The circularly permuted globin domain of androglobin exhibits atypical heme stabilization and nitric oxide interaction

In the decade since the discovery of androglobin, a multi-domain hemoglobin of metazoans associated with ciliogenesis and spermatogenesis, there has been little advance in the knowledge of the biochemical and structural properties of this unusual member of the hemoglobin superfamily. Using a method for aligning remote homologues, coupled with molecular modelling and molecular dynamics, we have identified a novel structural alignment to other hemoglobins. This has led to the first stable recombinant expression and characterization of the circularly permuted globin domain. Exceptional for eukaryotic globins is that a tyrosine takes the place of the highly conserved phenylalanine in the CD1 position, a critical point in stabilizing the heme. A disulfide bond, similar to that found in neuroglobin, forms a closed loop around the heme pocket, taking the place of androglobin's missing CD loop and further supporting the heme pocket structure. Highly unusual in the globin superfamily is that the heme iron binds nitric oxide as a five-coordinate complex similar to other heme proteins that have nitric oxide storage functions. With rapid autoxidation and high nitrite reductase activity, the globin appears to be more tailored toward nitric oxide homeostasis or buffering. The use of our multi-template profile alignment method to yield the first biochemical characterisation of the circularly permuted globin domain of androglobin expands our knowledge of the fundamental functioning of this elusive protein and provides a pathway to better define the link between the biochemical traits of androglobin with proposed physiological functions.

Exploring Ligand Binding to Calcitonin Gene-Related Peptide Receptors

Class B1 G protein-coupled receptors (GPCRs) are important targets for many diseases, including cancer, diabetes, and heart disease. All the approved drugs for this receptor family are peptides that mimic the endogenous activating hormones. An understanding of how agonists bind and activate class B1 GPCRs is fundamental for the development of therapeutic small molecules. We combined supervised molecular dynamics (SuMD) and classic molecular dynamics (cMD) simulations to study the binding of the calcitonin gene-related peptide (CGRP) to the CGRP receptor (CGRPR). We also evaluated the association and dissociation of the antagonist telcagepant from the extracellular domain (ECD) of CGRPR and the water network perturbation upon binding. This study, which represents the first example of dynamic docking of a class B1 GPCR peptide, delivers insights on several aspects of ligand binding to CGRPR, expanding understanding of the role of the ECD and the receptor-activity modifying protein 1 (RAMP1) on agonist selectivity.

Addressing free fatty acid receptor 1 (FFAR1) activation using supervised molecular dynamics

The free fatty acid receptor 1 (FFAR1, formerly GPR40), is a potential G protein-coupled receptor (GPCR) target for the treatment of type 2 diabetes mellitus (T2DM), as it enhances glucose-dependent insulin secretion upon activation by endogenous long-chain free fatty acids. The presence of two allosterically communicating binding sites and the lack of the conserved GPCR structural motifs challenge the general knowledge of its activation mechanism. To date, four X-ray crystal structures are available for computer-aided drug design. In this study, we employed molecular dynamics (MD) and supervised molecular dynamics (SuMD) to deliver insights into the (un)binding mechanism of the agonist MK-8666, and the allosteric communications between the two experimentally determined FFAR1 binding sites. We found that FFAR1 extracellular loop 2 (ECL2) mediates the binding of the partial agonist MK-8666. Moreover, simulations showed that the agonists MK-8666 and AP8 are reciprocally stabilized and that AP8 influences MK-8666 unbinding from FFAR1.

