CRAFTing Delivery of Membrane Proteins into Protocells using Nanodiscs.

For the successful generative engineering of functional artificial cells, a convenient and controllable means of delivering membrane proteins into membrane lipid bilayers is necessary. Here we report a delivery system that achieves this by employing membrane protein-carrying nanodiscs and the calcium-dependent fusion of phosphatidylserine lipid membranes. We show that lipid nanodiscs can fuse a transported lipid bilayer with the lipid bilayers of small unilamellar vesicles (SUVs) or giant unilamellar vesicles (GUVs) while avoiding recipient vesicles aggregation. This is triggered by a simple, transient increase in calcium concentration, which results in efficient and rapid fusion in a one-pot reaction. Furthermore, nanodiscs can be loaded with membrane proteins that can be delivered into target SUV or GUV membranes in a detergent-independent fashion while retaining their functionality. Nanodiscs have a proven ability to carry a wide range of membrane proteins, control their oligomeric state, and are highly adaptable. Given this, our approach may be the basis for the development of useful tools that will allow bespoke delivery of membrane proteins to protocells, equipping them with the cell-like ability to exchange material across outer/subcellular membranes.

A bacteriophage mimic of the bacterial nucleoid-associated protein Fis.

We report the identification and characterization of a bacteriophage λ-encoded protein, NinH. Sequence homology suggests similarity between NinH and Fis, a bacterial nucleoid-associated protein (NAP) involved in numerous DNA topology manipulations, including chromosome condensation, transcriptional regulation and phage site-specific recombination. We find that NinH functions as a homodimer and is able to bind and bend double-stranded DNA in vitro. Furthermore, NinH shows a preference for a 15 bp signature sequence related to the degenerate consensus favored by Fis. Structural studies reinforced the proposed similarity to Fis and supported the identification of residues involved in DNA binding which were demonstrated experimentally. Overexpression of NinH proved toxic and this correlated with its capacity to associate with DNA. NinH is the first example of a phage-encoded Fis-like NAP that likely influences phage excision-integration reactions or bacterial gene expression.

Conformational variability of goat ß-lactoglobulin: crystallographic and thermodynamic studies.

Goat ß-lactoglobulin (GLG), lipocalin protein sharing high sequence similarity to bovine ß-lactoglobulin (BLG), has been structurally and thermodynamically characterized. Two crystal forms of GLG have been obtained, trigonal (P3121) and orthorhombic (P21212), with unique molecular packing, not observed previously for BLG. In the trigonal structure, GLG molecules have EF-loop in closed conformation while in the orthorhombic structure, for the first time, symmetric and asymmetric dimers of ß-lactoglobulin are observed simultaneously. It indicates that the opening or closing EF-loop does not occur in both subunits at the same time but might be sequential and cooperative. Comparison of GLG and BLG structures revealed presence of various conformers of EF and GH. ITC studies showed that at pH 7.5 GLG binds sodium dodecyl sulfate with Gibbs energy similar to BLG, however, with different contribution from enthalpic and entropic component. At pH 7.5 GLG forms dimers with dimerization constant Ka = 34.28 × 10(3) M(-1), significantly higher than observed for BLG. Similar mechanism of conformational changes and ligand binding indicates that GLG and BLG may play analogous biological role.

Structure of two crystal forms of sheep ß-lactoglobulin with EF-loop in closed conformation.

Ovine ß-lactoglobulin has been isolated from whey fraction of sheep milk and crystallized. The high-resolution structures of two crystal forms (triclinic and trigonal) obtained at pH 7.0 have been determined revealing that ovine protein, similarly to its bovine analog, is dimeric. Access to the binding site located in the eight-stranded antiparallel ß-barrel in both structures is blocked by the EF loop that has been found in closed conformation. Similarly to bovine lactoglobulin (BLG), conformation of the EF loop is stabilized by hydrogen bond between Glu89 and Ser116 indicating that Tanford transition might occur with the same mechanism. The substitution at six positions in relation to the most abundant isoform B of BLG also affects the distribution of electrostatic potentials and the total charge.

The differences in binding 12-carbon aliphatic ligands by bovine ß-lactoglobulin isoform A and B studied by isothermal titration calorimetry and X-ray crystallography.

Isoforms A (LGB-A) and B (LGB-B) of bovine lactoglobulin, the milk protein, differ in positions 64 (D↔G) and 118 (V↔A). Interactions of LGB-A and LGB-B with sodium dodecyl sulfate (SDS), dodecyltrimethylammonium chloride (DTAC) and lauric acid (LA), 12-carbon ligands possessing differently charged polar groups, were investigated using isothermal titration calorimetry and X-ray crystallography, to study the proton linkage phenomenon and to distinguish between effects related to different isoforms and different ligand properties. The determined values of ΔS and ΔH revealed that for all ligands, binding is entropically driven. The contribution from enthalpy change is lower and shows strong dependence on type of buffer that indicates proton release from the protein varying with protein isoform and ligand type and involvement of LA and Asp64 (in isoform A) in this process. The ligand affinities for both isoforms were arranged in the same order, DTAC < LA < SDS, and were systematically lower for variant B. The entropy change of the complexation process was always higher for isoform A, but these values were compensated by changes in enthalpy, resulting in almost identical ΔG for complexes of both isoforms. The determined crystal structures showed that substitution in positions 64 and 118 did not influence the overall structure of LGB complexes. The chemical character of the ligand polar group did not affect the position of its aliphatic chain in protein ß-barrel, indicating a major role of hydrophobic interactions in ligand binding that prevailed even with the repulsion between positively charged DTAC and lysine residues located at binding site entrance.