Identification of tail-binding proteins of Arabidopsis class VIII myosin ATM1 using TurboID proximity labeling and AlphaFold3
Higher plants possess two classes of myosin molecular motors, class XI and class VIII, both unique to the plant lineage. The diverse cellular functions of class XI myosins, including organelle transport and nuclear positioning, have been elucidated largely through systematic identification of cargo adaptor proteins that bind to their globular tail domains (GTDs). In contrast, no proteome-wide screen for class VIII myosin tail-binding proteins has been reported; the few known interacting proteins were each discovered through studies focused on the binding partner rather than on the myosin itself, leaving the full repertoire of class VIII myosin-associated proteins largely unknown. Here, we employed TurboID-based proximity labeling to systematically identify proteins associated with the GTD of the class VIII myosin ATM1 in Arabidopsis thaliana, as this approach covalently biotinylates neighboring proteins in vivo, enabling their identification even after proteolytic degradation during cell lysis. We identified 233 non-redundant candidate ATM1-proximal proteins. Candidates were prioritized by AlphaFold3-based protein complex structure prediction and validated by co-immunoprecipitation. We identified two ATM1-associated proteins: C3H61/AtTZF5, a tandem zinc finger protein involved in mRNA turnover at processing bodies and stress granules; and SFH7, a Sec14-nodulin domain protein that mediates phosphatidic acid transfer from the endoplasmic reticulum to chloroplasts. These findings provide initial evidence linking ATM1 to proteins involved in post-transcriptional gene regulation and interorganellar lipid transport, raising the possibility of previously unrecognized connections between class VIII myosins and these cellular processes.