Reconstitution of 3' end processing of mammalian pre-mRNA reveals a central role of RBBP6.

The 3' ends of almost all eukaryotic mRNAs are generated in an essential two-step processing reaction: endonucleolytic cleavage of an extended precursor followed by the addition of a poly(A) tail. By reconstituting the reaction from overproduced and purified proteins, we provide a minimal list of 14 polypeptides that are essential and two that are stimulatory for RNA processing. In a reaction depending on the polyadenylation signal AAUAAA, the reconstituted system cleaves pre-mRNA at a single preferred site corresponding to the one used in vivo. Among the proteins, cleavage factor I stimulates cleavage but is not essential, consistent with its prominent role in alternative polyadenylation. RBBP6 is required, with structural data showing it to contact and presumably activate the endonuclease CPSF73 through its DWNN domain. The C-terminal domain of RNA polymerase II is dispensable. ATP, but not its hydrolysis, supports RNA cleavage by binding to the hClp1 subunit of cleavage factor II with submicromolar affinity.

Y(III) Sorption at the Orthoclase (001) Surface Measured by X-ray Reflectivity.

Interactions of heavy metals with charged mineral surfaces control their mobility in the environment. Here, we investigate the adsorption of Y(III) onto the orthoclase (001) basal plane, the former as a representative of rare earth elements and an analogue of trivalent actinides and the latter as a representative of naturally abundant K-feldspar minerals. We apply in situ high-resolution X-ray reflectivity to determine the sorption capacity and molecular distribution of adsorbed Y species as a function of the Y3+ concentration, [Y3+], at pH 7 and 5. With [Y3+] ≥ 1 mM at pH 7, we observe an inner-sphere (IS) sorption complex at a distance of ∼1.5 Å from the surface and an outer-sphere (OS) complex at 3-4 Å. Based on the adsorption height of the IS complex, a bidentate, binuclear binding mode, in which Y3+ binds to two terminal oxygens, is proposed. In contrast, mostly OS sorption is observed at pH 5. The observed maximum Y coverage is ∼1.3 Y3+/AUC (AUC: area of the unit cell = 111.4 Å2) for all the investigated pH values and Y concentrations, which is in the expected range based on the estimated surface charge of orthoclase (001).

MOFs with 12-Coordinate 5f-Block Metal Centers.

We have constructed an unprecedented MOF platform that accommodates a range of 5f-block metal ions (Th4+, U4+, Np4+, Pu4+) as the primary building block. The isoreticular actinide metal-organic frameworks (An-MOFs) exhibit periodic trends in the 12-coordinate metal environment, ligand configuration, and resulting ultramicroporosity. It holds potential in distinguishing neighboring tetravalent actinides. The metal ionic radius, carboxylate bite angle, anthracene plane twisting, interligand interactions, and countercation templating collectively determine an interplay between solvation, modulation, and complexation, resulting in a coordination saturation of the central actinide, while lanthanide counterparts are stabilized by the formation of a dimer-based motif. Quantum chemical calculations indicate that this large coordination number is only feasible in the high-symmetry environment provided by the An-MOFs. This category of MOFs not only demonstrates autoluminescence (4.16 × 104 counts per second per gram) but also portends a wide-bandgap (2.84 eV) semiconducting property with implications for a multitude of applications such as hard radiation detection.

Insights into the Electronic Structure of a U(IV) Amido and U(V) Imido Complex.

Reaction of the N-heterocylic carbene ligand i PrIm (L1 ) and lithium bis(trimethylsilyl)amide (TMSA) as a base with UCl4 resulted in U(IV) and U(V) complexes. Uranium's +V oxidation state in (HL1 )2 [U(V)(TMSI)Cl5 ] (TMSI=trimethylsilylimido) (2) was confirmed by HERFD-XANES measurements. Solid state characterization by SC-XRD and geometry optimisation of [U(IV)(L1 )2 (TMSA)Cl3 ] (1) indicated a silylamido ligand mediated inverse trans influence (ITI). The ITI was examined regarding different metal oxidation states and was compared to transition metal analogues by theoretical calculations.

Structural analysis of random transgene integration in CHO manufacturing cell lines by targeted sequencing.

