Mass Spectrometry

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Mass Spectrometry Protein Sequencing

• Micro 343
• David Wishart Rm. Ath 3-41
• david.wishart_at_ualberta.ca

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Objectives

• Learn about the principles and applications of
  tandem mass spectrometry especially in the area
  of protein and peptide sequencing
• To learn about new MS approaches to identifying
  or sequencing large numbers of proteins
• Applications of MS to Proteomics

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Different Types of MS

• GC-MS - Gas Chromatography MS
• separates volatile compounds in gas column and
  IDs by mass
• LC-MS - Liquid Chromatography MS
• separates delicate compounds in HPLC column and
  IDs by mass
• MS-MS - Tandem Mass Spectrometry
• separates compound fragments by magnetic field
  and IDs by mass

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Tandem Mass Spectrometer
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Tandem Mass Spectrometry

• Purpose is to fragment ions from parent ion to
  provide structural information about a molecule
• Also allows separation and identification of
  compounds in complex mixtures
• Uses two or more mass analyzers/filters separated
  by a collision cell filled with Argon or Xenon
• Collision cell is where selected ions are sent
  for further fragmentation

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Tandem Mass Spectrometry

• Different MS-MS configurations
• Quadrupole-quadrupole (low energy)
• Magnetic sector-quadrupole (high)
• Quadrupole-time-of-flight (low energy)
• Time-of-flight-time-of-flight (low energy)
• Fragmentation experiments may also be performed
  on single analyzer instruments such as ion trap
  instruments and TOF instruments equipped with
  post-source decay

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MS-MS Proteomics
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MS-MS Methods

• 2D-GE MALDI-MS
• Peptide Mass Fingerprinting (PMF)
• 2D-GE MS-MS
• Sequence Tag/Fragment Ion Searching
• Multidimensional LC MS-MS
• ICAT Methods (isotope labelling)
• MudPIT methods
• 1D-GE LC MS-MS
• De Novo Peptide Sequencing (MS-MS)

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2D-GE MS-MS
Trypsin Gel punch
p53
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MudPIT
IEX-HPLC
RP-HPLC
Trypsin proteins
p53
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ICAT (Isotope Coded Affinity Tag)
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The ICAT Reagent
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ICAT Quantitation
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MS-MS for Protein ID

• Proteins are isolated (from gel or HPLC) and
  subjected to tryptic digestion
• Peptides are sent through ionizer and into a
  collision cell where the doubly charged ions are
  selected and fragmented through collision induced
  decay (CID)
• The resulting singly charged ions (daughter ions)
  are analyzed to determine the sequence or to ID
  the parent peptide

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Why Trypsin for MS-MS?

• CID of peptides less than 2-3 kD is most reliable
  for MS-MS studies The frequency of tryptic
  cleavage guarantees that most peptides will be of
  this size
• Trypsin cleaves on the C-terminal side of
  arginine and lysine. By putting the basic
  residues at the C-terminus, peptides fragment in
  a more predictable manner throughout the length
  of the peptide

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Why Double Charges?

• Easiest spectra to interpret are those obtained
  from doubly-charged peptide precursors, where the
  resulting fragment ions are mostly singly-charged
  
• Doubly-charged precursors also fragment such that
  most of the peptide bonds break with comparable
  frequency, such that one is more likely to derive
  a complete sequence

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MS-MS Peptide Fragments

• When peptides are proteins are admitted to a
  collision cell the peptide usually fragments at
  the weakest bond (the peptide bond, but some
  CH-NH and CH-CO breakage also occurs)
• Collision conditions have to be optimized for
  each peptide
• Two main types of daughter ions are produced --
  b ions and y ions

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MS-MS Peptide Fragmentation
yn-1
yn-2
y1
R1
R2
R3
Rn
H2N-CH-CO-NH-CH-CO-NH-CH-COCO-NH-CH-CO2H
b1
b2
bn-1
b1 y1 b2 y2 b3 y3 b4 y4 b5
y5
signal
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MS-MS Peptide Fragmentation
Ala-Gly-His-Leu-.Phe-Glu-Cys-Tyr
b1 y1 b2 y2 b3 y3 b4 y4 b5
y5
signal
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Tandem MS of BSA
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MS-MS of Fibrinogen
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Amino Acid Residue Masses
Monoisotopic Mass
Glycine 57.02147 Alanine 71.03712 Serine 87.03203
Proline 97.05277 Valine 99.06842 Threonine 101.04
768 Cysteine 103.00919 Isoleucine 113.08407 Leucin
e 113.08407 Asparagine 114.04293
Aspartic acid 115.02695 Glutamine 128.05858 Lysin
e 128.09497 Glutamic acid 129.04264 Methionine 1
31.04049 Histidine 137.05891 Phenylalanine 147.06
842 Arginine 156.10112 Tyrosine 163.06333 Trypto
phan 186.07932
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MS/MS The Movie (Kathleen Binns)

