Introducing protein deamidation: Landmark discoveries, societal outreach, and tentative priming workflow to address deamidation.

Our current knowledge on protein deamidation results from a journey that started almost 100 years ago, when a handful of researchers first described the non-enzymatic "desamidation" of glutamine, and the effect of different anions on the catalytic rate of the reaction. Since then, the field has tremendously expended and now finds outreach in very diverse areas. In light of all the recent articles published in these areas, it seemed timely to propose an integrated review on the subject, including a short historical overview of the landmark discoveries in the field, highlighting the current global positioning of protein deamidation in biology and non-biology fields, and concluding with a workflow for those asking if a protein can deamidate, and identify the residues involved. This review is essentially intended to provide newcomers in the field with an overview of how deamidation has penetrated our society and what tools are currently at hand to identify and quantify protein deamidation.

Missense variant c.1460 T > C (p.L487P) enhances protein degradation of ER mannosyltransferase ALG9 in two new ALG9-CDG patients presenting with West syndrome and review of the literature.

ALG9-CDG is a CDG-I defect within the group of Congenital Disorders of Glycosylation (CDG). We here describe the clinical symptoms of two new and unrelated ALG9-CDG patients, both carrying the novel homozygous missense variant c.1460 T > C (p.L487P) in the ALG9 gene which led to global developmental delay, psychomotor disability, facial dysmorphisms, brain and heart defects, hearing loss, hypotonia, as well as feeding problems. New clinical symptoms comprised West syndrome with hypsarrhythmia. Quantitative RT-PCR analysis revealed a significantly enhanced ALG9 mRNA transcript level, whereas the protein amount in fibroblasts was significantly reduced. This could be ascribed to a stronger degradation of the mutated ALG9 protein in patient fibroblasts. Lipid-linked oligosaccharide analysis showed an ALG9-CDG characteristic accumulation of Man6GlcNAc2-PP-dolichol and Man8GlcNAc2-PP-dolichol in patient cells. The clinical findings of our patients and of all previously published ALG9-CDG patients are brought together to further expand the knowledge about this rare N-glycosylation disorder. SYNOPSIS: Homozygosity for p.L487P in ALG9 causes protein degradation and leads to West syndrome.

SMAD6 variants in craniosynostosis: genotype and phenotype evaluation.

PURPOSE: Enrichment of heterozygous missense and truncating SMAD6 variants was previously reported in nonsyndromic sagittal and metopic synostosis, and interaction of SMAD6 variants with a common polymorphism nearBMP2 (rs1884302) was proposed to contribute to inconsistent penetrance. We determined the occurrence of SMAD6 variants in all types of craniosynostosis, evaluated the impact of different missense variants on SMAD6 function, and tested independently whether rs1884302 genotype significantly modifies the phenotype. METHODS: We performed resequencing of SMAD6 in 795 unsolved patients with any type of craniosynostosis and genotyped rs1884302 in SMAD6-positive individuals and relatives. We examined the inhibitory activity and stability of SMAD6 missense variants. RESULTS: We found 18 (2.3%) different rare damaging SMAD6 variants, with the highest prevalence in metopic synostosis (5.8%) and an 18.3-fold enrichment of loss-of-function variants comparedwith gnomAD data (P < 10-7). Combined with eight additional variants, ≥20/26 were transmitted from an unaffected parent but rs1884302 genotype did not predict phenotype. CONCLUSION: Pathogenic SMAD6 variants substantially increase the risk of both nonsyndromic and syndromic presentations of craniosynostosis, especially metopic synostosis. Functional analysis is important to evaluate missense variants. Genotyping of rs1884302 is not clinically useful. Mechanisms to explain the remarkable diversity of phenotypes associated with SMAD6 variants remain obscure.

Crim1C140S mutant mice reveal the importance of cysteine 140 in the internal region 1 of CRIM1 for its physiological functions.

