Biology subjects

Llimargas, M.

Publications and source records attributed to Llimargas, M..

4 recordsLinked to original sources

bioRxiv2024

Different cellular and molecular mechanisms of chitin deposition contribute to the specificity of the two chitin synthases in D. melanogaster.

Chitin is a major component of arthropod extracellular matrices, including the exoskeleton and the midgut peritrophic matrix. It plays a key role in the development, growth and viability of insects. Besides the biological importance of this aminopolysaccharide, chitin also receives a lot of attention for its practical applications in medicine and biotechnology as a superior biopolymer with excellent physicochemical and mechanical properties. Chitin is produced and deposited extracellularly by chitin synthases. Most insects encode two types of chitin synthases, presumably with type A being required for exoskeletons and type B to produce the peritrophic matrix. It is not fully understood, however, which factors contribute to the specificity of each type of chitin synthase. Here we leverage the advantages of Drosophila melanogaster for functional manipulations to evaluate the mechanisms of activity and functional requirements of Kkv (Chitin synthase A) and Chs2 (Chitin synthase B). We first demonstrate that Chs2 is expressed and required in a region in the larval proventriculus that produces the chitin deposited in the peritrophic matrix. We then analyse whether the two chitin synthases can replace each other. We also investigate the subcellular localisation of these chitin synthases in different tissues and their ability to deposit chitin in combination with known auxiliary proteins. Our results indicate that the two different chitin synthases are not functionally equivalent, and that they use specific cellular and molecular mechanisms to deposit chitin. We suggest that the specificity of the different insect chitin synthases may underly the production of chitin polymers with different properties, conferring different physiological activities to the extracellular matrices.

developmental biology↗

bioRxiv2022

An allosteric switch between the activation loop and a c-terminal palindromic phospho-motif controls c-Src function

Auto-phosphorylation controls the transition between discrete functional and conformational states in protein kinases, yet the structural and molecular determinants underlaying this fundamental process remain unclear. Here we show that c-terminal Tyr 530 is a de facto c-Src auto-phosphorylation site with slow time-resolution kinetics and strong intermolecular component. On the contrary, activation-loop Tyr 419 undergoes fast kinetics and a cis-to-trans phosphorylation-switch that controls c-terminal Tyr 530 auto-phosphorylation, enzyme specificity and strikingly, c-Src non-catalytic function as a substrate. In line with this, we visualize by X-ray crystallography a snapshot of Tyr 530 intermolecular phosphorylation in which a c-terminal palindromic phospho-motif flanking Tyr 530 on the susbtrate molecule engages the P-loop of the active kinase for ready entry prior catalysis. Perturbation of the phospho-motif accounts for c-Src disfunction as indicated by viral and a colorectal cancer (CRC) associated c-terminal deleted variants. We show that c-terminal residues 531 to 536 are required for c-Src Tyr 530 and global auto-phosphorylation, and this detrimental effect is caused by the susbtrate molecule inhibiting allosterically the active kinase. Our work reveals a bi-directional crosstalk between the activation and c-terminal segments that controls the allosteric interplay between susbtrate and enzyme acting kinases during auto-phosphorylation HighlightsO_LIA bi-directional phospho-switch connecting the activation and c-terminal segments controls c-Src function C_LIO_LIActivation-loop Tyr 419 is required for c-terminal Tyr 530 auto-phosphorylation, enzyme specificity and non-catalytic function as a substrate C_LIO_LIBiochemical and structural visualization of c-Src Tyr 530 intermolecular auto-phosphorylation C_LIO_LIA double-phosphorylated c-Src on both the activation and c-terminal segments is a fully active protein C_LIO_LICancer associated c-terminal deleted variants inhibit allosterically c-Src activity by a dominant negative effect C_LI

biochemistry↗

bioRxiv2022

Dissecting the roles of Expansion/Rebuf and the chitin synthase Krotzkopf Verkehrt in chitin deposition in Drosophila

Chitin is a highly abundant polymer in nature and a principal component of apical extracellular matrices in insects. In addition, chitin has proved to be an excellent biomaterial with multiple applications. In spite of its importance, the molecular mechanisms of chitin biosynthesis and chitin structural diversity are not fully elucidated yet. To investigate these issues, we use Drosophila as a model. We previously showed that chitin deposition in ectodermal tissues requires the concomitant activities of the chitin synthase enzyme Kkv and the functionally interchangeable proteins Exp and Reb. Here we carry out a cellular and molecular analysis of chitin deposition and we show that chitin polymerisation and chitin translocation to the extracellular space are uncoupled. We find that Kkv activity in chitin translocation, but not in polymerisation, requires the activity of Exp/Reb, and in particular of its conserved N-MH2 domain. The activity of Kkv in chitin polymerisation and translocation correlate with Kkv subcellular localisation, and in absence of Kkv-mediated extracellular chitin deposition, chitin accumulates intracellularly as membrane-less punctae. Furthermore, we find that Kkv and Exp/Reb display a largely complementary pattern at the apical domain, and that Exp/Reb activity regulates the topological distribution of Kkv at the apical membrane. We propose a model in which Exp/Reb regulates the organisation of Kkv complexes at the apical membrane which, in turn, regulates the function of Kkv in extracellular chitin translocation.

developmental biology↗

bioRxiv2018

Anisotropic Crb accumulation, modulated by Src42A, orients epithelial tube growth in Drosophila

Size control of internal tubular organs, such as the lungs or vascular system, is critical for proper physiological activity and to prevent disease or malformations. This control incorporates the intrinsic physical anisotropy of tubes to generate proportionate organs that match their function. The exact mechanisms underlying tube size control and how tubular anisotropy is translated at the cellular level are still not fully understood. Here we investigate these mechanisms using the Drosophila tracheal system. We show that the apical polarity protein Crumbs transiently accumulates anisotropically at longitudinal cell junctions during tube elongation. We provide evidence indicating that the accumulation of Crumbs in specific apical domains correlates with apical surface growth. Hence, we propose that the anisotropic accumulation of Crb at the cellular level promotes a bias towards longitudinal membrane growth, orienting cell elongation and, as a consequence, longitudinal growth at the tissue level. We find that Src42A promotes Crb anisotropic accumulation, thereby identifying the first polarised cell behaviour downstream of Src42A. Our results indicate that Src42A activity favours a higher turnover of Crb protein at longitudinal junctions, possibly through a mechanism regulating protein trafficking and/or recycling. We propose a model where Src42A would sense the inherent anisotropic mechanical tension of the tube and translate it into a polarised Crumbs-mediated membrane growth, orienting longitudinal tube growth. This work provides new insights into the key question of how organ growth is controlled and polarised and unveils the function of two conserved proteins, Crumbs and Src42A, with important roles in development and homeostasis as well as in disease, in this biological process.

developmental biology↗