Deconvoluting the Molecular Control of Binding and Signaling at the Amylin 3 Receptor: RAMP3 Alters Signal Propagation through Extracellular Loops of the Calcitonin Receptor

Amylin is coexpressed with insulin in pancreatic islet β-cells and has potent effects on gastric emptying and food intake. The effect of amylin on satiation has been postulated to involve AMY3 receptors (AMY3R) that are heteromers of the calcitonin receptor (CTR) and receptor activity-modifying protein 3 (RAMP3). Understanding the molecular control of signaling through the AMY3R is thus important for peptide drug targeting of this receptor. We have previously used alanine scanning mutagenesis to study the contribution of the extracellular surface of the CTR to binding and signaling initiated by calcitonin (CT) and related peptides (Dal Maso, E., et al. (2019) The molecular control of calcitonin receptor signaling. ACS Pharmacol. Transl. Sci. 2, 31-51). That work revealed ligand- and pathway-specific effects of mutation, with extracellular loops (ECLs) 2 and 3 particularly important in the distinct propagation of signaling mediated by individual peptides. In the current study, we have used equivalent alanine scanning of ECL2 and ECL3 of the CTR in the context of coexpression with RAMP3 to form AMY3Rs, to examine functional affinity and efficacy of peptides in cAMP accumulation and extracellular signal-regulated kinase (ERK) phosphorylation (pERK). The effect of mutation was determined on representatives of the three major distinct classes of CT peptide, salmon CT (sCT), human CT (hCT), and porcine CT (pCT), as well as rat amylin (rAmy) or human α-CGRP (calcitonin gene-related peptide, hCGRP) whose potency is enhanced by RAMP interaction. We demonstrate that the dynamic nature of CTR ECL2 and ECL3 in propagation of signaling is fundamentally altered when complexed with RAMP3 to form the AMY3R, despite only having predicted direct interactions with ECL2. Moreover, the work shows that the role of these loops in receptor signaling is highly peptide dependent, illustrating that even subtle changes to peptide sequence may change signaling output downstream of the receptor.

The Molecular Control of Calcitonin Receptor Signaling

The calcitonin receptor (CTR) is a class B G protein-coupled receptor (GPCR) that responds to the peptide hormone calcitonin (CT). CTs are clinically approved for the treatment of bone diseases. We previously reported a 4.1 Å structure of the activated CTR bound to salmon CT (sCT) and heterotrimeric Gs protein by cryo-electron microscopy (Liang, Y.-L., et al. Phase-plate cryo- EM structure of a class B GPCR-G protein complex. Nature 2017, 546, 118-123). In the current study, we have reprocessed the electron micrographs to yield a 3.3 Å map of the complex. This has allowed us to model extracellular loops (ECLs) 2 and 3, and the peptide N-terminus that previously could not be resolved. We have also performed alanine scanning mutagenesis of ECL1 and the upper segment of transmembrane helix 1 (TM1) and its extension into the receptor extracellular domain (TM1 stalk), with effects on peptide binding and function assessed by cAMP accumulation and ERK1/2 phosphorylation. These data were combined with previously published alanine scanning mutagenesis of ECL2 and ECL3 and the new structural information to provide a comprehensive 3D map of the molecular surface of the CTR that controls binding and signaling of distinct CT and related peptides. The work highlights distinctions in how different, related, class B receptors may be activated. The new mutational data on the TM1 stalk and ECL1 have also provided critical insights into the divergent control of cAMP versus pERK signaling and, collectively with previous mutagenesis data, offer evidence that the conformations linked to these different signaling pathways are, in many ways, mutually exclusive. This study furthers our understanding of the complex nature of signaling elicited by GPCRs and, in particular, that of the therapeutically important class B subfamily.

Traditional cardiovascular risk factors or inflammation: Which factors accelerate atherosclerosis in arthritis patients?

Patients with chronic inflammatory arthritis experience an increased incidence of cardiovascular (CV) events. In addition to visualizing atherosclerotic plaques, ultrasound examinations (USs) of the carotid arteries permit the measurement of subclinical markers of atherosclerosis, such as intima-media thickness (cIMT) and carotid segmental distensibility (cDC). The aims of the study were to identify the determinants of atherosclerosis acceleration (plaques, cIMT and cDC) in a sample of patients suffering from chronic arthritis and to compare these patients with a control group of people with ≤1 traditional risk factor (TRF) for CV disease.

