMP• EPS• PS• RGP (SGI)
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Graphics Formats*• GIF (Graphical Interchange Format)
– pronounced “JIF”– introduced in 1987 by CompuServe– handles 8 bit colour (256 colours)– lossy compression (up to 10 X)– best for drawings, simple B+W or colour
diagrams, images with hard edges– supported by Perl graphics library (GD.pm)– supports animation & transparency
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Graphics Formats*
• JPEG (Joint Photographic Experts Group)
– pronounced “JAY-peg”– exploits eye’s poor perception of small
changes in colour variation– handles 24 bit colour (1.6 million colours)– allows adjustable lossy compression – best for colour pictures of real objects with
varied colour, shadow, fuzzy edges– among most common web image formats
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Graphics Formats*
• PNG (Portable Network Graphics)
– designed to replace GIF and TIFF– supports lossless compression– supports 24 bit, grayscale and 8 bit – supports transparency & interlacing – offers better compression than GIF (15%)– supported by new GD.pm Perl library– problems with many early browsers in
viewing PNG (now fixed)
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PovRay (www.povray.org)
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Aliasing & Antialiasing*
True Image Aliased Image Anti-aliased Image
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Ray Casting (from 3D to 2D)*• Ray = beam of light• For each pixel on screen,
cast ray from eye thru pixel
• Test every object in scene to see if ray intersects object
• Each ray intersection nearest to eye is made visible, color pixel
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Ray Tracing & Reflection*
• Used to determine surface appearance
• Begins with ray casting, determine intersects, then recursively sends 2ndary rays to see which objects reflect, which are transparent, which absorb, etc.
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Shadowing*
• Uses ray tracing algorithm
• Sends out 2ndary rays towards light sources to see if opaque objects are in the way, if so, then surface is in shadow
• “shadow feelers”
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HAV-3C Protease - Alan Gibbs
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Outline
• Visualization Programs
• Vectors & Matrices
• Difference Distance Matrices
• Molecular Superposition
• Measuring Superposition
• Classifying 3D Structures
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Vectors Define Bonds and Atomic Positions
x
y
z H3N+
O
O
RH
Origin
CO bond
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Review – Vectors*
(1,2,1)
(0,0,0)
u
u = 1i + 2j + 1k^ ^ ^
u =
121
= (1-0)2 + (2-0)2 + (1-0)2 = 6u
Vectors have a length & a direction
x
y
z
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Review - Vectors
• Vectors can be added together
• Vectors can be subtracted
• Vectors can be multiplied (dot or cross or by a matrix)
• Vectors can be transformed (resized)
• Vectors can be translated
• Vectors can be rotated
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Matrices*
• A matrix is a table or “array” of characters • A matrix is also called a tensor of “rank 2”
2 4 6 8 9 41 3 5 7 9 31 0 1 0 1 09 4 6 4 3 53 4 3 4 3 4
row
colu
mn
A 5 x 6 Matrix
# co
lum
ns
# ro
ws
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Different Types of Matrices
2 4 6 8 9 41 3 5 7 9 31 0 1 0 1 09 4 6 4 3 53 4 3 4 3 43 6 7 9 1 0
2 4 6 8 9 44 3 5 7 9 36 5 1 0 1 08 7 0 4 3 59 9 1 3 3 44 3 0 5 4 0
135973
A squareMatrix
A symmetricMatrix
A columnMatrix
(A vector)
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Different Types of Matrices*
A B C D E FG H I J K LM N O P Q RS T U V W X
cos sin 0 sin -cos 0
0 0 1
A rectangularMatrix
A rotationMatrix
A rowMatrix
(A vector)
2 4 6 8 9
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Review - Matrix Multiplication
2 4 01 3 11 0 0
1 0 22 1 30 1 0
2x1 + 4x2 + 0x02x0 + 4x1 + 0x12x2 + 4x3 + 0x01x1 + 3x2 + 1x01x0 + 3x1 + 1x11x2 + 3x3 + 1x01x1 + 0x2 + 0x01x0 + 0x1 + 0x11x2 + 0x3 + 0x0
x10 4 16 7 4 11 1 0 0
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Rotation*
1 0 0 0 cos sin 0 -sin cos
cos sin 0-sin cos 0 0 0 1
Rotateabout x
Rotateabout z
x
z
y
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Rotation*
1 0 0 0 cos sin 0 -sin cos
cos sin 0-sin cos 0 0 0 1
Clockwise about x Clockwise about z
1 0 0 0 cos -sin 0 sin cos
cos -sin 0 sin cos 0 0 0 1
Counterclockwise about x Counterclockwise about z
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Rotation
X =
X =
x
y
z
x
y
z
1 0 0 0 cos sin 0 -sin cos
1 0 0 0 cos sin 0 -sin cos
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Rotation (Detail)*
X =
x
y
z
x
y
z
= cossin-sin + cos
111
1 0 0 0 cos sin 0 -sin cos
1 0 0 0 cos sin 0 -sin cos
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Comparing 3D Structures
• Visual or qualitative comparison
• Difference Distance Matrices
• Superimposition or superposition
• Root mean square deviation (RMSD)
• Subgraph isomorphisms (Ullman’s algorithm)
• Combinatorial extension (CE)
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Qualitative Comparison
Same or Different?
