Bsp1, a fungal CPI motif protein, regulates actin filament capping in endocytosis and cytokinesis
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Abstract
The capping of barbed filament ends is a fundamental mechanism for actin regulation. Capping protein controls filament growth and actin turnover in cells by binding to the barbed ends of the filaments with high affinity and slow off-rate. The interaction between capping protein and actin is regulated by capping protein interaction (CPI) motif proteins. We identified a novel CPI motif protein, Bsp1, which is involved in cytokinesis and endocytosis in budding yeast. We demonstrate that Bsp1 is an actin binding protein with a high affinity for capping protein via its CPI motif. In cells, Bsp1 regulates capping protein at endocytic sites and is a major recruiter of capping protein to the cytokinetic actin ring. Lastly, we define Bsp1-related proteins as a distinct fungi-specific CPI protein group. Our results suggest that Bsp1 promotes actin filament capping by the capping protein. This study establishes Bsp1 as a new capping protein regulator and promising candidate to regulate actin networks in fungi.
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Abstract
Really nice & convincing work! I really enjoyed reading this paper. Its fascinating how these mutations can have such a broad impact on different parts of the endocytic machinery but with no measurable impact on the accumulation of actin in patches or the internalization of vesicles! Thank you for sharing it on here!
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he analysis of Pan1 motility showed that membrane invagination and vesicleformation are not affected by the deletion of Bsp1 (Fig. 3C).
Did you compare the intensity of tagged Pan1? it looks like it might be brighter in the bsp1 mutant compared to WT.
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Next we wanted to study if Bsp1 interacts directly with CP.
Its probably worth noting that in Drees 2001 they state "Ypr171w also interacted with Cap1, the α subunit of the yeast actin filament capping protein", but the evidence you provide is definitely much more convincing.
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one of our mutants showed complete mislocalization,indicating that the proline-rich N-terminal part of the protein also has a role in the localizationof Bsp1.
Very cool! Did you try to make the 408-470 peptide in vivo as well? Since the inclusion of the WH2-like domain enhances patch localization, it'd be neat to see if the domain is sufficient to recruit the peptide to the patches. Meaning it could be recruited through both the proline-rich region and the WH2-like domain. Or alternatively if the WH2-dependent enhancement is because of a feedback loop of sorts.
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Theputative WH2 and CPI sequences together with the localization of Bsp1 actin structuressuggest a role in actin regulation
It could be useful to sight its reported interactions with Bzz1, CAP1, Las17, Lsb3, RSV161, RSV167, Sla1, and YSC84 (several sources logged at yeastgenome.org)
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Bsp1 localizes to endocytic actin patches and cytokinetic actin rings (Drees et al., 2001;Wright et al., 2008; Tonikian et al., 2009).
This was also shown in Wicky et al 2003 where they also showed actin patch defects when BSP1 was overexpressed. (https://doi.org/10.1016/S0014-5793(03)00067-X)
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