Genetically modified CHO cell lines are traditionally used for the production of biopharmaceuticals. However, an in-depth molecular understanding of the mechanism and exact position of transgene integration into the genome of pharmaceutical manufacturing cell lines is still scarce. Next-generation sequencing (NGS) holds great promise for strongly facilitating the understanding of CHO cell factories, as it has matured to a powerful and affordable technology for cellular genotype analysis. Targeted Locus Amplification (TLA) combined with NGS allows for robust detection of genomic positions of transgene integration and structural genomic changes occurring upon stable integration of expression vectors. TLA was applied to generate comparative genomic fingerprints of several CHO production cell lines expressing different monoclonal antibodies. Moreover, high producers resulting from an additional round of transfection of an existing cell line (supertransfection) were analyzed to investigate the integrity and the number of integration sites. Our analyses enabled detailed genetic characterization of the integration regions with respect to the number of integrates and structural changes of the host cell's genome. Single integration sites per clone with concatenated transgene copies could be detected and were in some cases found to be associated with genomic rearrangements, deletions or translocations. Supertransfection resulted in an increase in titer associated with an additional integration site per clone. Based on the TLA fingerprints, CHO cell lines originating from the same mother clone could clearly be distinguished. Interestingly, two CHO cell lines originating from the same mother clone were shown to differ genetically and phenotypically despite their identical TLA fingerprints. Taken together, TLA provides an accurate genetic characterization with respect to transgene integration sites compared with conventional methods and represents a valuable tool for a comprehensive evaluation of CHO production clones early in cell line development.

Comparative Analysis of Mononuclear 1:1 and 2:1 Tetravalent Actinide (U, Th, Np) Complexes: Crystal Structure, Spectroscopy, and Electrochemistry.

Six mononuclear tetravalent actinide complexes (1-6) have been synthesized using a new Schiff base ligand 2-methoxy-6-(((2-methyl-1-(pyridin-2-yl)propyl)imino)methyl)phenol (HLpr). The HLpr is treated with tetravalent actinide elements in varied stoichiometries to afford mononuclear 1:1 complexes [MCl3-Lpr·nTHF] (1-3) and 2:1 complexes [MCl2-L2pr] (4-6) (M = Th4+ (1 and 4), U4+ (2 and 5), and Np4+ (3 and 6)). All complexes are characterized using different analytical techniques such as IR, NMR, and absorption spectroscopy as well as crystallography. UV-vis spectroscopy revealed more red-shifted absorption spectra for 2:1 complexes as compared to 1:1 complexes. 1H NMR of Th(IV) complexes exhibit diamagnetic spectra, whereas U(IV) and Np(IV) complexes revealed paramagnetically shifted 1H NMR. Interestingly, NMR signals are paramagnetically shifted between -70 and 40 ppm in 2 and 3 but are confined within -35 to 25 ppm in 2:1 complexes 5 and 6. Single-crystal structures for 1:1 complexes revealed an eight-coordinated Th(IV) complex (1) and seven-coordinated U(IV) (2) and Np(IV) (3) complexes. However, all 2:1 complexes 4-6 were isolated as eight-coordinated isostructural molecules. The geometry around the Th4+ center in 1 is found to be trigonal dodecahedral and capped trigonal prismatic around U(IV) and Np(IV) centers in 2 and 3, respectively. However, An4+ centers in 2:1 complexes are present in dodecahedral geometry. Importantly, 2:1 complexes exhibit increased bond distances in comparison to their 1:1 counterparts as well as interesting bond modulation with respect to ionic radii of An(IV) centers. Cyclic voltammetry displays an increased oxidation potential of the ligand by 300-500 mV, after coordination with An4+. CV studies indicate Th(IV)/Th(II) reduction beyond -2.3 V, whereas attempts were made to identify redox potentials for U(IV) and Np(IV) centers. Spectroscopic binding studies reveal that complex stability in 1:1 stoichiometry follows the order Th4+ ≈ U4+ > Np4+.

ROBL-II at ESRF: a synchrotron toolbox for actinide research.