METHODS

We recruited 137 patients with rheumatoid arthritis (RA), 43 patients with psoriatic arthritis (PsA), 28 patients with ankylosing spondylitis (AS) and 48 healthy volunteers without histories of previous CV events. These patients underwent carotid artery US examinations using dedicated hardware.

RESULTS

Regression and multivariate analyses demonstrated that only age (p<0.001) was consistently associated with cDC, cIMT and atherosclerotic plaques, both in the entire sample of patients with arthritis and in the subgroup of patients with RA. Among modifiable TRFs for cardiovascular disease, only hypertension, diabetes mellitus and smoking exhibited associations with some carotid phenotypes, with borderline significance. When patients with RA carrying ≤1 TRF were compared with control subjects carrying ≤1 TRF, only cDC was slightly lower in the RA group than in the control group.

CONCLUSIONS

Age is the major determinant of subclinical atherosclerosis in patients with different types of arthritis, as the contributions of other TRFs and disease activity and duration indices to the disease seem to be limited.

Review of rehabilitation and orthopedic conservative approach to sagittal plane diseases during growth: hyperkyphosis, junctional kyphosis, and Scheuermann disease

An increase of the physiological kyphosis during growth is defined hyperkyphosis (HK) and, according to the level where the apex of the curve can be retrieved, we can distinguish a thoracic HK and a thoraco-lumbar one, also called junctional kyphosis. Since these conditions can cause pain and esthetics impairments, lead in adulthood to an higher incidence of spinal and shoulder pain, and evolve during growth, it is important to manage this deformity. The aim of this paper was to present the state of the art about HK and its treatment. Scheuermann Disease (SCHK) is the better known cause of HK; other causes can be idiopathic or postural, trunk extensor muscles weakness or neurological problems. Despite etiology a specific treatment can be required during growth to prevent evolution and reach a better spinal alignment in adulthood. It is at the base of treatment and allow monitoring. There are some validated methods that can be used in a comprehensive rehabilitation approach. Evidence in this field is scanty, even if there is quite a consensus on possible treatments. They aim at improving posture and esthetics, and abolishing pain; they include: exercises, used mainly in mobile postural/idiopathic HK, and in SCHK without HK; braces (plus exercises, in this case aimed at reducing brace impairments), that in rigid HK and in most of SCHK patients also allow a better vertebral growth; surgery could be used in worst cases, even if it should be carefully considered, because it requires fusion and loss of spinal function.

Rehabilitation of adolescent idiopathic scoliosis: results of exercises and bracing from a series of clinical studies. Europa Medicophysica-SIMFER 2007 Award Winner

AIM

Rehabilitation of adolescent idiopathic scoliosis (AIS) requires a careful choice from among the possible treatments, such as bracing and exercises, according to the patient's needs. According to the literature, there is little evidence regarding the efficacy of these rehabilitation instruments. During the past few years, a full series of studies has been carried out to investigate their efficacy. The aim of this paper was to summarize all these results.

METHODS

Three systematic reviews (two on exercises and one on manual therapy), and four cohort prospective studies were performed. The prospective studies included two trials with a prospective control group on exercises (one to avoid bracing and one in preparation to bracing) and two trials with retrospective control group on a new brace developed by the Authors (Sforzesco brace and SPoRT concept of correction versus Lyon brace and Risser cast).

RESULTS

Results show that in literature there is proof of level 1b on exercises but no studies on manual therapy. High quality exercises like Scientific Exercises Approach to Scoliosis (SEAS) have more efficacy than usual physiotherapy, significantly reducing brace prescription in one year from 25% of cases to 6%. Moreover, such exercises help to obtain the best results in bracing first correction. The Sforzesco brace has proved to have more efficacy than the Lyon brace, whereas it has the same efficacy--but reduced side effects and impact on quality of life--than the Risser brace.

