Statistical analysis results in terms of species and PTM types. (A) Statistical results of the entries (PDB chains) from the eight largest species, including Homo sapiens, Escherichia coli, Saccharomyces cerevisiae, Mus musculus, Mycobacterium tuberculosis, Rattus norvegicus, Bos taurus and Thermus thermophiles; (B) Statistical analysis of the PTM sites from the eight largest species; (C) Distributions of eight largest PTM types in terms of the number of PTM entries; and (D) Distributions of eight largest PTM types in terms of the number of PTM sites.