ROBL-II provides four different experimental stations to investigate actinide and other alpha- and beta-emitting radionuclides at the new EBS storage ring of ESRF within an energy range of 3 to 35 keV. The XAFS station consists of a highly automatized, high sample throughput installation in a glovebox, to measure EXAFS and conventional XANES of samples routinely at temperatures down to 10 K, and with a detection limit in the sub-p.p.m. range. The XES station with its five bent-crystal analyzer, Johann-type setup with Rowland circles of 1.0 and 0.5 m radii provides high-energy resolution fluorescence detection (HERFD) for XANES, XES, and RIXS measurements, covering both actinide L and M edges together with other elements accessible in the 3 to 20 keV energy range. The six-circle heavy duty goniometer of XRD-1 is equipped for both high-resolution powder diffraction as well as surface-sensitive CTR and RAXR techniques. Single crystal diffraction, powder diffraction with high temporal resolution, as well as X-ray tomography experiments can be performed at a Pilatus 2M detector stage (XRD-2). Elaborate radioprotection features enable a safe and easy exchange of samples between the four different stations to allow the combination of several methods for an unprecedented level of information on radioactive samples for both fundamental and applied actinide and environmental research.

How 5 f Electron Polarisability Drives Covalency and Selectivity in Actinide N-Donor Complexes.

We report a series of isostructural tetravalent actinide (Th, U-Pu) complexes with the N-donor ligand N,N'-ethylene-bis((pyrrole-2-yl)methanimine) (H2 L, H2 pyren). Structural data from SC-XRD analysis reveal [An(pyren)2 ] complexes with different An-Nimine versus An-Npyrrolide bond lengths. Quantum chemical calculations elucidated the bonding situation, including differences in the covalent character of the coordinative bonds. A comparison to the intensely studied analogous N,N'-ethylene-bis(salicylideneimine) (H2 salen)-based complexes [An(salen)2 ] displays, on average, almost equal electron sharing of pyren or salen with the AnIV , pointing to a potential ligand-cage-driven complex stabilisation. This is shown in the fixed ligand arrangement of pyren and salen in the respective AnIV complexes. The overall bond strength of the pure N-donor ligand pyren to AnIV (An=Th, U, Np, Pu) is slightly weaker than to salen, with the exception of the PaIV complex, which exhibits extraordinarily high electron sharing of pyren with PaIV . Such an altered ligand preference within the early AnIV series points to a specificity of the 5f1 configuration, which can be explained by polarisation effects of the 5 f electrons, allowing the strongest f electron backbonding from PaIV (5f1 ) to the N donors of pyren.

How 5 f Electron Polarisability Drives Covalency and Selectivity in Actinide N-Donor Complexes.

Invited for the cover of this issue is the group of Moritz Schmidt at the Helmholtz-Zentrum Dresden-Rossendorf. The image depicts the relative strength of bonds from an actinide to a pyrrole-based ligand in comparison with the salen ligand. Read the full text of the article at 10.1002/chem.202102849.

Comprehensive Bonding Analysis of Tetravalent f-Element Complexes of the Type [M(salen)2].

Key questions for the study of chemical bonding in actinide compounds are the degree of covalency that can be realized in the bonds to different donor atoms and the relative participation of 5f and 6d orbitals. A manifold of theoretical approaches is available to address these questions, but hitherto no comprehensive assessments are available. Here, we present an in-depth analysis of the metal-ligand bond in a series of actinide metal-organic compounds of the [M(salen)2] type (M = Ce, Th, Pa, U, Np, Pu) with the Schiff base N,N'-bis(salicylidene)ethylenediamine (salen). All compounds except the Pa complex (only included in the calculations) have been synthesized and characterized experimentally. The experimental data are then used as a basis to quantify the covalency of bonds to both N- and O-donor atoms using simple electron-density differences and the quantum theory of atoms in molecules (QTAIM) with interacting quantum atoms. In addition, the orbital origin of any covalent contributions was studied via natural population analysis (NPA). The results clearly show that the bond to the hard, charged O-donor atoms of salen is consistently not only stronger but also more covalent than bonds to the softer N-donor atoms. On the other hand, in a comparison of the metals, Th shows the most ionic bond character even compared to its 4f analogue Ce. A maximum of the covalency is found for Pa or Np by their absolute and relative covalent bond energies, respectively. This trend also correlates with a significant f- and d-orbital occupation for Pa and Np. These results underline that only a comprehensive computational approach is capable of fully characterizing the covalency in actinide complexes.

Structure and Thermodynamics of Eu(III) and Cm(III) Complexes with Glucuronic Acid.

