Biomolecular condensates of RESP18 homology domain, insulin and proinsulin

MILAGROS B. ABATE; PAMELA TOLEDO; DIEGO SEBASTIAN VAZQUEZ; ALEJO R. GIANOTTI; JUHA TORKKO; MICHELE SOLIMENA; MARIO R. ERMÁCORA

Rosario, Santa Fe

Congreso; L Reunión Anual de la Sociedad Argentina de Biofísica; 2022

Sociedad Argentina de Biofísica

Receptor-type protein-tyrosine phosphatases (RPTPs) are multidomain and transmembrane proteins involved in signalling pathways. ICA512 is a R8 subtype RPTP expressed in peptide-secreting endocrine cells, which is enriched in the membrane of secretory granules (SGs). Insulin is a peptide hormone that regulates glycaemia by balancing glucose uptake in peripheral tissues and its diminished or absent activity leads to all known forms of diabetic diseases. ICA512, among other proteins, is involved in the biogenesis and turnover of insulin SGs in pancreatic β-cells and their depletion, either alone or in combination, strongly reduces insulin SG stores in vitro and in vivo.In the last two decades, an avalanche of studies highlighted the central role of biomolecular condensates - defined as non-stoichiometric and non-covalent clusters of protein molecules ranging from tens of nanometers to microns in size - in membraneless subcellular compartmentalization allowing the spatial and temporal organization and regulation of myriads of biochemical reactions. In previous work, we reported that the N-terminal domain of ICA512, named RESP18 homology domain (residues 35 to 131 of ICA512), co-aggregates in vitro with insulininhibiting its fibrillation. Now we focused on a seven-residue shorter variant denominatedRES18HD124, previously identified as a potential product of cellular processing, in theco-aggregation reaction with insulin and proinsulin - its physiological precursor whichcoexists with insulin and RESP18HD in the trans-Golgi during SG biogenesis. Preliminaryresults suggest that RESP18HD124 forms mesoscopic clusters in solution that evolve intomicron-size objects in the coaggregation reaction with insulin or proinsulin. This mesoscopic clusters are the precursors of amorfous aggregates and could be related with the sorting process in the secretory pathway.