Biochemical and Genetic Analysis of the Chlamydia GroEL Chaperonins

Cryo-EM structure and molecular dynamic simulations explain the enhanced stability and ATP activity of the pathological chaperonin mutant

Chaperonins Hsp60s are required for cellular vitality by assisting protein folding in an ATP-dependent mechanism. Although conserved, the human mitochondrial mHsp60 exhibits molecular characteristics distinct from the E. coli GroEL, with different conformational assembly and higher subunit association dynamics, suggesting a different mechanism. We previously found that the pathological mutant mHsp60V72I exhibits enhanced subunit association stability and ATPase activity. To provide structural explanations for the V72I mutational effects, here we determined a cryo-EM structure of mHsp60V72I. Our structural analysis combined with molecular dynamic simulations showed mHsp60V72I with increased inter-subunit interface, binding free energy, and dissociation force, all contributing to its enhanced subunit association stability. The gate to the nucleotide-binding (NB) site in mHsp60V72I mimicked the open conformation in the nucleotide-bound state with an additional open channel leading to the NB site, both promoting the mutant's ATPase activity. Our studies highlight the importance of mHsp60's characteristics in its biological function.

When Bacteria and Viruses Collide: A Tale of Chlamydia trachomatis and Sexually Transmitted Viruses

The global incidence of sexually transmitted infections (STIs) remains high, with the World Health Organization (WHO) estimating that over 1 million people acquire STIs daily. STIs can lead to infertility, pregnancy complications, and cancers. Co-infections with multiple pathogens are prevalent among individuals with an STI and can lead to heightened infectivity and more severe clinical manifestations. Chlamydia trachomatis (CT) is the most reported bacterial STI worldwide in both men and women, and several studies have demonstrated co-infection of CT with viral and other bacterial STIs. CT is a gram-negative bacterium with a unique biphasic developmental cycle including infectious extracellular elementary bodies (EBs) and metabolically active intracellular reticulate bodies (RBs). The intracellular form of this organism, RBs, has evolved mechanisms to persist for long periods within host epithelial cells in a viable but non-cultivable state. The co-infections of CT with the most frequently reported sexually transmitted viruses: human immunodeficiency virus (HIV), human papillomavirus (HPV), and herpes simplex virus (HSV) have been investigated through in vitro and in vivo studies. These research studies have made significant strides in unraveling the intricate interactions between CT, these viral STIs, and their eukaryotic host. In this review, we present an overview of the epidemiology of these co-infections, while specifically delineating the underlying mechanisms by which CT influences the transmission and infection dynamics of HIV and HSV. Furthermore, we explore the intricate relationship between CT and HPV infection, with a particular emphasis on the heightened risk of cervical cancer. By consolidating the current body of knowledge, we provide valuable insights into the complex dynamics and implications of co-infection involving CT and sexually transmitted viruses.

Chaperonin: Co-chaperonin Interactions

Co-chaperonins function together with chaperonins to mediate ATP-dependent protein folding in a variety of cellular compartments. Chaperonins are evolutionarily conserved and form two distinct classes, namely, group I and group II chaperonins. GroEL and its co-chaperonin GroES form part of group I and are the archetypal members of this family of protein folding machines. The unique mechanism used by GroEL and GroES to drive protein folding is embedded in the complex architecture of double-ringed complexes, forming two central chambers that undergo conformational rearrangements that enable protein folding to occur. GroES forms a lid over the chamber and in doing so dislodges bound substrate into the chamber, thereby allowing non-native proteins to fold in isolation. GroES also modulates allosteric transitions of GroEL. Group II chaperonins are functionally similar to group I chaperonins but differ in structure and do not require a co-chaperonin. A significant number of bacteria and eukaryotes house multiple chaperonin and co-chaperonin proteins, many of which have acquired additional intracellular and extracellular biological functions. In some instances, co-chaperonins display contrasting functions to those of chaperonins. Human HSP60 (HSPD) continues to play a key role in the pathogenesis of many human diseases, in particular autoimmune diseases and cancer. A greater understanding of the fascinating roles of both intracellular and extracellular Hsp10 on cellular processes will accelerate the development of techniques to treat diseases associated with the chaperonin family.

