# Plasmodium falciparum stomatin-like protein forms a putative complex with a metalloprotease in distinct mitochondrial loci

## TL;DR

This study shows that the STOML protein in malaria parasites is important for asexual growth and localizes with a protease in the mitochondrion.

## Contribution

The study identifies a novel STOML-FtsH complex in P. falciparum mitochondria and its role in asexual blood-stage development.

## Key findings

- Deletion of STOML in P. falciparum causes slower asexual blood-stage development but does not affect sexual-stage development.
- STOML localizes to mitochondrial branching points and forms a complex with the metalloprotease FtsH.
- Structural modeling suggests STOML may form a scaffold similar to bacterial HflK/C proteins.

## Abstract

Members of the Stomatin, Prohibitin, Flotillin and HflK/C (SPFH) protein family form large membrane anchored or spanning complexes and are involved in various functions in different organelles. The human malaria causing parasite Plasmodium falciparum harbors four SPFH proteins, including prohibitin 1 and 2, prohibitin-like protein (PHBL), and stomatin-like protein (STOML), which all localize to the parasite mitochondrion. In the murine model parasite Plasmodium berghei, STOML appears essential for asexual blood-stage (ABS) development and is localized to puncta on mitochondrial branching points in oocyst stages. In this study, we show that deletion of P. falciparum
STOML causes a significant growth defect and slower ABS development, while sexual-stage development remains unaffected. Parasites lacking STOML were not more sensitive to respiratory chain targeting drugs, rendering a function of STOML in respiratory chain assembly unlikely. Epitope tagging of endogenous STOML revealed a distinct punctate localization on branching points and endings of the ABS mitochondrial network. STOML resides in a large protein complex and pulldown experiments identified a zinc dependent metalloprotease, FtsH, as a likely interaction partner. The predicted AlphaFold2 structure of STOML shows high similarity with the bacterial HflK/C, which has been shown to form a large vault-like structure around bacterial FtsH hexamers. Combined, our results suggest that a similar STOML-FtsH complex localized to specific loci of P. falciparum mitochondria facilitates the parasite’s ABS development.

Asexual blood-stage malaria parasites depend on a single mitochondrion that is essential for their growth and survival. This organelle differs from the mitochondria in human cells, making it an attractive drug target. Proteins of the SPFH family are conserved membrane scaffolds that can organize into large protein complexes in the mitochondrion but their roles in malaria parasites remain poorly understood. In this study, we investigate the function of the stomatin-like protein (STOML) in the human malaria parasite Plasmodium falciparum. We show that parasites lacking this protein grow significantly slower in the disease causing asexual blood stage, while sexual-stage development required for transmission to the mosquito remains unaffected. Using fluorescent microscopy, we show that STOML localizes to specific sites on the mitochondrial branching points and branch endings. Biochemical analysis shows that STOML is part of a large protein complex that includes the mitochondrial metalloprotease FtsH. Structural modeling suggests that STOML may assemble into a barrel-like scaffold similar to bacterial complexes that regulate protease activity. Together, our findings shed more light on STOML’s role in parasite mitochondrial function and highlight this protein family for future research.