Biology subjects

Giska, F.

Publications and source records attributed to Giska, F..

3 recordsLinked to original sources

bioRxiv2023

Direct determination of oligomeric organization of integral membrane proteins and lipids from intact customizable bilayer

Hierarchical organization of integral membrane proteins (IMP) and lipids at the membrane is essential for regulating myriad downstream signaling. A quantitative understanding of these processes requires both detections of oligomeric organization of IMPs and lipids directly from intact membranes and determination of key membrane components/properties that regulate them. Addressing this, we have developed a platform that enables native mass spectrometry (nMS) analysis of IMP-lipid complexes directly from intact and customizable lipid membranes. Both the lipid composition and membrane properties (such as curvature, tension, fluidity) of these bilayers can be precisely customized to a target membrane. Subsequent direct nMS analysis of these intact proteo-lipid vesicles can yield the oligomeric states of the embedded IMPs, identify bound lipids, and determine the membrane properties that can regulate the observed IMP-lipid organization. Applying this, we show how lipid binding regulates neurotransmitter release and how membrane composition regulates the functional oligomeric state of a transporter.

biophysics↗

bioRxiv2022

Mitoguardin-2 is a lipid transporter and its lipid transfer ability is required for function

Lipid transport proteins at membrane contact sites, where organelles are closely apposed, are critical in redistributing lipids from the endoplasmic reticulum (ER), where they are made, to other cellular membranes. Such protein mediated transfer is especially important for maintaining organelles disconnected from secretory pathways, like mitochondria. Here we identify mitoguardin-2, a mitochondrial protein at contacts with the ER and/or lipid droplets (LDs), as a lipid transporter. An X-ray structure shows that the C-terminal domain of mitoguardin-2 has a hydrophobic cavity that binds lipids. Mass spectrometry analysis reveals that both glycerophospholipids and free-fatty acids co-purify with mitoguardin-2 from cells, and that each mitoguardin-2 can accommodate up to two lipids. Mitoguardin-2 transfers glycerophospholipids between membranes in vitro, and this transport ability is required for roles both in mitochondrial and LD biology. While it is not established that protein-mediated transfer at contacts plays a role in LD metabolism, our findings raise the possibility that mitoguardin-2 functions in transporting fatty acids and glycerophospholipids at mitochondria-LD contacts.

cell biology↗

bioRxiv2019

Phosphatase PP2C6 negatively regulates phosphorylation status of Pti1b kinase, a regulator of flagellin-triggered immunity in tomato

Plant immune responses, including the production of reactive oxygen species (ROS), are triggered when pattern recognition receptors (PRR) become activated upon detection of microbe-associated molecular patterns (MAMPs). Receptor-like cytoplasmic kinases are key components of PRR-dependent signaling pathways. In tomato two such kinases, Pti1a and Pti1b, are important positive regulators of the plant immune response. However, it is unknown how these kinases control plant immunity at the molecular level, and how their activity is regulated. To investigate these issues, we used mass spectrometry to search for interactors of Pti1b in Nicotiana benthamiana leaves and identified a protein phosphatase, PP2C6. An in vitro pull-down assay and in vivo split luciferase complementation assay verified this interaction. Pti1b was found to autophosphorylate on threonine-233 and this phosphorylation was abolished in the presence of PP2C6. An arginine-to-cysteine substitution at position 240 in the Arabidopsis MARIS kinase was previously reported to convert it into a constitutive-active form. The analogous substitution in Pti1b made it resistant to PP2C6 phosphatase activity, although it still interacted with PP2C6. Treatment of N. benthamiana leaves with the MAMP flg22 induced threonine phosphorylation of Pti1b. Expression of PP2C6, but not a phosphatase-inactive variant of this protein, in N. benthamiana leaves greatly reduced ROS production in response to treatment with MAMPs flg22 or csp22. The results indicate that PP2C6 acts as a negative regulator by dephosphorylating the Pti1b kinase, thereby interfering with its ability to activate plant immune responses.

plant biology↗