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Outline
• Visualization Programs
• Vectors & Matrices
• Difference Distance Matrices
• Molecular Superposition
• Measuring Superposition
• Classifying 3D Structures
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Difference Distance Matrix*
Object A Object B
AB
C
D
E
A
B
E
D
C
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Difference Distance Matrix*
A B C D EA 0 4 5 6 4B 0 4 6 7C 0 3 6D 0 3E 0
A B C D EA 0 4 5 6 4B 0 4 5 3C 0 3 5D 0 3E 0
A B C D EA 0 0 0 0 0B 0 0 1 4C 0 0 1D 0 0E 0
AB
C
D
E
AB
E
D
C
Hinge motion
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Difference Distance Matrix
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Difference Distance Matrices or DDM’s*
• Simplest method to perform structural comparisons
• Requires no transfomations, no rotations or superpositions
• Very effective at identifying “hinge” motions or localized changes
• Produces a visually pleasing, quantitative measure of similarity
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Superposition*
• Objective is to match or overlay 2 or more similar objects
• Requires use of translation and rotation operators (matrices/vectors)
• Recall that very three dimensional object can be represented by a plane defined by 3 points
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Superposition*
x
y
z
a
b
c
a’
b’
c’
x
y
z
a
b
c
a’
b’
c’
Identify 3 “equivalence” points in objects to be aligned
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b’
c’
Superposition
x
y
z
x
y
z
a
b
c
a’
b’
c’
a
b
c
Translate points a,b,c and a’,b’,c’ to origin
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b’
c’
Superposition
x
y
z
a
b
c b’
c’
x
y
z
a
b
c
Rotate the a,b,c plane clockwise by about x axis
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Superposition
b’
c’
x
y
z
a
b
c
b’
c’
x
y
z
a
bc
Rotate the a,b,c plane clockwise by about z axis
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Superposition
b’
c’
x
y
z
a
bc
b’
c’
x
y
z
a
bc
Rotate the a,b,c plane clockwise by about x axis
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Superposition
b’
c’
x
y
z
a
bc
b’
c’
x
y
z
a
bc
’
Rotate the a’,b’,c’ plane anticlockwise by ’ about x axis
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Superposition
b’
c’
x
y
z
a
bc
b’c’
x
y
z
a
bc
‘
Rotate the a’,b’,c’ plane anticlockwise by ’ about z axis
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Superposition
b’c’
x
y
z
a
bc
Rotate the a’,b’,c’ plane clockwise by ’ about x axis
b’c’
x
y
z
a
bc
’
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Superposition
Apply all rotations and translations to remaining points
b’c’
x
y
z
a
bcb’c’
x
y
z
a
bc
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Superposition
Before After
b’c’
x
y
z
a
bcx
y
z
a
b
c
a’
b’
c’
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Returning to the “red” frame
Before After
y
z
x
b’c’
x
y
z
a
bc
a
b
c
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Returning to the “red” frame*
• Begin with the superimposed structures on the x-y plane
• Apply counterclockwise rot. By • Apply counterclockwise rot. By • Apply counterclockwise rot. By • Apply red translation to red origin
Just do things in reverse order!
