Journal of Bacteriology & Parasitology

N-terminal targeting sequences and coding sequences act in concert to determine the localization and trafficking pathway of apicoplast proteins in Toxoplasma gondii

10^th International Confernce on Parasitology, Microbiology and Infection Control

November 08-09, 2022 | Webinar

Sofia Anjum

Indian Institute of Technology Bombay, India

Scientific Tracks Abstracts: J Bacteriol Parasitol

Abstract:

Statement of the problem: The apicoplast, a secondary endosymbiont, is present in most apicomplexan parasites, including Toxoplasma gondii and Plasmodium species. Apicoplast proteins are trafficked from the Endoplasmic Reticulum (ER) to the apicoplast by two pathways in T. gondii: Golgi-dependent and Golgi-independent. Proteins exclusively localizing to the apicoplast (e.g. TgACP) follow a Golgi-independent pathway, while proteins dually targeted to the apicoplast and the mitochondrion (TgTPx1/2, TgSOD2, TgACN) follow a Golgi-dependent pathway. Previously we showed that dually localized proteins contain N-terminal ambiguous signal sequences that direct them to the apicoplast and the mitochondrion. Based on these results, we asked (1) whether ambiguous signal sequences can drive dual targeting when fused with other proteins and (2) whether these signal sequences are sufficient to direct any protein via a Golgi-dependent route to the apicoplast. Methodology & Theoretical Orientation: We generated constructs by swapping the N-termini of dually localized proteins with proteins (devoid of signal sequences) that use different routes to the apicoplast. The pathway taken by the fusion protein was analyzed using an ER retrieval signal, i.e. HDEL, that will only affect the localization of the protein taking a Golgi-dependent route. Findings: The signal sequence of dually localized proteins targeted these chimeric proteins to either the apicoplast or the mitochondrion, with dual localization seen only in a fraction of the cells. These proteins showed no alteration in the localization even after the addition of the HDEL sequence, indicating a Golgi-independent route. Conclusion & Significance: These results reveal that dually localized proteins contain signal sequences throughout the proteins. Any mismatch will direct the protein through the Golgi-independent route as a default pathway. Our data provides a cautionary message for researchers using the N-terminal sequences of dually targeted proteins for directing reporters to the apicoplast. We also suggest that the signal sequences of dually targeted proteins may have helped in sampling different organellar compartments during establishment of the early apicoplast endosymbiont.

Biography :

Sofia Anjum is currently a PhD student at the Indian Institute of Technology Bombay. Her research primarily focuses on understanding the fundamental aspect of the existence of two different protein trafficking pathways to the apicoplast, an essential organelle in apicomplexan parasites. She is interested to know whether the N-terminal signals are the distinguishing features of the two pathways and if there is any functional relevance of this in the parasite’s biology. She has established gene knockout studies in the lab as she plans to knock down endogenous apicoplast proteins and replace them with proteins following different trafficking pathways. This will provide insights into the role of these pathways in protein function and, ultimately, parasite fitness.