Impact of nutrients on the function of the chlamydial Rsb partner switching mechanism

The obligate intracellular bacterial pathogen Chlamydia trachomatis is a leading cause of sexually transmitted infections and infectious blindness. Chlamydia undergo a biphasic developmental cycle alternating between the infectious elementary body (EB) and the replicative reticulate body (RB). The molecular mechanisms governing RB growth and RB-EB differentiation are unclear. We hypothesize that the bacterium senses host cell and bacterial energy levels and metabolites to ensure that development and growth coincide with nutrient availability. We predict that a partner switching mechanism (PSM) plays a key role in the sensing and response process acting as a molecular throttle sensitive to metabolite levels. Using purified wild type and mutant PSM proteins, we discovered that metal type impacts enzyme activity and the substrate specificity of RsbU and that RsbW prefers ATP over GTP as a phosphate donor. Immunoblotting analysis of RsbV1/V2 demonstrated the presence of both proteins beyond 20 hours post infection and we observed that an RsbV1-null strain has a developmental delay and exhibits differential growth attenuation in response to glucose levels. Collectively, our data support that the PSM regulates growth in response to metabolites and further defines biochemical features governing PSM-component interactions which could help in the development of novel PSM-targeted therapeutics.

Initial Characterization of the Two ClpP Paralogs of Chlamydia trachomatis Suggests Unique Functionality for Each

Members of Chlamydia are obligate intracellular bacteria that differentiate between two distinct functional and morphological forms during their developmental cycle, elementary bodies (EBs) and reticulate bodies (RBs). EBs are nondividing small electron-dense forms that infect host cells. RBs are larger noninfectious replicative forms that develop within a membrane-bound vesicle, termed an inclusion. Given the unique properties of each developmental form of this bacterium, we hypothesized that the Clp protease system plays an integral role in proteomic turnover by degrading specific proteins from one developmental form or the other. Chlamydia spp. have five uncharacterized clp genes, clpX, clpC, two clpP paralogs, and clpB In other bacteria, ClpC and ClpX are ATPases that unfold and feed proteins into the ClpP protease to be degraded, and ClpB is a deaggregase. Here, we focused on characterizing the ClpP paralogs. Transcriptional analyses and immunoblotting determined that these genes are expressed midcycle. Bioinformatic analyses of these proteins identified key residues important for activity. Overexpression of inactive clpP mutants in Chlamydia spp. suggested independent function of each ClpP paralog. To further probe these differences, we determined interactions between the ClpP proteins using bacterial two-hybrid assays and native gel analysis of recombinant proteins. Homotypic interactions of the ClpP proteins, but not heterotypic interactions between the ClpP paralogs, were detected. Interestingly, protease activity of ClpP2, but not ClpP1, was detected in vitro This activity was stimulated by antibiotics known to activate ClpP, which also blocked chlamydial growth. Our data suggest the chlamydial ClpP paralogs likely serve distinct and critical roles in this important pathogen.IMPORTANCE Chlamydia trachomatis is the leading cause of preventable infectious blindness and of bacterial sexually transmitted infections worldwide. Chlamydiae are developmentally regulated obligate intracellular pathogens that alternate between two functional and morphologic forms, with distinct repertoires of proteins. We hypothesize that protein degradation is a critical aspect to the developmental cycle. A key system involved in protein turnover in bacteria is the Clp protease system. Here, we characterized the two chlamydial ClpP paralogs by examining their expression in Chlamydia spp., their ability to oligomerize, and their proteolytic activity. This work will help understand the evolutionarily diverse Clp proteases in the context of intracellular organisms, which may aid in the study of other clinically relevant intracellular bacteria.

Transformation of Chlamydia: current approaches and impact on our understanding of chlamydial infection biology

The intonation "The king is dead, long live the king" aptly describes the state of Chlamydia research. Genetic-based approaches are rapidly replacing correlative strategies to provide new insights. We describe how current transformation technologies are enhancing progress in understanding Chlamydia infection biology and present key opportunities for further development.

Advances and Obstacles in the Genetic Dissection of Chlamydial Virulence

Obligate intracellular pathogens in the family Chlamydiaceae infect taxonomically diverse eukaryotes ranging from amoebae to mammals. However, many fundamental aspects of chlamydial cell biology and pathogenesis remain poorly understood. Genetic dissection of chlamydial biology has historically been hampered by a lack of genetic tools. Exploitation of the ability of chlamydia to recombine genomic material by lateral gene transfer (LGT) ushered in a new era in chlamydia research. With methods to map mutations in place, genetic screens were able to assign functions and phenotypes to specific chlamydial genes. Development of an approach for stable transformation of chlamydia also provided a mechanism for gene delivery and platforms for disrupting chromosomal genes. Here, we explore how these and other tools have been used to test hypotheses concerning the functions of known chlamydial virulence factors and discover the functions of completely uncharacterized genes. Refinement and extension of the existing genetic tools to additional Chlamydia spp. will substantially advance understanding of the biology and pathogenesis of this important group of pathogens.