Complexation by small organic ligands controls the bioavailability of contaminants and influences their mobility in the geosphere. We have studied the interactions of Cm3+, as a representative of the trivalent actinides, and Eu3+, as an inactive homologue, with glucuronic acid (GlcA) a simple sugar acid. Time-resolved laser-induced luminescence spectroscopy (TRLFS) shows that complexation at pH 5.0 occurs only at high ligand to metal ratios in the form of 1:1 complexes with standard formation constants log ß0 = 1.84 ± 0.22 for Eu3+ and log ß0 = 2.39 ± 0.19 for Cm3+. A combination of NMR, QMMM, and TRLFS reveals the structure of the complex to be a half-sandwich structure wherein the ligand binds through its carboxylic group, the ring oxygen, and a hydroxyl group in addition to five to six water molecules. Surprisingly, Y3+, which was used as a diamagnetic reference in NMR, prefers a different coordination geometry with bonding through at least two hydroxyl groups on the opposite side of a distorted GlcA molecule. QMMM simulations indicate that the differences in stability among Cm, Eu, and Y are related to ring strain induced by smaller cations. At higher pH a stronger complex was detected, most likely due to deprotonation of a coordinating OH group.

Heterogeneous Sorption of Radionuclides Predicted by Crystal Surface Nanoroughness.

Reactive transport modeling (RTM) is an essential tool for the prediction of contaminants' behavior in the bio- and geosphere. However, RTM of sorption reactions is constrained by the reactive surface site assessment. The reactive site density variability of the crystal surface nanotopography provides an "energetic landscape", responsible for heterogeneous sorption efficiency, not covered in current RTM approaches. Here, we study the spatially heterogeneous sorption behavior of Eu(III), as an analogue to trivalent actinides, on a polycrystalline nanotopographic calcite surface and quantify the sorption efficiency as a function of surface nanoroughness. Based on experimental data from micro-focus time-resolved laser-induced luminescence spectroscopy (µTRLFS), vertical scanning interferometry, and electron back-scattering diffraction (EBSD), we parameterize a surface complexation model (SCM) using surface nanotopography data. The validation of the quantitatively predicted spatial sorption heterogeneity suggests that retention reactions can be considerably influenced by nanotopographic surface features. Our study presents a way to implement heterogeneous surface reactivity into a SCM for enhanced prediction of radionuclide retention.

Molecular-Level Speciation of Eu(III) Adsorbed on a Migmatized Gneiss As Determined Using µTRLFS.

The interaction of Eu(III) with thin sections of migmatized gneiss from the Bukov Underground Research Facility (URF), Czech Republic, was characterized by microfocus time-resolved laser-induced luminescence spectroscopy (µTRLFS) with a spatial resolution of ∼20 µm, well below typical grain sizes of the material. By this approach, sorption processes can be characterized on the molecular level while maintaining the relationship of the speciation with mineralogy and topography. The sample mineralogy was characterized by powder X-ray diffraction and Raman microscopy, and the sorption was independently quantified by autoradiography using 152Eu. Representative µTRLFS studies over large areas of multiple mm2 reveal that sorption on the heterogeneous material is not dominated by any of the typical major constituent minerals (quartz, feldspar, and mica). Instead, minor phases such as chlorite and prehnite control the Eu(III) distribution, despite their low contribution to the overall composition of the material, as well as common but less studied phases like Mg-hornblende. In particular, prehnite shows high a sorption uptake as well as strong binding of Eu to the mineral surface. Sorption on prehnite and hornblende happens at the expense of feldspar, which showed the highest sorption uptake in a previous spatially resolved study on granitic rock. Similarly, sorption on quartz is reduced, even though only low quantities of strongly bound Eu(III) were found here previously. Our results illustrate how competition of mineral surfaces for adsorbing cations drives the metal distribution in heterogeneous systems.

Isoindoline-Based Nitroxides as Bioresistant Spin Labels for Protein Labeling through Cysteines and Alkyne-Bearing Noncanonical Amino Acids.

Electron paramagnetic resonance (EPR) spectroscopy in combination with site-directed spin labeling (SDSL) is a powerful tool in protein structural research. Nitroxides are highly suitable spin labeling reagents, but suffer from limited stability, particularly in the cellular environment. Herein we present the synthesis of a maleimide- and an azide-modified tetraethyl-shielded isoindoline-based nitroxide (M- and Az-TEIO) for labeling of cysteines or the noncanonical amino acid para-ethynyl-l-phenylalanine (pENF). We demonstrate the high stability of TEIO site-specifically attached to the protein thioredoxin (TRX) against reduction in prokaryotic and eukaryotic environments, and conduct double electron-electron resonance (DEER) measurements. We further generate a rotamer library for the new residue pENF-Az-TEIO that affords a distance distribution that is in agreement with the measured distribution.