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Shortcomings*
• Requires some initial assumptions regarding the anchoring points for superposition
• Anchoring points can’t always a priori be known or easily calculated
• It “privileges” the first point “a” over “c” which is in turn privileged over “b”
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More General Approaches*
• Monte Carlo or Genetic Algorithms
• Matrix methods using least squares or conjugate gradient minimization (McLachlan/Kabsch)
• Lagrangian multipliers
• Rotation Angle Methods
• Quaternion-based methods (fastest)
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Superposition – Applications*
• Ideal for comparing or overlaying two or more protein structures
• Allows identification of structural homologues (CATH and SCOP)
• Allows loops to be inserted or replaced from loop libraries (comparative modelling)
• Allows side chains to be replaced or inserted with relative ease
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Outline
• Visualization Programs
• Vectors & Matrices
• Difference Distance Matrices
• Molecular Superposition
• Measuring Superposition
• Classifying 3D Structures
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Molecule aMolecule b
Measuring Superpositions
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RMSD - Root Mean Square Deviation*
• Method to quantify structural similarity -same as standard deviation
• Requires 2 superimposed structures (designated here as “a” & “b”)
• N = number of atoms being compared
RMSD = (xai - xbi)2+(yai - ybi)2+(zai - zbi)2i
N
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Superpositions for Multiple Structures
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RMSD - For Multiple Structures*
• Requires multiple superimposed structures over a single “averaged” structure (x,y,z)
• N = number of atoms being compared
• M = number of structures superimposed
RMSD = (xai - xi)2+(yai - yi)2+(zai - zi)2i
Na
M
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RMSD without Superposition*
A B C D EA 0 4 5 6 4B 0 4 6 7C 0 3 6D 0 3E 0
A B C D EA 0 4 5 6 4B 0 4 5 3C 0 3 5D 0 3E 0
A B C D EA 0 0 0 0 0B 0 0 1 4C 0 0 1D 0 0E 0
AB
C
D
E
AB
E
D
C RMS = 1+4+1 = 1.8910
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RMSD*
• 0.0-0.5 Å
• <1.5 Å
• < 5.0 Å
• 5.0-7.0 Å
• > 7.0 Å
• > 12.0 Å
• Essentially Identical
• Very good fit
• Moderately good fit
• Structurally related
• Dubious relationship
• Completely unrelated
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SuperPose Web Server
http://wishart.biology.ualberta.ca/SuperPose/
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Outline
• Visualization Programs
• Vectors & Matrices
• Difference Distance Matrices
• Molecular Superposition
• Measuring Superposition
• Classifying 3D Structures
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Classifying Protein Folds*
Lactate Dehydrogenase: Mixed /
Immunoglobulin Fold:
Hemoglobin B Chain:
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Detecting Unusual Relationships
Similarity between Calmodulin and Acetylcholinesterase
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Classifying Protein Folds
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SCOP Database
http://scop.mrc-lmb.cam.ac.uk/scop
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SCOP• Class folding class derived from secondary
structure content
• Fold derived from topological connection, orientation, arrangement and # 2o structures
• Superfamily clusters of low sequence ID but related structures & functions
• Family clusers of proteins with seq ID > 30% with v. similar struct. & function
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SCOP Structural Classification
The eight most frequent SCOP superfolds
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The CATH Database
http://www.cathdb.info
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CATH
• Class [C] derived from secondary structure content (automatic)
• Architecture (A) derived from orientation of 2o structures (manual)
• Topology (T) derived from topological connection and # 2o structures
• Homologous Superfamily (H) clusters of similar structures & functions
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Class 1: Mainly Alpha
CATH - Class
Class 2: Mainly Beta
Class 3: Mixed
Alpha/Beta
Class 4: Few Secondary
Structures
Secondary structure content (automatic)
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Roll
CATH - Architecture
Super Roll Barrel 2-Layer Sandwich
Orientation of secondary structures (manual)
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L-fucose Isomerase
CATH - Topology
Serine Protease Aconitase, domain 4
TIM Barrel
Topological connection and number of secondary structures
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Alanine racemase
CATH - Homology
Dihydropteroate (DHP)
synthetase
FMN dependent fluorescent
proteins
7-stranded glycosidases
Superfamily clusters of similar structures & functions
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Other Servers/Databases
• Dali - http://ekhidna.biocenter.helsinki.fi/dali_server/
• VAST - http://www.ncbi.nlm.nih.gov/Structure/VAST/vast.shtml
• Matras - http://biunit.aist-nara.ac.jp/matras/
• CE - http://cl.sdsc.edu/ce.html
• TopMatch - http://topmatch.services.came.sbg.ac.at/
• PDBsum - http://www.ebi.ac.uk/thornton-srv/databases/pdbsum/
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CE Search
http://cl.sdsc.edu/ce/all-to-all/1-to-all.html
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CE Search
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Summary
• Many different tools and formats to visualize 3D structure – learn how to use at least one of them
• Visualization on computers is mostly about matrix and vector manipulation
• Structure comparison also requires the use of linear algebra
• Protein structures can be compared and aligned – just like sequences