Sequence and structural homology between a mouse T-complex protein TCP-1 and the 'chaperonin' family of bacterial (GroEL, 60-65 kDa heat shock antigen) and eukaryotic proteins.

A mammalian cytoplasmic protein TCP-1, encoded by a gene within the mouse t-complex, has been found to exhibit highly significant (p much less than 0.00001) sequence homology to the 'chaperonin' family of bacterial and eukaryotic proteins (viz. groEL protein of E. coli, rubisco subunit binding protein of plant chloroplasts, yeast hsp58 and mammalian P1 proteins and 60-65 kDa mycobacterial antigen). With the introduction of few gaps, the amino acid sequence of TCP-1 shows between 60-63% similarity (17-20% identical residues and 42-45% conserved substitutions) throughout its length to various chaperonin proteins, indicating a common evolutionary origin. The sequence data also suggest that in contrast to the endosymbiotic origin of mitochondrial and chloroplast chaperonins, the cytoplasmic TCP-1 may have directly descended from the common universal ancestor via eukaryotic lineage. The observed similarity between TCP-1 and the 60-65 kDa bacterial 'common antigen' is also of importance from the viewpoint of immune/autoimmune response.