Bonding Trends in Tetravalent Th-Pu Monosalen Complexes.

The synthesis of three complex series of the form [AnCl2 (salen)(Pyx)2 ] (H2 salen=N,N'-bis(salicylidene)ethylenediamine; Pyx=pyridine, 4-methylpyridine, 3,5-dimethylpyridine) with tetravalent early actinides (An=Th, U, Np, Pu) is reported with the goal to elucidate the affinity of these heavy elements for small neutral N-donor molecules. Structure determination by single-crystal XRD and characterization of bulk powders with infrared spectroscopy reveals isostructurality within each respective series and the same complex conformation in all reported structures. Although the trend of interatomic distances for An-Cl and An-N (imine nitrogen of salen or pyridyl nitrogen of Pyx) was found to reflect an ionic behavior, the trend of the An-O distances can only be described with additional covalent interactions for all elements heavier than thorium. All experimental results are supported by quantum chemical calculations, which confirm the mostly ionic character in the An-N and An-Cl bonds, as well as the highest degree of covalency of the An-O bonds. Structurally, the calculations indicate just minor electronic or steric effects of the additional Pyx substituents on the complex properties.

Series of Tetravalent Actinide Amidinates: Structure Determination and Bonding Analysis.

Two series of isostructural tetravalent actinide amidinates [AnX((S)-PEBA)3] (An = Th, U, Np; X = Cl, N3) bearing the chiral (S,S)-N,N'-bis(1-phenylethyl)benzamidinate ((S)-PEBA) ligand have been synthesized and thoroughly characterized in solid and in solution. This study expands the already reported tetravalent neptunium complexes to the lighter actinides thorium and uranium. Furthermore, a rare Ce(IV) amidinate [CeCl((S)-PEBA)3] was synthesized to compare its properties to those of the analogous tetravalent actinide complexes. All compounds were characterized in the solid state using single-crystal XRD and infrared spectroscopy and in solution using NMR spectroscopy. Quantum chemical bonding analysis including also the isostructural Pa and Pu complexes was used to characterize the covalent contributions to any bond involving the metal cation. Th shows the least covalent character throughout the series, even substantially smaller than for the Ce complex. For U, Np, and Pu, similar covalent bonding contributions are found, but a natural population analysis reveals different origins. The 6d participation is the highest for U and decreases afterward, whereas the 5f participation increases continuously from Pa to Pu.

Selective Adsorption of Pb(II) on an Annealed Hematite (1102) Surface: Evidence from Crystal Truncation Rod X-ray Diffraction and Density Functional Theory.

The Pb(II)-binding mechanism on an annealed hematite (1102) surface was studied using crystal truncation rod (CTR) X-ray diffraction coupled with density functional theory (DFT) calculations. The best fit CTR model suggested that Pb(II) sorbed selectively to one type of edge-sharing surface site (ES2) over two other potential surface sites. From the best fit model structure, it was found that the Pb surface complex species forms a trigonal pyramid geometry. The base consists of three oxygen groups, two of which are associated with the substrate surface (IO and IIIO) and one that is a distal O extending toward solution. The trigonal pyramid geometry is slightly distorted with Pb-O bond lengths ranging from 2.21 to 2.31 Å and O-Pb-O bond angles ranging from 72° to 75°. Under this structural distortion, the nearest distance between Pb and Fe is found to be 3.39(1) Å. Consistent with the CTR results, DFT calculations indicate the Pb binding energy at the ES2 site is at least 0.16 eV more favorable than that at the other two potential binding sites considered. Using bond-valence rules we propose a stoichiometry of Pb(II) binding on the hematite (1102) surface which indicates proton release through the deprotonation of all oxygen groups bonding to Pb.

Cm3+/Eu3+ induced structural, mechanistic and functional implications for calmodulin.