Cysteine-rich transmembrane bone morphogenetic protein regulator 1 (CRIM1) is a type I transmembrane protein involved in the organogenesis of many tissues via its interactions with growth factors including BMP, TGF-ß, and VEGF. In this study, we used whole-exome sequencing and linkage analysis to identify a novel Crim1 mutant allele generated by ENU mutagenesis in mice. This allele is a missense mutation that causes a cysteine-to-serine substitution at position 140, and is referred to as Crim1C140S. In addition to the previously reported phenotypes in Crim1 mutants, Crim1C140S homozygous mice exhibited several novel phenotypes, including dwarfism, enlarged seminal vesicles, and rectal prolapse. In vitro analyses showed that Crim1C140S mutation affected the formation of CRIM1 complexes and decreased the amount of the overexpressed CRIM1 proteins in the cell culture supernatants. Cys140 is located in the internal region 1 (IR1) of the N-terminal extracellular region of CRIM1 and resides outside any identified functional domains. Inference of the domain architecture suggested that the Crim1C140S mutation disturbs an intramolecular disulfide bond in IR1, leading to the protein instability and the functional defects of CRIM1. Crim1C140S highlights the functional importance of the IR1, and Crim1C140S mice should serve as a valuable model for investigating the functions of CRIM1 that are unidentified as yet.

Characterization of SNPs in the dopamine-ß-hydroxylase gene providing new insights into its structure-function relationship.

Dopamine-ß-hydroxylase (DBH, EC 1.14.17.1), an oxido-reductase that catalyses the conversion of dopamine to norepinephrine, is largely expressed in sympathetic neurons and adrenal medulla. Several regulatory and structural variants in DBH associated with various neuropsychiatric, cardiovascular diseases and a few that may determine enzyme activity have also been identified. Due to paucity of studies on functional characterization of DBH variants, its structure-function relationship is poorly understood. The purpose of the study was to characterize five non-synonymous (ns) variants that were prioritized either based on previous association studies or Sorting Tolerant From Intolerant (SIFT) algorithm. The DBH ORF with wild type (WT) and site-directed mutagenized variants were transfected into HEK293 cells to generate transient and stable lines expressing these variant enzymes. Activity was determined by UPLC-PDA and corresponding quantity by MRMHR on a TripleTOF 5600 MS respectively of spent media from stable cell lines. Homospecific activity computed for the WT and variant proteins showed a marginal decrease in A318S, W544S and R549C variants. In transient cell lines, differential secretion was observed in the case of L317P, W544S and R549C. Secretory defect in L317P was confirmed by localization in ER. R549C exhibited both decreased homospecific activity and differential secretion. Of note, all the variants were seen to be destabilizing based on in silico folding analysis and molecular dynamics (MD) simulation, lending support to our experimental observations. These novel genotype-phenotype correlations in this gene of considerable pharmacological relevance have implications for dopamine-related disorders.

Production of human pro-relaxin H2 in the yeast Pichia pastoris.

BACKGROUND: Initially known as the reproductive hormone, relaxin was shown to possess other therapeutically useful properties that include extracellular matrix remodeling, anti-inflammatory, anti-ischemic and angiogenic effects. All these findings make relaxin a potential drug for diverse medical applications. Its precursor, pro-relaxin, is an 18 kDa protein, that shows activity in in vitro assays. Since extraction of relaxin from animal tissues raises several issues, prokaryotes and eukaryotes were both used as expression systems for recombinant relaxin production. Most productive results were obtained when using Escherichia coli as a host for human relaxin expression. However, in such host, relaxin precipitated in the form of inclusion bodies and, therefore, required several expensive recovery steps as cell lysis, refolding and reduction. RESULTS: To overcome the issues related to prokaryotic expression here we report the production and purification of secreted human pro-relaxin H2 by using the methylotrophic yeast Pichia pastoris as expression host. The methanol inducible promoter AOX1 was used to drive expression of the native and histidine tagged forms of pro-relaxin H2 in dual phase fed-batch experiments on the 22 L scale. Both protein forms presented the correct structure, as determined by mass spectrometry and western blotting analyses, and demonstrated to be biologically active in immune enzymatic assays. The presence of the tag allowed to simplify pro-relaxin purification obtaining higher purity. CONCLUSIONS: This work presents a strategy for microbial production of recombinant human pro-relaxin H2 in Pichia pastoris that allowed the obtainment of biologically active pro-hormone, with a final concentration in the fermentation broth ranging between 10 and 14 mg/L of product, as determined by densitometric analyses.

