title: Hydrogen bonding between cytosine and peptides of threonine or serine: is it relevant to the origin of the genetic code?
abstract: 13C, 15N, and 1H nuclear magnetic resonance measurements indicate that chloroform-soluble threonine-containing tripeptide derivatives, such as t-Boc-Thr-Gly-Gly-OBz, form three strong hydrogen bonds to the cytosine moiety of 2',3'-O-isopropylidene-5'-O-t-butyldimethylsilylcytidine. The C = O and NH of the central peptide residue plus the OH of the threonine side chain appear to form bonds to the N(4')H2, N(3), and C(2) = O, respectively, of the pyrimidine. An association constant calculated from the cytidine 15N(4') nuclear magnetic resonance response to added peptide is four times larger than the corresponding cytosine-guanine constant. It is suggested that cytosine-peptide bonding was part of the primitive genetic coding mechanism early in evolution and accounts for the origin of the cytosine-centered codons for the hydroxy amino acids, serine and threonine, in the present code.
mesh_terms: D003062:Codon; D003596:Cytosine; D005815:Genetic Code; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D009690:Nucleic Acid Conformation; D009842:Oligopeptides; D011487:Protein Conformation; D012694:Serine; D013912:Threonine
chemical_list: D003062:Codon; D009842:Oligopeptides; D013912:Threonine; D012694:Serine; D003596:Cytosine