Trivalent actinides and their lanthanide homologues are being scrutinized for their potential health risk when ingested as a result of a range of industrial activities such as mining. Importantly, these ions are known to exhibit high affinity towards calmodulin (CaM). In case of their inadvertent uptake, the holoproteins that are occupied by these cations may block signal transduction pathways or increase the concentration of these ions in intact cells, which could lead to accumulation in human organs. Accordingly, this investigation employed spectroscopy, computational chemistry, calorimetry, and biochemistry to study the results of metal ion substitution on the protein structure, enzymatic activity and chemo- and cytotoxicity of An3+/Ln3+ ions. As will be demonstrated herein, our data confirm the higher affinity of Cm3+ and Eu3+ compared to Ca2+ to all 4 binding sites of CaM, with one site differing from the remaining three. This higher-affinity site will complex Eu3+ in an exothermic fashion; in contrast, ion binding to the three lower-affinity EF-hands was found to be endothermic. The overall endothermic binding process is ascribed to the loss of the hydration shells of the trivalent ions upon protein binding. These findings are supported by extensive quantum chemical calculations of full holo-CaM, which were performed at the MP2 level using the fragment molecular orbital method. The exceptional binding site (EF-hand 3) features fewer negatively charged residues compared to the other EF-hands, thereby allowing Eu3+ and Cm3+ to carry one or two additional waters compared to Ca2+-CaM, while also causing the structure of Cm3+/Eu3+-CaM to become slightly disordered. Moreover, the enzymatic activity decreases somewhat in comparison to Ca2+-CaM. By utilizing a combination of techniques, we were able to generate a comprehensive picture of the CaM-actinide/lanthanide system from the molecular level to its functional impact. Such knowledge could also be applied to other metal-binding proteins.

The novel deubiquitinase inhibitor b-AP15 induces direct and NK cell-mediated antitumor effects in human mantle cell lymphoma.

The first therapeutic proteasome inhibitor bortezomib has clinical efficacy in mantle cell lymphoma (MCL) which resulted in its incorporation in treatment algorithms for this disease. Impairment of proteasomal function by bortezomib is mediated via inhibition of the 20S core particle. However, proteasome function can also be modified by targeting upstream components of the ubiquitin-proteasome system. Recently, b-AP15 has been identified as a small molecule achieving proteasome inhibition by targeting the deubiquitinase (DUB) activity of the 19S regulatory subunit and was found to inhibit cancer cell growth in preclinical analyses. In the present study, both direct antitumor effects and the possibility to induce natural killer group 2 member D ligands (NKG2DL) to reinforce NK cell immunity with b-AP15 were investigated to provide a rational basis for clinical evaluation of this novel DUB inhibitor in MCL. Treatment with b-AP15 resulted in reduced viability as well as induction of apoptosis in a time- and dose-dependent manner, which could be attributed to caspase activation in MCL cells. In addition, treatment with b-AP15 differentially induced NKG2DL expression and subsequent NK cell lysis of MCL cells. These results indicate that the DUB inhibitor b-AP15 displays substantial antitumor activity in human MCL and suggest that b-AP15 might be a novel therapeutic option in the treatment of MCL that warrants clinical investigation.

Local Structural Effects of Eu3+ Incorporation into Xenotime-type Solid Solutions with Different Host Cations.

In this study, the effect of host cations on the local structure around the dopant site of materials from the xenotime family is systematically studied on the molecular level. A series of six Eu3+ -doped xenotime-type single crystals (Tb, Y, Ho, Er, Yb, and LuPO4 ) have been grown and spectroscopically analyzed by using polarization-dependent laser-induced luminescence spectroscopy (p-TRLFS). Our results demonstrate that the structural disorder changes in a non-linear manner with a structural break between Yb3+ and Lu3+ . Despite adopting identical crystal structures, the solid solutions of these materials vary significantly, and differ from monazite solid solutions. Similar Eu3+ incorporation behavior with a strongly distorted dopant site is found for the early members of the xenotime family, whereas LuPO4 with the largest host versus dopant radii mismatch is anomalous in that it contains the most symmetrical lattice site. This goes along with a significantly stronger crystal field, indicating a shorter Eu-O bond length, as well as a strong vibronic coupling to external translational lattice vibrations. The p-TRLFS analysis confirms the breakdown of the crystallographic site symmetry from D2d to C1 in YPO4 , whereas a small distortion of the crystallographic site in LuPO4 results in an S4 point symmetry for the Eu3+ cation. The lattice with the smallest cation host site is no longer sufficiently flexible to make room for Eu3+ and instead "forces" the guest ion to occupy a less distorted Lu3+ site.