overexpression-purification-human-cis-prenyltransferase-escherichia

Overexpression and Purification of Human <em>Cis</em>-prenyltransferase in <em>Escherichia coli</em>

Prenyltransferases (PT) are a group of enzymes that catalyze chain elongation of allylic diphosphate using isopentenyl diphosphate (IPP) via multiple ...

Tel Aviv University

β-Cells rely on the islet microenvironment for their functionality and mass. Pericytes, along with endothelial cells, make up the dense islet capillary network. However, although the role of endothelial cells in supporting β-cell homeostasis has been vastly investigated, the role of pericytes remains largely unknown. Here, we focus on contribution of pericytes to β-cell function. To this end, we used a transgenic mouse system that allows diphtheria toxin-based depletion of pericytes. Our results indicate that islets depleted of their pericytes have reduced insulin content and expression. Additionally, isolated islets displayed impaired glucose-stimulated insulin secretion, accompanied by a reduced expression of genes associated with β-cell function. Importantly, reduced levels of the transcription factors MafA and Pdx1 point to β-cell dedifferentiation in the absence of pericytes. Ex vivo depletion of pericytes in isolated islets resulted in a similar impairment of gene expression, implicating their direct, blood flow-independent role in maintaining β-cell maturity. To conclude, our findings suggest that pericytes are pivotal components of the islet niche, which are required for β-cell maturity and functionality. Abnormalities of islet pericytes, as implicated in type 2 diabetes, may therefore contribute to β-cell dysfunction and disease progression.

Islet Pericytes Are Required for β-Cell Maturity.

The membrane-bound sodium-calcium exchanger (NCX) proteins shape Ca(2+) homeostasis in many cell types, thus participating in a wide range of physiological and pathological processes. Determination of the crystal structure of an archaeal NCX (NCX_Mj) paved the way for a thorough and systematic investigation of ion transport mechanisms in NCX proteins. Here, we review the data gathered from the X-ray crystallography, molecular dynamics simulations, hydrogen-deuterium exchange mass-spectrometry (HDX-MS), and ion-flux analyses of mutants. Strikingly, the apo NCX_Mj protein exhibits characteristic patterns in the local backbone dynamics at particular helix segments, thereby possessing characteristic HDX profiles, suggesting structure-dynamic preorganization (geometric arrangements of catalytic residues before the transition state) of conserved α₁ and α₂ repeats at ion-coordinating residues involved in transport activities. Moreover, dynamic preorganization of local structural entities in the apo protein predefines the status of ion-occlusion and transition states, even though Na⁺ or Ca(2+) binding modifies the preceding backbone dynamics nearby functionally important residues. Future challenges include resolving the structural-dynamic determinants governing the ion selectivity, functional asymmetry and ion-induced alternating access. Taking into account the structural similarities of NCX_Mj with the other proteins belonging to the Ca(2+)/cation exchanger superfamily, the recent findings can significantly improve our understanding of ion transport mechanisms in NCX and similar proteins.

Michal Lisnyansky

Department of Physiology and Pharmacology,
Sackler Faculty of Medicine,
Department of Physiology and Pharmacology, Sackler Faculty of Medicine

Tel Aviv University

Overexpression and Purification of Human Cis-prenyltransferase in Escherichia coli

Michal Lisnyansky

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Tel Aviv University

Overexpression and Purification of Human Cis-prenyltransferase in Escherichia coli

Department of Physiology and Pharmacology,
Sackler Faculty of Medicine,
Department of Physiology and Pharmacology, Sackler Faculty of Medicine