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Chlamydia basic research society.

Report of the 1st biennial conference, Memphis 2003 (continued).

In the session on chlamydial protein secretion, notably type iii (tts) secretion, S. Ouellette (Tennessee) pointed out that in Yersinia low calcium levels play a crucial regulatory role via the low calcium response genes such as LcrH, which may function as a chaperone for the tts components YopD and YopB. In C. pneumoniae LcrH1 and LcrH2 are different in size to Yersinia and are not paralogues of each other. LcrH1 starts at high level in the chlamydial growth cycle, decreasing by 24 hours post infection whereas LcrH2 peaks at mid cycle. LcrH knockouts in Yersinia secrete Yop effectors in the absence of glutamate. The LcrH proteins have tetrapeptide protein - protein interaction domains; the proteins to which they bind are being sought. 

Patrik Bavoil reported that CopN, an analogue of Yersinia YopN and expressed late in the developmental cycle, is secreted and translocated to the inclusion membrane in an RB:membrane contact -dependent manner. Although it should be remembered that the tts system has not been localised to the chlamydial EB or RB projections [where chlamydiologists expect it to be], studies by Akira Matsumoto indicate that CopN is translocated to protrusions on the inner face of the inclusion membrane. Patrik suggested that early after infection, as EB differentiate to RB, they come into contact with the inclusion membrane, thereby stimulating tts secretion. As they divide further the RB lose contact with the membrane, diminishing tts activity. CopN left on broken membrane projections might provoke a break in the chlamydial tts injectisome. Ken Fields in Hackstadt's  laboratory searched for structural components of the tts system by MALDI time of flight spectroscopy in EB lysates, identifying over half of the tts structural components in EBs. One of these, CdsJ, was even present on EBs whose protein synthesis had been blocked with chloramphenicol. Secretion of inclusion membrane proteins by RBs was, however, blocked by chloramphenicol. It was suggested that there is a tts injectisome primed and "ready to go" that is   present in EBs at the beginning of the developmental cycle.

Another important chlamydial protein, CPAF, is involved in the proteolytic degradation of host cell transcription factors involved in the regulation of histocompatability antigen expression [see: antigen processing]. Feng Dong (Texas) reported that CPAF degrades keratin 8, a component, with keratin 18, of the intermediate filaments characteristic of epithelial cells. 

In the session on persistent chlamydial infection / heat shock proteins, Bob Belland pointed out that there are interstrain intraspecific polymorphisms in the tyrP gene. Thus in the C. pneumoniae CWL 029 genomic sequence the tyrP gene occurs as a tandem duplication; in the Japanese C. pneumoniae J138 sequence it occurs as a single gene; whereas in the C. pneumoniae AR39 sequence it occurs as both a single gene and as tandem repeats. TyrP encodes a permease transporting tyrosine and tryptophan, crucial in C. pneumoniae which has no genes for tryptophan biosynthesis. Cardiovascular & peripheral blood isolates of C. pneumoniae tended to have single gene copies of tyrP whereas respiratory strains had up to three copies of tyrP. [It remains to be seen if this will hold true over larger numbers of isolates]. Duplication of tyrP appeared to be an old event, may confer survival advantages for C. pneumoniae adapting to low tryptophan levels, and it is speculated may  lead to a greater likelihood of persistent infection. Triple tyrP strains took up aromatic amino acid to a much greater extent than single copy strains. 

Alan Hudson (Wayne State) pointed out that both C. trachomatis and C. pneumoniae have multiple hsp60 encoding proteins in the GroEL-ES operon, as do the facultatively intracellular bacteria, Mycobacterium tuberculosis and M. leprae. In active infection of Hep-2 cells, all three C. trachomatis gro-EL genes [CT604, 110 & 755] were expressed at differing times in the developmental cycle. In a model of persistent infection of C. trachomatis serovar K in monocytes, only CT604 was significantly expressed. Large amounts of CT 604 transcripts were also found in synovial tissue from a limited number of reactive arthritis patients. This indicated that in C. pneumoniae and C. trachomatis the three hsp genes are expressed independently of each other and may have different biological roles. Karuna Karunakaran in an elegant paper [see: Karunakaran et al., 2003; Memphis presentation] mapped these GroEL-ES homologues onto the comparable E. coli structure. The GroEL-ES chaperonin consists of 14 subunits of GroEL on the top of which is an apical domain binding to GroES and also capable of polypeptide binding. At the bottom is a region for ATP binding. In the GroEL1, 2 and 3 there are significant differences in amino acid composition in the ATP binding region, probably leading to differences in their ability to chaperone specific damaged proteins. These genes had different phylogenetic lineages and only GroEL1, GroES and dnaK were elevated during heat shock. GroEL2 also occasionally uses rare nucleotide codons for arginine and for isoleucine, which may be significant for regulating the translation of message derived from these genes.

I did not attend  the host chlamydia interactions session so if anybody else would like to fill in the gaps, please contact the writer using the email links on the bottom border.

[MEW] March 18th, 2003

NEXT: Memphis 3 continued

References

Karunakaran, K. P., Noguchi, Y., Read, T. D., Cherkasov, A., Kwee, J., Shen, C., Nelson, C. C. & Brunham, R. C. (2003). Molecular analysis of the multiple GroEL proteins of Chlamydiae. Journal of Bacteriology 185, 1958 - 1966.