Molecular analysis of the multiple GroEL proteins of Chlamydiae

Genome sequencing revealed that all six chlamydiae genomes contain three groEL-like genes (groEL1, groEL2, and groEL3). Phylogenetic analysis of groEL1, groEL2, and groEL3 indicates that these genes are likely to have been present in chlamydiae since the beginning of the lineage. Comparison of deduced amino acid sequences of the three groEL genes with those of other organisms showed high homology only for groEL1, although comparison of critical amino acid residues that are required for polypeptide binding of the Escherichia coli chaperonin GroEL revealed substantial conservation in all three chlamydial GroELs. This was further supported by three-dimensional structural predictions. All three genes are expressed constitutively throughout the developmental cycle of Chlamydia trachomatis, although groEL1 is expressed at much higher levels than are groEL2 and groEL3. Transcription of groEL1, but not groEL2 and groEL3, was elevated when HeLa cells infected with C. trachomatis were subjected to heat shock. Western blot analysis with polyclonal antibodies raised against recombinant GroEL1, GroEL2, and GroEL3 demonstrated the presence of the three proteins in C. trachomatis elementary bodies, with GroEL1 being present in the largest amount. Only C. trachomatis groEL1 and groES together complemented a temperature-sensitive E. coli groEL mutant. Complementation did not occur with groEL2 or groEL3 alone or together with groES. The role for each of the three GroELs in the chlamydial developmental cycle and in disease pathogenesis requires further study.