• http//www.mshri.on.ca/pawson/ms/movie.html

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Protein ID by MS-MS

• Peptide fragments from target protein are
  sequenced by MS-MS using a variety of algorithms
  (SEQUEST, Mascot) or via manual methods
• The peptide fragment sequences are sent to BLAST
  to be queried against a protein sequence database
• The protein having the highest number of sequence
  matches is IDd as the target

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SEQUEST

• Algorithm developed for MS-MS fragment ion
  identification by J. Eng (1994) in John Yates Lab
  (Scripps, U Wash)
• Compares predicted MS-MS spectra against observed
  daughter ion spectra to identify and rank matches
  (no sequencing per se)

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SEQUEST and 2D-GE
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SEQUEST Algorithm

• SEQUEST correlates uninterpreted tandem mass
  (MS-MS) spectra of peptides with amino acid
  sequences from protein and nucleotide databases
• SEQUEST will determine the amino acid sequence
  and thus the protein(s) and organism(s) that
  correspond to the mass spectrum being analyzed
• SEQUEST is distributed by Finnigan Corp.

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SEQUEST Algorithm
Sequence DB Calc. Tryptic Frags Calc. MS-MS
Spec.
gtP12345 acedfhsakdfqea sdfpkivtmeeewe ndadnfekgpfn
a gtP21234 acekdfhsadfqea sdfpkivtmeeewe nkdadnfeq
wfe gtP89212 acedfhsadfqeka sdfpkivtmeeewe ndakdnf
eqwfe
acedfhsak dfgeasdfpk ivtmeeewendadnfek gpfna
acek dfhsadfgeasdfpk ivtmeeewenk dadnfeqwfe ace
dfhsadfgek asdfpk ivtmeeewendak dnfegwfe
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Creating a Synthetic MS-MS Spectrum for GPFNA
b ions y ions
G 57
P 97
F 147
N 114
A 71
A 71
N 114
F 147
P 97
G 57
57 154 301 415 486
71 185 332 429 486
combine
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SEQUEST Algorithm
Query Spectrum Spectral Database Result
acedfhsak
mtlsyk
giqwemncyk
nmqtydr
Score 128 Accession P12345 Protein p53 Org.
Homo sapiens
giqwemncyk
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Alternatives to SEQUEST

• Web software and servers using algorithms based
  on manual methods
• Sending your data to friends who have a SEQUEST
  license
• Manual analysis of MS-MS spectra
• This is still the most reliable method for
  interpreting MS-MS spectra
• Also allows for de-novo sequencing

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MS-MS on the Web

• PepSea (disabled)
• http//195.41.108.38/PA_SequenceOnlyForm.html
• ProteinProspector
• http//prospector.ucsf.edu/
• PeptideSearch (limited)
• http//www.narrador.embl-heidelberg.de/GroupPages/
  Homepage.html
• Mascot (probably the best)
• www.matrixscience.com

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Mascot MS-MS Form
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Mascot MS-MS Input Format
COM10 pmol digest of Sample X15 ITOL1
ITOLUDa MODSMet Ox,Cys B propionamide
MASSMonoisotopic USERNAMELou Scene
USEREMAILleu_at_altered-state.edu CHARGE2 and
3 BEGIN IONS TITLEPeak 1 PEPMASS983.6
846.60 73 846.80 44 847.60 67
Parent ion Mass (2)
Daughter ion mass
intensity
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Mascot MS-MS Output
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Mascot MS-MS Output
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A Real Example
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Protocols for MS-MS Sequencing

• Usually cant tell a b ion from a y ion
• Assume the lowest mass visible in the spectrum is
  a lysine or arginine (this is the y1 ion) this is
  because trypsin cuts after a lysine or arginine
• This y1 mass should be 147.113 for lysine or
  175.119 for arginine The y1 ion is calculated by
  adding 19.018 u (three hydrogens and one oxygen)
  to the residue masses of lysine and arginine

