Characterization of hypothetical proteins Cpn0146, 0147, 0284 &amp; 0285 that are predicted to be in the Chlamydia pneumoniae inclusion membrane

Jianhua Luo,Kaiyang Liu,Youmin Zhong,Guangming Zhong,Tianjun Jia,Guangchao Liu,Ding Chen

doi:10.1186/1471-2180-7-38

Characterization of hypothetical proteins Cpn0146, 0147, 0284 & 0285 that are predicted to be in the Chlamydia pneumoniae inclusion membrane

Jianhua Luo, Kaiyang Liu + Show 5 more

Open Access

https://doi.org/10.1186/1471-2180-7-38

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Abstract

BackgroundAlthough more than 100 Chlamydia pneumoniae hypothetical proteins have been predicted to be inclusion membrane proteins, only a few have been experimentally demonstrated to be in the inclusion membrane. Using antibodies raised with fusion proteins, we characterized four such hypothetical proteins encoded by two gene clusters (Cpn0146-147 and Cpn0284-285) in the C. pneumoniae genome.ResultsCpn0146 and 0147 were detected in the inclusion membrane while Cpn0284 and 0285 inside inclusion and mainly associated with reticulate bodies although all four proteins contain an N-terminal bi-lobed hydrophobic region, a signature motif assigned to inclusion membrane proteins. These four hypothetical proteins were only detected in cells infected with C. pneumoniae but not other chlamydial species, with Cpn0147 at 6 hours and Cpn0146, 0284 & 0285 at 24 hours after infection. Cpn0146 & 147 but not Cpn0284 and 285 co-localized with a host cell endoplasmic reticulum marker, a property known to be possessed by some chlamydial inclusion membrane proteins, when expressed in the host cell cytosol via transgenes. However, the endoplasmic reticulum localization of the C. pneumoniae inclusion membrane proteins did not result in inhibition of the subsequent C. pneumoniae infection.ConclusionThe hypothetical proteins Cpn0146 & 0147 were localized in the C. pneumoniae inclusion membrane while Cpn0284 & 0285 within the inclusion although all four were predicted to be Inc proteins, suggesting the need to experimentally characterize the predicted Inc proteins.

Highlights

More than 100 Chlamydia pneumoniae hypothetical proteins have been predicted to be inclusion membrane proteins, only a few have been experimentally demonstrated to be in the inclusion membrane
The antibodies raised with Cpn0284 and 0285 fusion proteins labeled dominant signals within the inclusions (Fig. 1C), similar but not identical to the signals revealed by the anti-MOMP or anti-HSP60 antibodies
To further exclude the GST tag effect, we evaluated the reactivity between the anti-GST fusion protein antibodies and the Red fluorescence protein (RFP)-C. pneumoniae fusion proteins expressed in transfected cells (Fig. 2B)

Summary

Introduction

More than 100 Chlamydia pneumoniae hypothetical proteins have been predicted to be inclusion membrane proteins, only a few have been experimentally demonstrated to be in the inclusion membrane. The obligate intracellular chlamydial pathogens include the species Chlamydia trachomatis (C. trachomatis; [1]) and C. pneumoniae [2] that mainly infect humans and C. muridarum (formerly known as C. trachomatis mouse pneumonitis agent, designated as MoPn, ref: [2]), C. caviae [3], C. psittaci (38), C. abortus [4] and C. felis [5] that are mainly animal pathogens. The C. psittaci 6BC organisms cause avian chlamydiosis that can lead to serious health problems for humans who are in close contact with the infected birds [12]. Both the C. abortus &C. felis organisms can affect the health of various domesticated animal species [4,13,14]. Despite the profound difference in host range, tissue tropism, disease process, all chlamydial species share similar genome sequences [1,2,3,4,5] and possess a common intracellular growth cycle with distinct biphasic stages [15]

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