Rational Approach to Improve Detergent Efficacy for Membrane Protein Stabilization

Membrane protein structures are essential for the molecular understanding of diverse cellular processes and drug discovery. Detergents are not only widely used to extract membrane proteins from membranes but also utilized to preserve native protein structures in aqueous solution. However, micelles formed by conventional detergents are suboptimal for membrane protein stabilization, necessitating the development of novel amphiphilic molecules with enhanced protein stabilization efficacy. In this study, we prepared two sets of tandem malonate-derived glucoside (TMG) variants, both of which were designed to increase the alkyl chain density in micelle interiors. The alkyl chain density was modulated either by reducing the spacer length (TMG-Ms) or by introducing an additional alkyl chain between the two alkyl chains of the original TMGs (TMG-Ps). When evaluated with a few membrane proteins including a G protein-coupled receptor, TMG-P10,8 was found to be substantially more efficient at extracting membrane proteins and also effective at preserving protein integrity in the long term compared to the previously described TMG-A13. This result reveals that inserting an additional alkyl chain between the two existing alkyl chains is an effective way to optimize detergent properties for membrane protein study. This new biochemical tool and the design principle described have the potential to facilitate membrane protein structure determination.

Exploring the K+ binding site and its coupling to transport in the neurotransmitter:sodium symporter LeuT

The neurotransmitter:sodium symporters (NSSs) are secondary active transporters that couple the reuptake of substrate to the symport of one or two sodium ions. One bound Na+ (Na1) contributes to the substrate binding, while the other Na+ (Na2) is thought to be involved in the conformational transition of the NSS. Two NSS members, the serotonin transporter (SERT) and the Drosophila dopamine transporter (dDAT), also couple substrate uptake to the antiport of K+ by a largely undefined mechanism. We have previously shown that the bacterial NSS homologue, LeuT, also binds K+, and could therefore serve as a model protein for the exploration of K+ binding in NSS proteins. Here, we characterize the impact of K+ on substrate affinity and transport as well as on LeuT conformational equilibrium states. Both radioligand binding assays and transition metal ion FRET (tmFRET) yielded similar K+ affinities for LeuT. K+ binding was specific and saturable. LeuT reconstituted into proteoliposomes showed that intra-vesicular K+ dose-dependently increased the transport velocity of [3H]alanine, whereas extra-vesicular K+ had no apparent effect. K+ binding induced a LeuT conformation distinct from the Na+- and substrate-bound conformation. Conservative mutations of the Na1 site residues affected the binding of Na+ and K+ to different degrees. The Na1 site mutation N27Q caused a >10-fold decrease in K+ affinity but at the same time a ~3-fold increase in Na+ affinity. Together, the results suggest that K+ binding to LeuT modulates substrate transport and that the K+ affinity and selectivity for LeuT is sensitive to mutations in the Na1 site, pointing toward the Na1 site as a candidate site for facilitating the interaction with K+ in some NSSs.

Ethnic discrimination in Scandinavia: evidence from a field experiment in women's amateur soccer

In this paper, we examine ethnic discrimination using sport as a laboratory. Applying a field experiment in the three Scandinavian countries-Sweden, Norway, and Denmark-we test whether foreign female minority groups experience greater rejection rates when seeking inclusion in amateur soccer clubs. Soccer coaches were contacted by e-mail using native and foreign-sounding names from selected groups, requesting to participate in trial practice. Previous findings show persistent discrimination of foreign minority groups in the labour market, and recent work suggests that discrimination also occurs in the context of soccer. Our findings from Scandinavia show that Sweden is the only country that shows statistically significant signs of discriminatory patterns, and the probability of experiencing discrimination increases with cultural distance. However, cultural distance appears to have no influence in Norway and Denmark. We further investigate whether male or female coaches demonstrate different discriminatory behaviour when being contacted, but our analysis shows almost no gender differences. Findings suggest that how men and women differ in their discriminatory behaviour is context specific. The differences identified across nations and previous studies are discussed to better understand the mechanisms of discrimination.

Maltose-bis(hydroxymethyl)phenol (MBPs) and Maltose-tris(hydroxymethyl)phenol (MTPs) Amphiphiles for Membrane Protein Stability

Membrane protein structures provide a fundamental understanding of their molecular actions and are of importance for drug development. Detergents are widely used to solubilize, stabilize, and crystallize membrane proteins, but membrane proteins solubilized in conventional detergents are prone to denaturation and aggregation. Thus, developing novel detergents with enhanced efficacy for protein stabilization remains important. We report herein the design and synthesis of a class of phenol-derived maltoside detergents. Using two different linkers, we prepared two sets of new detergents, designated maltose-bis(hydroxymethyl)phenol (MBPs) and maltose-tris(hydroxymethyl)phenol (MTPs). The evaluation of these detergents with three transporters and two G-protein coupled receptors allowed us to identify a couple of new detergents (MBP-C9 and MTP-C12) that consistently conferred enhanced stability to all tested proteins compared to a gold standard detergent (DDM). Furthermore, the data analysis based on the detergent structures provides key detergent features responsible for membrane protein stabilization that together will facilitate the future design of novel detergents.

