Localization and characterization of two putative TMH family proteins in Chlamydia psittaci

Abstract

Chlamydia psittaci (C. psittaci), an obligate intracellular agent of psittacosis, causes an atypical pneumonia in humans. The transmembrane head proteins (TMH) of C. psittaci, putatively belong to the Inc family and presumably play similar roles. CPSIT_0844 and CPSIT_0846 were the putative TMH proteins of C. psittaci. To identify these two proteins, antisera were raised with fusion proteins which were prokaryotic expressed in Escherichia coli and purified. By immunofluorescence assay, CPSIT_0844 and CPSIT_0846 were localized in the inclusion membrane of C. psittaci-infected cells. By RT-PCR and western blot analysis to detect the temporal expression, CPSIT_0844 and CPSIT_0846 were detected as early as 12h post-infection (p.i.) and 6h p.i., separately; meanwhile, in secretions monitored with immunofluorescence assay, these proteins were observed in the inclusion membrane at 18h p.i. and remained in the inclusion membrane throughout the growth cycle. CPSIT_0844 and CPSIT_0846 could specifically be recognized by the antiserum of C. psittaci but failed to react with the antiserums of Chlamydia trachomatis and Chlamydia pneumoniae, which is consistent with the fact that they had no significant orthologs in C. trachomatis and C. pneumoniae. These results revealed that CPSIT_0844 and CPSIT_0846, the putative TMH family proteins, might be unique to C. psittaci and could be used to diagnose the infection caused by C. psittaci. Moreover, CPSIT_0844 and CPSIT_0846 could induce the expression of the inflammatory cytokines IL-1β, IL-6 and TNF-α in THP-1 cells, which might contribute to chlamydia-induced inflammatory pathologies.

The cellular ceramide transport protein CERT promotesChlamydia psittaciinfection and controls bacterial sphingolipid uptake

“…Eight tmh genes are found in the C. psittaci genome, and two of them have been shown experimentally to localise to the inclusion membrane later than 18‐hr p.i. (Voigt et al, ; Wu et al, ). Whether TMH or Inc proteins are involved in recruiting CERT to the C. psittaci inclusions remains to be determined.…”

Transcription of seven genes in a model of interferon-γ-induced persistent Chlamydia psittaci infection

“…CPSIT-0594 encodes protein IncA. CPSIT-0846 and CPSIT-0844 are two putative transmembrane head protein family proteins which are additionally located in the inclusion membrane, and have been predicted to be type III secretion system (T3SS) effector protein encoding genes (44). Inc proteins may be associated with the processes of inclusion formation, transportation to the nuclear space and evasion of early lysosomal fusion (45,46).…”

The Hypothetical Inclusion Membrane Protein CPSIT_0846 Regulates Mitochondrial-Mediated Host Cell Apoptosis via the ERK/JNK Signaling Pathway

“…CPSIT_0846 is also a member of the transmembrane head (TMH) protein family, which shares 84% homology with the TMH family protein secreted by C. abortus. We previously found that CPSIT_0846 not only promoted the production of tumor necrosis factor alpha (TNF-a), interleukin (IL)-1b, and IL-6 in human monocytic THP-1 cells in vitro, but also induced a strong humoral and cellular immune response in mice (Wu et al, 2016;Ran et al, 2017). Therefore, we speculate that this protein may be closely related to the pathogenic mechanism of C. psittaci.…”

“…Moore and his colleagues found Chlamydial IncA interacted with the G3BP1 partner, and affected the expression of c-myc mRNA, thereby inhibiting host cell apoptosis (Moore and Ouellette, 2014). CPSIT_0846, the homolog of C. psittaci IncA, can be detected at 2 h after host cell infection, and throughout the whole development cycle (Wu et al, 2016). So, CPSIT_0846 may also participates in the pathogenesis of C. psittaci by regulating apoptosis in host cells.…”