Genetically engineered transfusable platelets using mRNA lipid nanoparticles.

Platelet transfusions are essential for managing bleeding and hemostatic dysfunction and could be expanded as a cell therapy due to the multifunctional role of platelets in various diseases. Creating these cell therapies will require modifying transfusable donor platelets to express therapeutic proteins. However, there are currently no appropriate methods for genetically modifying platelets collected from blood donors. Here, we describe an approach using platelet-optimized lipid nanoparticles containing mRNA (mRNA-LNP) to enable exogenous protein expression in human and rat platelets. Within the library of mRNA-LNP tested, exogenous protein expression did not require nor correlate with platelet activation. Transfected platelets retained hemostatic function and accumulated in regions of vascular damage after transfusion into rats with hemorrhagic shock. We expect this technology will expand the therapeutic potential of platelets.

Large conformational dynamics in Band 3 protein: Significance for erythrocyte senescence signalling.

Band 3 (Anion Exchanger 1, AE1), the predominant protein of erythrocyte membranes, facilitates Cl-/HCO3- exchange and anchors the plasma membrane to the cytoskeleton. The Band 3 crystal structure revealed the amino acid 812-830 region as intracellular, conflicting with protein chemical data that suggested extracellular disposition. Further, circulating senescent cell auto-antibody that cannot enter erythrocytes, binds two regions of Band 3: residues 538-554 and 812-830. To reconcile this discrepancy, we assessed localization of residues 812-830 with Band 3 expressed in HEK293 cells and human erythrocytes, using chemical labeling probes and an antibody against residues 812-830. Antibody and chemical probes revealed reorientation of 812-830 region between extracellular and intracellular. This dramatic conformational change is an intrinsic property of the Band 3 molecule, occurring when expressed in HEK293 cells and without the damage that occurs during erythrocyte circulation. Conditions used to crystallize Band 3 for structural determination did not alter conformational dynamics. Collectively, these data reveal large Band 3 conformational dynamics localized to a region previously identified as an erythrocyte senescence epitope. Surface exposure of the senescence epitope (812-830), limited by conformational dynamics, may act as the "molecular clock" in erythrocyte senescence.

The necdin interactome: evaluating the effects of amino acid substitutions and cell stress using proximity-dependent biotinylation (BioID) and mass spectrometry.

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder caused by the loss of function of a set of imprinted genes on chromosome 15q11-15q13. One of these genes, NDN, encodes necdin, a protein that is important for neuronal differentiation and survival. Loss of Ndn in mice causes defects in the formation and function of the nervous system. Necdin is a member of the melanoma-associated antigen gene (MAGE) protein family. The functions of MAGE proteins depend highly on their interactions with other proteins, and in particular MAGE proteins interact with E3 ubiquitin ligases and deubiquitinases to form MAGE-RING E3 ligase-deubiquitinase complexes. Here, we used proximity-dependent biotin identification (BioID) and mass spectrometry (MS) to determine the network of protein-protein interactions (interactome) of the necdin protein. This process yielded novel as well as known necdin-proximate proteins that cluster into a protein network. Next, we used BioID-MS to define the interactomes of necdin proteins carrying coding variants. Variant necdin proteins had interactomes that were distinct from wildtype necdin. BioID-MS is not only a useful tool to identify protein-protein interactions, but also to analyze the effects of variants of unknown significance on the interactomes of proteins involved in genetic disease.

Role of N-glycosylation in the expression of human SLC26A2 and A3 anion transport membrane glycoproteins 1.

The human solute carrier 26 (SLC26) gene family of anion transporters consists of 10 members (SLC26A1-A11, A10 being a pseudogene) that encode membrane glycoproteins with 14 transmembrane segments and a C-terminal cytoplasmic sulfate transporter anti-sigma antagonist domain. Thus far, mutations in eight members of the SLC26 family (A1-A6, A8, and A9) have been linked to diseases in humans. Our goal is to characterize the role of N-glycosylation and the effect of mutations in SLC26A2 and A3 proteins on their functional expression in transfected HEK-293 cells. We found that certain mutants were retained in the endoplamic reticulum via an interaction with the lectin chaperone calnexin. Some could escape protein quality control and traffic to the cell surface upon removal of the N-glycosylation sites. Furthermore, we found that loss of N-glycosylation reduced expression of SLC26A2 at the cell surface. Loss of N-glycosylation had no effect on the stability of SLC26A3, yet resulted in a profound decrease in transport activity. Thus, N-glycosylation plays three roles in the functional expression of SLC26 proteins: (1) to retain misfolded proteins in the endoplamic reticulum, (2) to stabilize the protein at the cell surface, and (3) to maintain the transport protein in a functional state.

Molecular mechanism for the red blood cell senescence clock.

Lacking protein synthesis machinery and organelles necessary for autophagy or apoptosis, aged red blood cells (RBCs) are marked by circulating auto-antibodies for macrophage-mediated clearance. The antigen recognized by these auto-antibodies is the major protein of the RBC membrane, Band 3. To ensure regulation and specificity in clearance, the molecular "clock" must mark senescent cells in a way that differentiates them from younger cells, to prevent premature clearance. Predominant models of Band 3 senescence signaling are reviewed, and merits are discussed in light of the recently published crystal structure of the Band 3 membrane domain. © 2017 IUBMB Life, 70(1):32-40, 2018.

SLC4A11 Three-Dimensional Homology Model Rationalizes Corneal Dystrophy-Causing Mutations.

We studied the structural effects of point mutations of a membrane protein that cause genetic disease. SLC4A11 is a membrane transport protein (OH- /H+ /NH3 /H2 O) of basolateral corneal endothelium, whose mutations cause some cases of congenital hereditary endothelial dystrophy and Fuchs endothelial corneal dystrophy. We created a three-dimensional homology model of SLC4A11 membrane domain, using Band 3 (SLC4A1) crystal structure as template. The homology model was assessed in silico and by analysis of mutants designed on the basis of the model. Catalytic pathway mutants p.Glu675Gln, p.His724Arg, and p.His724Ala impaired SLC4A11 transport. p.Ala720Leu, in a region of extended structure of the proposed translocation pore, failed to mature to the cell surface. p.Gly509Lys, located in an open region at the core domain/gate domain interface, had wild-type level of transport function. The molecular phenotype of 37 corneal dystrophy-causing point mutants was rationalized, based on their location in the homology model. Four map to the substrate translocation pathway, 25 to regions of close transmembrane helix packing, three to the dimeric interface, and five lie in extramembraneous loops. The model provides a view of the spectrum of effects of disease mutations on membrane protein structure and provides a tool to analyze pathogenicity of additional newly discovered SLC4A11 mutants.