title: The Shannon information entropy of protein sequences.
abstract: A comprehensive data base is analyzed to determine the Shannon information content of a protein sequence. This information entropy is estimated by three methods: a k-tuplet analysis, a generalized Zipf analysis, and a "Chou-Fasman gambler." The k-tuplet analysis is a "letter" analysis, based on conditional sequence probabilities. The generalized Zipf analysis demonstrates the statistical linguistic qualities of protein sequences and uses the "word" frequency to determine the Shannon entropy. The Zipf analysis and k-tuplet analysis give Shannon entropies of approximately 2.5 bits/amino acid. This entropy is much smaller than the value of 4.18 bits/amino acid obtained from the nonuniform composition of amino acids in proteins. The "Chou-Fasman" gambler is an algorithm based on the Chou-Fasman rules for protein structure. It uses both sequence and secondary structure information to guess at the number of possible amino acids that could appropriately substitute into a sequence. As in the case for the English language, the gambler algorithm gives significantly lower entropies than the k-tuplet analysis. Using these entropies, the number of most probable protein sequences can be calculated. The number of most probable protein sequences is much less than the number of possible sequences but is still much larger than the number of sequences thought to have existed throughout evolution. Implications of these results for mutagenesis experiments are discussed.
authors.affiliation: Department of Chemistry, University of Denver, Colorado 80208, USA.
authors.forename: B J
authors.initials: BJ
authors.lastname: Strait
authors.forename: T G
authors.initials: TG
authors.lastname: Dewey
mesh_terms: D000465:Algorithms; D000595:Amino Acid Sequence; D055592:Biophysical Phenomena; D001703:Biophysics; D019277:Entropy; D019143:Evolution, Molecular; D007257:Information Theory; D008956:Models, Chemical; D016296:Mutagenesis; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry* / Q000235:genetics
chemical_list: D011506:Proteins