Predicting the pathogenicity of missense variants based on protein instability to support diagnosis of patients with novel variants of ARSL.

Rare diseases are estimated to affect 3.5%-5.9% of the population worldwide and are difficult to diagnose. Genome analysis is useful for diagnosis. However, since some variants, especially missense variants, are also difficult to interpret, tools to accurately predict the effect of missense variants are very important and needed. Here we developed a method, "VarMeter", to predict whether a missense variant is damaging based on Gibbs free energy and solvent-accessible surface area calculated from the AlphaFold 3D protein model. We applied this method to the whole-exome sequencing data of 900 individuals with rare or undiagnosed disease in our in-house database, and identified four who were hemizygous for missense variants of arylsulfatase L (ARSL; known as the genetic cause of chondrodysplasia punctata 1, CPDX1). Two individuals had a novel Ser89 to Asn (Ser89Asn) or Arg469 to Trp (Arg469Trp) substitution, respectively predicted as "damaging" or "benign"; the other two had an Arg111 to His (Arg111His) or Gly117 to Arg (Gly117Arg) substitution, respectively predicted as "damaging" or "possibly damaging" and previously reported in patients showing clinical manifestations of CDPX1. Expression and analysis of the missense variant proteins showed that the predicted pathogenic variants (Ser89Asn, Arg111His, and Gly117Arg) had complete loss of sulfatase activity and reduced protease resistance due to destabilization of protein structure, while the predicted benign variant (Arg469Trp) had activity and protease resistance comparable to those of wild-type ARSL. The individual with the novel pathogenic Ser89Asn variant exhibited characteristics of CDPX1, while the individual with the benign Arg469Trp variant exhibited no such characteristics. These findings demonstrate that VarMeter may be used to predict the deleteriousness of variants found in genome sequencing data and thereby support disease diagnosis.

Haploinsufficiency as a Foreground Pathomechanism of Poirer-Bienvenu Syndrome and Novel Insights Underlying the Phenotypic Continuum of CSNK2B-Associated Disorders.

CSNK2B encodes for the regulatory subunit of the casein kinase II, a serine/threonine kinase that is highly expressed in the brain and implicated in development, neuritogenesis, synaptic transmission and plasticity. De novo variants in this gene have been identified as the cause of the Poirier-Bienvenu Neurodevelopmental Syndrome (POBINDS) characterized by seizures and variably impaired intellectual development. More than sixty mutations have been described so far. However, data clarifying their functional impact and the possible pathomechanism are still scarce. Recently, a subset of CSNK2B missense variants affecting the Asp32 in the KEN box-like domain were proposed as the cause of a new intellectual disability-craniodigital syndrome (IDCS). In this study, we combined predictive functional and structural analysis and in vitro experiments to investigate the effect of two CSNK2B mutations, p.Leu39Arg and p.Met132LeufsTer110, identified by WES in two children with POBINDS. Our data prove that loss of the CK2beta protein, due to the instability of mutant CSNK2B mRNA and protein, resulting in a reduced amount of CK2 complex and affecting its kinase activity, may underlie the POBINDS phenotype. In addition, the deep reverse phenotyping of the patient carrying p.Leu39Arg, with an analysis of the available literature for individuals with either POBINDS or IDCS and a mutation in the KEN box-like motif, might suggest the existence of a continuous spectrum of CSNK2B-associated phenotypes rather than a sharp distinction between them.

A Minimally Invasive Approach for Preventing White Wine Protein Haze by Early Enzymatic Treatment.

