Biology subjects

Petit, D.

Publications and source records attributed to Petit, D..

3 recordsLinked to original sources

bioRxiv2025

Novel polymer fixed-target microfluidic platforms with an ultra-thin moisture barrier for serial macromolecular crystallography

The advent of ultrabright fourth generation X-ray light sources, including X-ray free-electron lasers (XFELs) and diffraction limited synchrotrons, has significantly advanced the field of serial macromolecular protein crystallography (SX). SX experiments demand a continuous supply of fresh microcrystalline sample, ideally while minimizing overall sample consumption. Here, we introduce a novel, robust, and user-friendly polymer film technology that can be assembled in various configurations to encapsulate protein microcrystals and provide sample support for SX. This system provides an efficient hydration barrier over extended durations while maintaining an exceptionally low X-ray background. We have validated this technology by assessing hydration retention under both ambient and ultra-high vacuum conditions, and by evaluating its mechanical stability under XFEL pulses. Furthermore, we have demonstrated the effectiveness of this approach in two room-temperature serial crystallography studies to determine the structure of a 24 kDa Rapid Encystment Phenotype (REP24) protein from Franciscella tularensis.

biophysics↗

bioRxiv2023

APP substrate ectodomain defines A beta length by restraining gamma-secretase processivity and facilitating product release

Sequential proteolysis of the amyloid precursor protein (APP) by {gamma}-secretases (GSECs) generates amyloid-{beta} (A{beta}) and defines the proportion of short-to-long A{beta} peptides, which is tightly connected to Alzheimers disease (AD) pathogenesis. Here, we study the mechanism controlling substrate processing by GSECs and defining product length. We found that polar interactions established by the APPC99 ectodomain (ECD), involving but not limited to its juxtamembrane region, restrain both the extent and degree of GSEC processive cleavage by destabilizing enzyme-substrate (E-S) interactions. We show that increasing hydrophobicity at APPC99-ECD - due to mutation or ligand binding - attenuates this substrate-driven product release mechanism, and rescues the effects that AD pathogenic variants exert on A{beta} profiles. In addition, our study reveals that APPC99-ECD facilitates the paradoxical production of longer A{beta}s caused by some GSEC inhibitors that act as high-affinity competitors to the substrate. These findings assign a pivotal role to the substrate ECD in the sequential proteolysis by GSEC and suggest it as a sweet spot for the potential design of APP targeting compounds selectively promoting its processing by GSEC.

biochemistry↗

bioRxiv2021

A Fatty Acid Anabolic Pathway in Specialized-Cells Remotely Controls Oocyte Activation in Drosophila

Pheromone-mediated partner recognition is crucial for maintenance of animal species. Here, we discover a metabolic link between pheromone and gamete physiology. In female genital tract, oocyte maturation is arrested at a specific meiotic-phase. Release of this arrest, called oocyte-activation, is triggered by a species-dependent signal. We show in Drosophila melanogaster that oenocytes, which produce the fatty acids (FAs) used as precursors of cuticular hydrocarbons (CHCs), including pheromones, are also essential for oocyte activation. We identified a set of FA-anabolic enzymes required within oenocytes for the synthesis of a particular FA that is not a CHC precursor but controls oocyte activation. Our study thus reveals that two tightly linked FA-anabolic pathways act in parallel, one to produce sexual pheromones, the other to initiate embryonic development. Given that pheromone-deficient Drosophila melanogaster females are highly attractive for males irrespective of their species, this oenocyte function might have evolved to prevent hybrid development.

physiology↗