The identity of eleven amino acids in the protein chain may define the Cα and Cβ branches of PKA catalytic subunits.

<p>Our full set of PKA catalytic subunits (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060935#pone.0060935.s003" target="_blank">Materials and Methods S1</a>) from bony fishes and tetrapods, comprising 27 Cα and 33 Cβ, was employed to identify eleven amino acid positions that together may be used to classify a PKA catalytic subunit as belonging to one of the two branches. The sequence logos define the PKA Cα and Cβ clades within the <i>Teleostomi</i>, which includes the familiar classes of bony fishes, birds, mammals, reptiles, and amphibians. We find invariable Gln35, Thr37, Glu64, Gly66, His68, Ser109 and Glu334 in Cα and invariable Asp42, Gln67, and Arg319 in Cβ (Cα1/Cβ1 numbering). The residues in the corresponding positions in human Cα1 and Cβ1 are also shown.