Marcello Miceli

Mutations of the alsin protein have been linked to infantile-onset ascending hereditary spastic paraplegia (IAHSP), a rare neurodegenerative disease. More precisely, the pathological R1611W mutation has been identified in the Vacuolar Protein Sorting 9 (VPS9) domain, which acts as a guanine nucleotide exchange factor (GEF) for Rab5. This mutation results in the expression of tryptophan instead of arginine that alters the oligomeric state of alsin and its GEF functions. Insights into the conformational structure of the wild-type or mutant VPS9 domain may help elucidate the mechanisms involved in the onset of the disease. In this study, we combined in vitro and in silico approaches to elucidate the structure and understand the effects of the R1611W mutation on the isolated VPS9 domain of alsin. This mutation induces conformational changes that alter the local structure of the protein and its ability to oligomerize. This study lays the groundwork for understanding how R1611W alters the VPS9 domain function.

Despite the ubiquity of Membrane Occupation Recognition Nexus (MORN) motifs across diverse species in both eukaryotic and prokaryotic organisms, these protein domains remain poorly characterized. Their significance is underscored in the context of the Alsin protein, implicated in the debilitating condition known as Infantile-onset Ascending Hereditary Spastic Paralysis (IAHSP). Studies have proposed that mutations within the Alsin MORN domain disrupt proper protein assembly, precluding the formation of the requisite tetrameric configuration essential for the protein’s inherent biological activity. However, a comprehensive understanding of the relationship between the biological functions of Alsin and its three-dimensional molecular structure is hindered by the lack of available experimental structures. In this study, by comparing experimentally resolved MORN domains, we predicted a three-dimensional structure for the putative MORN of Alsin. Furthermore, inspired by experimental pieces of evidence from previous studies, we employed the developed models to predict and investigate two homo-dimeric assemblies, characterising their stability. This study’s insights into the three-dimensional structure of the Alsin MORN domain and the stability dynamics of its homo-dimeric assemblies suggest an antiparallel linear configuration stabilized by a non-covalent interaction network. The elucidation of these intricate molecular relationships holds promise for advancing our understanding of pathogenic mechanisms and facilitating the development of treatments for this severe neurodegenerative disorder.

Despite the ubiquity of membrane occupation recognition nexus (MORN) motifs across diverse species in both eukaryotic and prokaryotic organisms, these protein domains remain poorly characterized. Their significance is underscored in the context of the Alsin protein, implicated in the debilitating condition known as infantile‐onset ascending hereditary spastic paralysis (IAHSP). Recent investigations have proposed that mutations within the Alsin MORN domain disrupt proper protein assembly, precluding the formation of the requisite tetrameric configuration essential for the protein's inherent biological activity. However, a comprehensive understanding of the relationship between the biological functions of Alsin and its three‐dimensional molecular structure is hindered by the lack of available experimental structures. In this study, we employed and compared several protein structure prediction algorithms to identify a three‐dimensional structure for the putative MORN of Alsin. Furthermore, inspired by experimental pieces of evidence from previous studies, we employed the developed models to predict and investigate two homo‐dimeric assemblies, characterizing their stability. This study's insights into the three‐dimensional structure of the Alsin MORN domain and the stability dynamics of its homo‐dimeric assemblies suggest an antiparallel linear configuration stabilized by a noncovalent interaction network.

Understanding the intricate interplay between structural features and signal-processing events is crucial for unravelling the mechanisms of biomolecular systems. G protein-coupled receptors (GPCRs), a pervasive protein family in humans, serve a wide spectrum of vital functions. TAS2Rs, a subfamily of GPCRs, play a primary role in recognizing bitter molecules and triggering events leading to the perception of bitterness, a crucial defence mechanism against spoiled or poisonous food. Beyond taste, TAS2Rs function is associated with many diseases as they are expressed in several extra-oral tissues. Since the precise mechanism of TAS2R activation is poorly understood, this work aims to characterize the mechanisms underlying the signal transduction on the recently experimentally solved human TAS2R46 bitter taste receptor using molecular dynamics simulations coupled with network-based analysis. The results show that the allosteric activation of the receptor is associated with more correlated dynamics of the receptor and the formation of an interaction between two helices which mainly convey the signal transferring from the extracellular to the intracellular region. By elucidating the hallmarks of the allosteric network of TAS2R46 under varying conditions (ligand-bound, ligand-free, and transition states), this study has enabled the identification of the unique functional mechanisms of this receptor, thereby establishing a foundation for a more profound characterisation of this intriguing class of receptors. Highlights: The dynamics of TAS2R46 in different states were studied through molecular dynamics and network analysis. The presence of the bitter agonist increases intra-protein correlations. TM3 and TM6 helices mediate the allosteric network in Holo TAS2R46. The rotation of Y241 ^6.48 residue is pivotal in the allosteric network for the Holo TAS2R46.

Infantile-onset Ascending Hereditary Spastic Paralysis, Juvenile Primary Lateral Sclerosis and Juvenile Amyotrophic Lateral Sclerosis are all motor neuron diseases related to mutations on the ALS2 gene, encoding for a 1657 amino acids protein named Alsin. This ~185 kDa multi-domain protein is ubiquitously expressed in various human tissues, mostly in the brain and the spinal cord. Several investigations have indicated how mutations within Alsin’s structured domains may be responsible for the alteration of Alsin’s native oligomerization state or Alsin’s propensity to interact with protein partners. In this review paper, we propose a description of differences and similarities characterizing the above-mentioned ALS2-related rare neurodegenerative disorders, pointing attention to the effects of ALS2 mutation from molecule to organ and at the system level. Known cases were collected through a literature review and rationalized to deeply elucidate the neurodegenerative clinical outcomes as consequences of ALS2 mutations.

The Infantile-onset Ascending Hereditary Spastic Paralysis (IAHSP) is an incurable rare neurodegerative disease related to a mutation-driven aberrant behaviour of the Alsin protein. The lack of information on Alsin atomic structure limits a complete understanding on pathology mechanisms. In this work, molecular modelling techniques have been applied to shed lights on Alsin folding dynamics and misfunction induced by aberrant mutations.