Functional role of a consensus peptide which is common to alpha-, beta-, and gamma-tubulin, to actin and centractin, to phytochrome A, and to the TCP1 alpha chaperonin protein.

The TRiC (TCP1 Ring Complex) chaperonin complex participates in the functional folding of actin, centractin, alpha-, beta-, gamma-tubulin, and phytochrome. Each of the cytoskeletal proteins contain a peptide, RK(A,C,T)F/KRAF, located towards the C-terminus, which is homologous to a TCP1 alpha peptide, while the equivalent phytochrome peptide (RLKAF in certain isoforms) is very similar to the KLRAF peptide of TCP1 alpha. We propose that this TCP1 alpha peptide binds to the nascent polypeptides as they emerge from the ribosome, that this binding restricts the folding pathway, and that the TCP1 alpha peptide is subsequently displaced by the synthesis of the consensus peptide. This hypothesis is strongly supported by the crystallographic structure of actin.