Complement C3d is not associated with axial spondyloarthritis and magnetic resonance imaging changes at the sacroiliac joint

Objective: To investigate the associations between complement C3d and inflammatory and structural changes by magnetic resonance imaging (MRI) at the sacroiliac joints (SIJ) suggestive of axial spondyloarthritis, according to the Assessment of SpondyloArthritis international Society (ASAS) criteria, in patients with low back pain.Method: This was a cross-sectional study of patients referred to the Spine Centre of Southern Denmark owing to unspecified low back pain (Spines of Southern Denmark cohort). The patients were divided into three groups: group 1: patients fulfilling the ASAS criteria for axial spondyloarthritis (axSpA, n = 96); group 2: patients with either a positive MRI of the SIJ and no spondyloarthritis features, or a negative MRI of the SIJ but positive human leucocyte antigen-B27 and one spondyloarthritis feature (non-axSpA, n = 38); group 3: patients with unspecified low back pain for > 3 months (control group, n = 82). Complement C3d was measured with double-decker rocket immunoelectrophoresis and evaluated in relation to the group division and baseline findings by SIJ MRI.Results: In total, 184 C3d analyses were performed. The mean ± sd level of C3d was 33.8 ± 8.1 AU/mL. There were no differences in C3d levels between the three patient groups, mean values being: axSpA = 34.3 ± 7.9 AU/mL, non-axSpA = 33.5 ± 6.9 AU/mL, and controls = 33.4 ± 9.2 AU/mL. The level of C3d was not related to MRI findings.Conclusions: In these patients, complement C3d was not associated with active or structural SIJ changes on MRI suggestive of axial spondyloarthritis.

New Malonate-Derived Tetraglucoside Detergents for Membrane Protein Stability

Membrane proteins are widely studied in detergent micelles, a membrane-mimetic system formed by amphiphilic compounds. However, classical detergents have serious limitations in their utility, particularly for unstable proteins such as eukaryotic membrane proteins and membrane protein complexes, and thus, there is an unmet need for novel amphiphiles with enhanced ability to stabilize membrane proteins. Here, we developed a new class of malonate-derived detergents with four glucosides, designated malonate-derived tetra-glucosides (MTGs), and compared these new detergents with previously reported octyl glucose neopentyl glycol (OGNG) and n-dodecyl-β-d-maltoside (DDM). When tested with two G-protein coupled receptors (GPCRs) and three transporters, a couple of MTGs consistently conferred enhanced stability to all tested proteins compared to DDM and OGNG. As a result of favorable behaviors for a range of membrane proteins, these MTGs have substantial potential for membrane protein research. This study additionally provides a new detergent design principle based on the effect of a polar functional group (i.e., ether) on protein stability depending on its position in the detergent scaffold.

The incidence of bone marrow oedema at the sacroiliac joints in a non-rheumatological population - a retrospective cohort study

Background

The purpose of this study is to determine the incidence of bone marrow oedema (BME) at magnetic resonance imaging (MRI) of the sacroiliac joints (SIJ) in a non- rheumatological population, and to explore whether patient-reported outcome measures are suitable for predicting BME at the SIJ at referral. Furthermore, to investigate the final clinical diagnoses three months after initial SIJ MRI.

Methods

This study was a retrospective cohort study consisting of patients 18–45 years of age that were referred for a SIJ MRI between 1 July 2016 to 30 June 2017 at the Department of Radiology in Lillebaelt Hospital, Denmark. The SIJ MRI radiological reports were evaluated for signs of BME. Principal and secondary diagnoses according to the 10th version of International Classification of Diseases (ICD-10)—three months after the initial MRI—were identified in the electronic patient record system. For a subgroup of patients, patient- reported outcome measures, such as the 23-item Roland Morris Disability Questionnaire, quality of life and pain intensity in the back and leg were included from the local SpineData database.

Results

In total, 333 patients were included, and 187 (56.2%) of those patients received a final diagnosis within three months after the SIJ MRI. BME was detected in 63 (18.9%) patients; 17 (9.1%) patients had both BME at SIJ MRI and were diagnosed with spondyloarthritis (M45/M46). There was no statistically significant difference between patients with and without BME regarding demographics, quality of life, pain descriptions or function.

Conclusions

The incidence of BME in the cohort correlates well to previous studies regarding the incidence of SIJ MRI changes in non-rheumatological populations in Denmark. Patient-reported outcome measures do not seem to contribute to identifying patients with early-phase BME in a non-rheumatological population.

Incidence of ankylosing spondylitis and spondyloarthritis in 2000-2013: a nationwide Danish cohort study

Objective: To describe the incidence of ankylosing spondylitis (AS) and spondyloarthritis (SpA) in the Danish population in 2000-2013, at national and regional level, and to investigate any trends in incidence over time.Methods: From the Danish National Patient Registry (NPR), we identified patients diagnosed with AS (International Classification of Diseases, 10th revision: M45) or SpA (M46) from 1 January 2000 to 31 December 2013. Patients without a relevant contact in NPR at 12-24 months after initial diagnosis were excluded. Incidence rate ratios (IRRs) were calculated using the background population of men and women aged 18-45 years in 2000-2013 as a comparator. Variations in incidence between periods and the five Danish regions were evaluated.Results: In total, 3042 incident cases were identified (AS: 1849; SpA: 1193). AS incidence increased from 476 in 2000-2004 to 660 in 2010-2013; the IRR (95% confidence interval) increased from 1.49 (1.33-1.67) in 2005-2009 to 1.74 (1.53-1.97) in 2010-2013. SpA incidence increased from 156 in 2000-2004 to 707 in 2010-2013; the IRR increased from 2.45 (2.03-2.94) in 2005-2009 to 6.31 (5.27-7.55) in 2010-2013. The incidence of both AS and SpA increased in all five regions.Conclusion: The incidence of both AS and SpA in Denmark increased from 2000 to 2013. However, the proportion of patients diagnosed with SpA rather than AS was significantly higher in 2010-2013. This may be due to increased awareness of SpA and new treatment options, but possibly also misclassification of patients with SpA.