5 research outputs found
Computational and Structural Evidence for Neurotransmitter-mediated Modulation of the Oligomeric States of Human Insulin in Storage Granules
Human insulin is a pivotal protein hormone controlling metabolism, growth and ageing, and whose malfunctioning underlies diabetes, some cancers and neuro-degeneration. Despite its central position in human physiology, the in vivo oligomeric state and conformation of insulin in its storage granules in the pancreas are not known. In contrast, many in vitro structures of hexamers of this hormone are available, which fall into three conformational states: T6, T3Rf3 and R6. As there is strong evidence for accumulation of neurotransmitters, such as serotonin and dopamine, in insulin storage granules in pancreatic β-cells, we probed by molecular dynamics (MD) and protein crystallography (PC) if these endogenous ligands affect and stabilize insulin oligomers. Parallel studies independently converged on the observation that serotonin binds well within the insulin hexamer (site I), stabilizing it in the T3R3 conformation. Both methods indicated serotonin binding on the hexamer surface (site III) as well. MD, but not PC, indicated that dopamine was also a good site III ligand. Some of the PC studies also included arginine, which may be abundant in insulin granules upon processing of pro-insulin, and stable T3R3 hexamers loaded with both serotonin and arginine were obtained. The MD and PC results were supported further by in solution spectroscopic studies with R-state specific chromophore. Our results indicate that the T3R3 oligomer is a plausible insulin pancreatic storage form, resulting from its complex interplay with neurotransmitters, and pro-insulin processing products. These findings may have implications for clinical insulin formulations
Commonality of Virulence-Promoting Function in Rhodococcus equi Virulence Associated Proteins (Vaps)
Rhodococcus equi is a Gram-positive facultative intracellular pathogen associated with life-threatening bronchopneumonial disease in foals. Key to R. equi’s intracellular survival in host macrophages is the production of virulence associated proteins (Vaps). Numerous vap genes are found on virulence plasmids isolated from different species, and the Vaps share a high degree of sequence identity. VapA has been extensively studied, and although vapK and vapN genes from other R. equi virulence plasmids have been shown to be essential for R. equi intracellular survival, their mode of action is less characterised. We, therefore, examined whether VapK and VapN worked mechanistically in the same way as VapA. Indeed, like VapA, VapK and VapN neutralised lysosomal pH and reduced lysosomal hydrolase activity. A loss of VapA and R. equi virulence could be regained by the presence of either VapK or VapN. The acid-neutralisation activity was also observed to a lesser extent with VapB. There was a differential activity across these virulence-promoting Vaps with the most “acid-neutralising” activity found with VapN, then VapA and K, and finally VapB. These data suggest that VapA production, which is often found in equine infections, can be substituted by VapK and B (produced by plasmids often found in porcine species) or VapN (produced by plasmids often isolated in bovine and human samples). These data imply that the molecular mechanism(s) that VapA uses to neutralise lysosomal acidity should also be seen in VapN and K which will help guide researchers in identifying their precise mode of action and aid the future development of targeted therapeutics
Can Arginine Inhibit Insulin Aggregation? A Combined Protein Crystallography, Capillary Electrophoresis, and Molecular Simulation Study
The oligomeric state of the storage form of human insulin in the pancreas, which may be affected by several endogenous components of β-cell storage granules such as arginine, is not known. Here, the effect of arginine on insulin oligomerization is investigated independently by protein crystallography, molecular dynamics simulations, and capillary electrophoresis. The combined results point to a strong effect of ionic strength on insulin assembly. Molecular simulations and electrophoretic measurements at low/mM salt concentrations show no significant effect of arginine on insulin aggregation. In contrast, crystallographic data at high/molar ionic strength indicate inhibition of insulin hexamerization by arginine due to its binding at the site relevant for intermolecular contacts, which was also observed in MD simulations. Our results thus bracket the in vivo situation in pancreatic β-cell storage granules, where the ionic strength is estimated to be in the hundreds of millimolar to submolar range. The present findings add to a molecular understanding of in vivo insulin oligomerization and storage, with additional implications for insulin stability in arginine-rich injections
Can Arginine inhibit Insulin Aggregation? A Combined Protein Crystallography, Capillary Electrophoresis, and Molecular Simulation Study
The oligomeric state of the storage form of human insulin in pancreas, which may be affected by
several endogenous components of beta-cells storage granules such as arginine, is not known. Here,
the effect of arginine on insulin oligomerisation is investigated independently by protein
crystallography, molecular dynamics simulations and capillary electrophoresis. The combined
results point to a strong effect of ionic strength on insulin assembly. Molecular simulations and
electrophoretic measurements at low/mM salt concentrations show no significant effect of arginine
on insulin aggregation. In contrast, crystallographic data at high/molar ionic strength indicate
inhibition of insulin hexamerization by arginine due to its binding at site relevant for
intermolecular contacts, which was also observed in MD simulations. Our results thus bracket the
in vivo situation in pancreatic beta-cells storage granules, where the ionic strength is estimated to be
in the hundreds of millimolar to sub-molar range. The present findings add to molecular
understanding of in vivo insulin oligomerization and storage, with additional implications for
insulin stability in arginine-rich injections.
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