Ribosomal protein judgement method, biological species identification method, and mass spectrometry apparatus
Provided is a ribosomal protein judgement method, comprising: an attribution step that involves comparing observed m/z values indicated by peaks on a mass spectrum detected by mass spectrometry of a sample containing ribosomal proteins, with first calculated m/z values based on a database, and attributing at least some of the peaks thus detected to ribosomal proteins; and a presumption step that involves presuming a protein corresponding to a peak with a relative intensity from 50 to 150% relative to an approximate curve or an approximate straight line plotted with relative intensities of the peaks attributed to ribosomal proteins, to be a ribosomal protein.
1 . A ribosomal protein determination method, comprising:
an attribution step of comparing observed m/z values of peaks in a mass spectrum obtained by mass spectrometry of a sample containing ribosomal proteins with first calculated m/z values of ribosomal proteins based on a database, and attributing, among the obtained peaks, one or more peaks having observed m/z values that match the first calculated m/z values as ribosomal proteins peaks;
a step of generating, from m/z values and relative intensities of the peaks attributed as ribosomal protein peaks, an approximate curve or an approximate straight line representing relative intensity as a function of m/z; and
an estimation step of estimating, as a ribosomal protein peak, an unassigned peak that was not attributed as a ribosomal protein peak in the attribution step and that has a relative intensity of 50% to 150% of the relative intensity indicated by the approximate curve or the approximate straight line at the m/z value of the unassigned peak.
2 . The ribosomal protein determination method according to claim 1 , wherein the first calculated m/z values are calculated with consideration of post-translational modification.
3 . The ribosomal protein determination method according to claim 2 , wherein the post-translational modification is N-terminal methionine cleavage.
4 . The ribosomal protein determination method according to claim 1 , wherein the mass spectrometry is matrix-assisted laser desorption/ionization mass spectrometry.
5 . The ribosomal protein determination method according to claim 1 , wherein the sample is of eukaryote origin.
6 . The ribosomal protein determination method according to claim 1 , wherein the sample is a ribosomal protein fraction.
7 . The ribosomal protein determination method according to claim 1 , further comprising:
a verification step of calculating a second calculated m/z value of the protein estimated to be a ribosomal protein, with consideration of post-translational modification, and comparing the second calculated m/z value with the observed m/z values.
8 . The ribosomal protein determination method according to claim 1 , further comprising:
a step of obtaining information from a database about a candidate protein corresponding to the peak estimated in the estimation step to be a ribosomal protein peak;
a step of applying a modification pattern not considered for the first calculated m/z value, to an amino acid sequence of the candidate protein to recalculate a mass and determine a second calculated m/z value; and
a step of, when the second calculated m/z value matches the observed m/z value, attributing the peak as a ribosomal protein peak.
9 . The ribosomal protein determination method according to claim 8 , wherein when the second calculated m/z value matches the observed m/z value, based on the m/z value of the peak attributed as a ribosomal protein peak, a type of a microorganism is identified.
10 . A biological species identification method, wherein ribosomal proteins are determined by the ribosomal protein determination method according to claim 1 , and a species of a living thing that gives amino acid sequence information of the ribosomal proteins is identified.
11 . The biological species identification method according to claim 10 , wherein the living thing is a microorganism.
12 . A mass spectrometry apparatus comprising:
a mass separation member that separates ions based on m/z values;
a detection member that detects the ions separated by the mass separation member;
based on the ions detected by the detection member; and
a determination member that determines, from the mass spectrum, peaks that are attributable as ribosomal protein peaks based on a database, generates, from relative intensities of the peaks attributed as ribosomal protein peaks, an approximate curve or an approximate straight line representing relative intensity as a function of m/z, and selects an unassigned peak that was not attributed as a ribosomal protein peak by the determination member and that has a relative intensity of 50% to 150% of the relative intensity indicated by the approximate curve or the approximate straight line at the m/z value of the unassigned peak.
13 . The mass spectrometry apparatus according to claim 12 , comprising a verification member that attributes the peak thus selected, as a ribosomal protein, with further consideration of post-translational modification.