CONCLUSION

With an efficient management of data collection, it is possible to develop a set of studies aimed at verifying the efficacy of clinical daily rehabilitation approaches.

Clinical and postural behaviour of scoliosis during daily brace weaning hours

What happens to scoliosis when the brace is daily weaned is not described in the literature, even if this can have a significant clinical impact. Our aim was to evaluate the postural and clinical changes at brace weaning. We developed a pre-post trial in 10 adolescent idiopathic scoliosis female patients 12.6 years old, with 42.8+/-7.4 degrees Cobb curves.

INCLUSION CRITERIA

more than 30 degrees Cobb; TLSO worn at least 20 hours/day. Patients have been divided according to the hours of brace wearing per day: group 23H (6 patients, 23 hours per day) and group 20H (20-21 hours per day). We evaluated the patients at brace weaning and every hour per 4 hours, clinically (Bunnell degrees, hump and plumbline distances through usual clinical instruments) and posturally (scoliosis degree), by means of a non-ionising instrument that allow a 3D reconstruction of the spine. Paired ANOVA and t-test were used for statistical analysis. Group 23H showed statistically significant variations in 1 to 3 hours in all clinical parameters, and a tendency to progression of scoliosis. Group 20H did not show any statistically significant variation in 4 hours, a part from slight improvements. These results could be explained in terms of scoliosis reactions to usual/unusual daily load on the spine. Moreover, these data show the possible existence of the "concertina effect" due to brace weaning, and the importance of standardizing clinical examination with respect to the daily brace weaning hours.

BRACE MAP, a proposal for a new classification of braces

Braces today are named according to the author's name or town. The existing classification of braces considers only the anatomical spinal section involved (C: cervical; T: thoracic; L: lumbar; S: sacral; Orthosis). The absence of a more detailed classification do not allow to really distinguish between the different braces and to have a common language between the conservative treatment experts. Our aim was to propose and verify a new classification of braces. We developed the classification and applied it to 13 different braces (Boston, Charleston, Cheneau 2000, Lapadula, Lyonese, Maguelone, Milwaukee, PASB, Providence, Sforzesco, Sibilla, SpineCor, Triac). We considered the following items (acronym BRACE MAP): Building, Rigidity, Anatomical classification, Construction of the Envelope, Mechanism of Action, Plane of action. Each item is composed by 2 to 7 classificatory elements defined using one or maximum two letters, so that from the classification it is possible to come back to the brace characteristics. Out of the 13 braces considered, BRACE MAP did not allow to differentiate only two. This first proposal needs to be refined through Consensus and discussions that are already underway in the international Society On Scoliosis Orthopaedic and Rehabilitation Treatment (SOSORT); nevertheless, BRACE MAP appears to be useful in distinguishing between the existing braces.

Do imbalance situations stimulate a spinal straightening reflex in patient with adolescent idiopathic scoliosis?

Correlation between balance and Adolescent Idiopathic Scoliosis (AIS) is still unclear. To identify the most useful type of physical exercises to be proposed for conservative treatment, is interesting to explore better this field. Our aim was to evaluate the changes of scoliosis curves in a group AIS patients while submitted to an unbalancing situation. We considered in a pre-post trial 14 AIS patients (46 curves), 12 to 15 years old, with 19.3+/-9.9 degrees Cobb curves. Assessment has been made using GOALS (Global Optoelectronic Approach for Locomotion and Spine), a non-ionising instrument that allow a 3D reconstruction of the spine. We evaluated the patients twice in a standardised standing position: on the floor, and on a sway bench. On the sway bench there was a statistically (but not clinically) significant reduction of the curves. This was confirmed considering the average of the curves of each patient, but not when considering the worst curve. Looking at the curves, 13% worsened and 33% improved, versus 14% and 43% respectively looking at the patients. We did not find similar reactions in all patients, but in general a spinal straightening reflex while on a sway bench appears. In any case these variations are of low degree.