The mitochondrial serine protease High-temperature requirement A2 (HtrA2) has been implicated in a number of physiological conditions such as neurodegenerative disorders and cancer and hence acts as a promising therapeutic target.
To learn more about the role of HtrA2 and its connection with neurodegenerative disorders and cancer, SciSoup spoke with study leader Kakoli Bose and first author Aasna L. Parui about their recent research findings published in the Cell Press journal ‘Structure’.
AUG 01, 2022 | BY RATNESHWAR THAKUR
In the SciSoup interview series “Unfolding Science With SciSoup”, the authors explain the key findings of this study, significance of their new results and its benefits for public or scientific community. Also, don’t miss here listening podcast by Kakoli Bose.
What inspired you for this study?
My lab since its inception works on molecules involved in programmed cell death aka apoptosis and their association with several diseases including cancer. HtrA2 or High temperature requirement protease A2 is one such molecule that is omnipresent in the cell and mediates apoptosis through both caspase-dependent and -independent pathways. This makes it a potential therapeutic target, especially in situations where caspase is non-functional. These were the initial reasons that intrigued me about this protease. However, while working with this serine protease and studying its interaction with different cellular substrates, we found that it has a very complex structural organization and an intricate multimodal mechanism of allosteric activation. Furthermore, the available crystal structures have failed to clearly explain the intricate conformational dynamics and plasticity of all the domains/loops/linkers required to ‘turn on’ the protease into a fully functional molecule. Therefore, we aimed at exploring the intricacies of these different modes of activation adopted by the protease and establish a working model for HtrA2 functioning, which might further lead to devising tailor-made strategies for modulating the protease with desired characteristics in several pathophysiological scenarios.
What is the main finding from your research?
In this study, we report the structural reorganizations required in the conversion of HtrA2 from its basal state (low activity) to its active form and discovered a unique PDZ-domain-led trans-mediated cooperatively-shared energy landscape within the protease ensemble.
How would you explain your research findings and its significance?
Our manuscript aimed at expanding our understanding on the complex allosteric activation of the human proapoptotic serine protease HtrA2 and emphasized on the role of the important protein-protein interaction module PDZ in the allosteric regulation. By generating heterotrimeric HtrA2 variants lacking one or two PDZ domains, we were able to investigate the synergistic coordination of PDZ(s) in the trimeric HtrA2 protein ensemble and establish the existence of inter-subunit PDZ-proteolytic domain networking required for optimal conformation of the active site and efficient substrate degradation. Moreover, in collaboration with Dr. Prasenjit Bhaumik from IIT- Bombay and his student Dr. Vandana Mishra, we were able to solve the first crystal structure of the HtrA2 trimer deprived of all PDZ domains and ascertain the importance of a small modulatory domain in the maintenance of protein ensemble architecture. Therefore, apart from providing cues for devising structure-guided therapeutic strategies, this study establishes a physiologically relevant working model of complex allosteric regulation that can shape the future therapeutic interventions for such a multi-tasking protease.
Why is this study interesting?
This is a beautiful study that presents the visualization of allosteric communication within protein ensembles. Engineering a particular protein ensemble with subunits of different lengths is quite tricky, especially when the protein has odd-numbered subunits. We have successfully standardized the strategy to generate and separate closely-related heterotrimeric protein variants which have similar biophysical and biochemical properties. Moreover, how one can increase the resolution of a poorly diffracting protein crystal was also a part of this collaborative study and we have productively obtained some wonderful results in terms of decoding the structural aspects of the HtrA2 protein.
How will this research be useful to the public or Scientific Community?
HtrA2 has been implicated in a number of physiological conditions such as neurodegenerative disorders and cancer and hence acts as a promising therapeutic target. Biotechnology firms are now focusing their search paradigm towards the hidden regulatory pockets of any particular protein rather than targeting their active sites directly. Therefore, unraveling the multimodal allosteric activation mechanism of HtrA2 that caters to the recognition and cleavage of separate substrates in various cellular processes might eventually lead to decoding the intricacies of both the canonical and non-canonical HtrA2-mediated apoptotic pathways. Thus, understanding the minutiae of this mechanism in a step-wise manner would help devise its tailor-made modulators for disease intervention.
Journal Reference:
Inter-subunit crosstalk via PDZ synergistically governs allosteric activation of proapoptotic HtrA2
Disclaimer:
SciSoup claims no competing interest.
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"Dr. Bose and her colleagues have shown that a complex network of interactions among amino acids in the protein HtrA2 result in exquisite control of the enzymatic activity of this important protein. The interactions are fine-tuned to cellular conditions so that subtle changes affect key molecular decisions as to whether a cell lives or dies. Not only does Dr. Bose’s work further our understanding of how large protein complexes work, but they also provide new avenues for therapeutic intervention-- Prof. Allan Clay Clark, University of Texas at Arlington."