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MS-MS Sequencing

• Using the mass tables, look to the right of y1
  and see if you can find another prominent peak
  that is equal to y1 AA where AA is the residue
  mass for any of the 20 amino acids. This is the
  y2 ion
• Proceed in a rightward direction, identifying
  other yn ions that differ by an AA residue mass
  (dont expect to find all)
• The yn series produces a reverse sequence
• Watch for possible dipeptide peaks that may fool
  you

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Amino Acid Residue Masses
Monoisotopic Mass
Glycine 57.02147 Alanine 71.03712 Serine 87.03203
Proline 97.05277 Valine 99.06842 Threonine 101.04
768 Cysteine 103.00919 Isoleucine 113.08407 Leucin
e 113.08407 Asparagine 114.04293
Aspartic acid 115.02695 Glutamine 128.05858 Lysin
e 128.09497 Glutamic acid 129.04264 Methionine 1
31.04049 Histidine 137.05891 Phenylalanine 147.06
842 Arginine 156.10112 Tyrosine 163.06333 Trypto
phan 186.07932
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Things To Remember

• Gly Gly 114.043 u and Asn 114.043 u
• Ala Gly 128.059 u and Gln 128.059 u and Lys
  128.095 u
• Gly Val 156.090 u and Arg 156.101 u
• Ala Asp Glu Gly 186.064 and Trp 186.079
  u
• Ser Val 186.100 u and Trp 186.079 u
• Leu Ile 113.084u

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MS-MS Sequencing

• Use the remaining unassigned peaks to see if
  you can construct a b ion series
• The highest mass peak corresponds to the parent
  ion or parent minus 147 (K) or 175 (R)
• The b ions give the normal sequence
• Both forward (b ion) and backward (y ion)
  sequences should be consistent
• Use the resulting sequence tag to search the
  databases using BLAST (remember to use a high
  Expect value 100) to see if the sequence
  matches something

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Tandem MS of BSA
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Different MS-MS Instruments Yield Different
Spectra

• A typical QTOF or triple quad MS-MS spectrum of a
  tryptic peptide contains a continuous series of
  y-type ions. The b-type ions are usually seen
  only at lower masses below the precursor m/z
  value
• Ion trap CID data of tryptic peptides is
  different in that one often finds a continuous
  series of both b-type and y-type ions throughout
  the spectrum

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Post-Translational Modifications (PTM)
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PTM by MALDI (PMF)
Database MKALSPVRGCYEAVCCLSERSLAIARGRGKSPSAEEPLSL
LDDMNHCYSRLRELVPGVPRGTQLSQVEILQRVIDYILDLQVVLAEPAPG
PPDGPHLPIQVREGARPGSSERAGWDAAGLPHRVLEYLG AVAKVELRG
TVQPASNFNDDSSQGLGTDEGSIVLTQRSNAQAVEGAGTDESTLIELMAT
RNNQEIAAINEAYSLEDDLSSDTSGHFRILVSLALGNRDEGPENLTQAVV
AETLNKPAFFADRLLALXGGDD MRWLTPFGMLFISGTYYGLIFFGLIM
EVIHNALISLVLAFFVVFAWDLVLSLIYGLRFVKEGDYIALDWDGQFPDC
YGLFASTCLSAVIWTYTDSLLLGLIVPVIIVFLGKQLMRGLYEKIKS
GTVQPASNFNDDSSQGLGTDEGSIVLTQR
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PTM by MS-MS
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Phosphoserine Detection
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De Novo Sequencing (MS-MS)

• Done when sample is not amenable to Edman
  Degradation
• Done when no sequence or PMF match seems to exist
  in databases
• Requires a very high resolution mass analyzer
  (FT-ICR, QTOF or Qstar instrument) with lt20 ppm
  resolution
• Usually requires multi-enzyme digestion
• Still a difficult process but possible to do at
  much lower amounts than Edman Deg.

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MS-MS Proteomics
Advantages Disadvantages

• Provides precise sequence-specific data
• More informative than PMF methods (gt90)
• Can be used for de-novo sequencing (not entirely
  dependent on databases)
• Can be used to ID post-trans. modifications

• Requires more handling, refinement and sample
  manipulation
• Requires more expensive and complicated equipment
• Requires high level expertise
• Slower, not generally high throughput