Biology subjects

Sawin, K.

Publications and source records attributed to Sawin, K..

2 recordsLinked to original sources

bioRxiv2018

Fission yeast NDR/LATS kinase Orb6 regulates exocytosis via phosphorylation of exocyst complex

NDR/LATS kinases regulate multiple aspects of cell polarity and morphogenesis from yeast to mammals, but few of their substrates are known. Fission yeast NDR/LATS kinase Orb6 has been proposed to control cell polarity via spatial regulation of Gef1, a guanine nucleotide exchange factor for the small GTPase Cdc42. Here we show that Orb6 plays a critical role as a positive regulator of exocytosis, independent of Gef1. Through Orb6 inhibition in vivo and quantitative global phosphoproteomics, we identify several proteins involved in membrane trafficking as Orb6 targets, and we confirm Sec3 and Sec5, conserved components of the exocyst complex, as substrates of Orb6 both in vivo and in vitro. Our results suggest that Orb6 kinase activity is crucial for exocyst localization to actively-growing cell tips and for exocyst activity during septum dissolution after cytokinesis. We further show that Orb6 phosphorylation of Sec3 serine-201 contributes to exocyst function in parallel with exocyst protein Exo70. We propose that Orb6 contributes to polarized growth by regulating membrane trafficking at multiple levels.

cell biology↗

bioRxiv2017

Exportin Crm1 is repurposed as a docking protein to generate microtubule organizing centers at the nuclear pore

Non-centrosomal microtubule organizing centers (MTOCs) are important for microtubule organization in many cell types. In fission yeast Schizosaccharomyces pombe, the protein Mto1, together with partner protein Mto2 (Mto1/2 complex), recruits the {gamma}-tubulin complex to multiple non-centrosomal MTOCs, including the nuclear envelope (NE). Here, we develop a comparative-interactome mass spectrometry approach to determine how Mto1 localizes to the NE. Surprisingly, we find that Mto1, a constitutively cytoplasmic protein, docks at nuclear pore complexes (NPCs), via interaction with exportin Crm1 and cytoplasmic FG-nucleoporin Nup146. Although Mto1 is not a nuclear export cargo, it binds Crm1 via a nuclear export signal-like sequence, and docking requires both Ran in the GTP-bound state and Nup146 FG repeats. In addition to determining the mechanism of MTOC formation at the NE, our results reveal a novel role for Crm1 and the nuclear export machinery in the stable docking of a cytoplasmic protein complex at NPCs.

cell biology↗