Protein stability in bottled white wine is an essential organoleptic property considered by consumers. In this paper, the effectiveness of an early enzymatic treatment was investigated by adding a food-grade microbial protease at two different stages of winemaking: (i) at cold settling, for a short-term and low temperature (10 °C) action prior to alcoholic fermentation (AF); (ii) at yeast inoculum, for a long-lasting and medium temperature (18 °C) action during AF. The results reveal that protease sufficiently preserved its catalytic activity at both operational conditions: 10 °C (during cold settling) and 18 °C (during AF). Furthermore, protease addition (dosage 50-150 µL/L) raised the alcoholic fermentation rate. The treatment at yeast inoculum (dosage 50 µL/L) had a remarkable effect in preventing haze formation, as revealed by its impact on protein instability and haze-active proteins. This minimally invasive, time and resource-saving enzymatic treatment, integrated into the winemaking process, could produce stable white wine without affecting color quality and phenol content.

Turning Failures into Applications: The Problem of Protein ΔΔG Prediction.

After nearly two decades of research in the field of computational methods based on machine learning and knowledge-based potentials for ΔG and ΔΔG prediction upon variations, we now realize that all the approaches are poorly performing when tested on specific cases and that there is large space for improvement. Why this is so? Is it wrong the underlying assumption that experimental protein thermodynamics in solution reflects the thermodynamics of a single protein? Both machine learning and knowledge-based computational methods are rigorous and we know the solid theory behind. We are now in a critical situation, which suggests that predictions of protein instability upon variation should be considered with care. In the following, we will show how to cope with the problem of understanding which protein positions may be of interest for biotechnological and biomedical purposes. By applying a consensus procedure, we indicate possible strategies for the result interpretation.

The E262K mutation in Lamin A links nuclear proteostasis imbalance to laminopathy-associated premature aging.

Deleterious, mostly de novo, mutations in the lamin A (LMNA) gene cause spatio-functional nuclear abnormalities that result in several laminopathy-associated progeroid conditions. In this study, exome sequencing in a sixteen-year-old male with manifestations of premature aging led to the identification of a mutation, c.784G>A, in LMNA, resulting in a missense protein variant, p.Glu262Lys (E262K), that aggregates in nucleoplasm. While bioinformatic analyses reveal the instability and pathogenicity of LMNAE262K , local unfolding of the mutation-harboring helical region drives the structural collapse of LMNAE262K into aggregates. The E262K mutation also disrupts SUMOylation of lysine residues by preventing UBE2I binding to LMNAE262K , thereby reducing LMNAE262K degradation, aggregated LMNAE262K sequesters nuclear chaperones, proteasomal proteins, and DNA repair proteins. Consequently, aggregates of LMNAE262K disrupt nuclear proteostasis and DNA repair response. Thus, we report a structure-function association of mutant LMNAE262K with toxicity, which is consistent with the concept that loss of nuclear proteostasis causes early aging in laminopathies.

The Instability of Dimeric Fc-Fusions Expressed in Plants Can Be Solved by Monomeric Fc Technology.

The potential therapeutic value of many proteins is ultimately limited by their rapid in vivo clearance. One strategy to limit clearance by metabolism and excretion, and improving the stability of therapeutic proteins, is their fusion to the immunoglobulin fragment crystallizable region (Fc). The Fc region plays multiple roles in (i) dimerization for the formation of "Y"-shaped structure of Ig, (ii) Fc-mediated effector functions, (iii) extension of serum half-life, and (iv) a cost-effective purification tag. Plants and in particular Nicotiana benthamiana have proven to be suitable expression platforms for several recombinant therapeutic proteins. Despite the enormous success of their use for the production of full-length monoclonal antibodies, the expression of Fc-fused therapeutic proteins in plants has shown limitations. Many Fc-fusion proteins expressed in plants show different degrees of instability resulting in high amounts of Fc-derived degradation products. To address this issue, we used erythropoietin (EPO) as a reporter protein and evaluated the efforts to enhance the expression of full-length EPO-Fc targeted to the apoplast of N. benthamiana. Our results show that the instability of the fusion protein is independent from the Fc origin or IgG subclass and from the peptide sequence used to link the two domains. We also show that a similar instability occurs upon the expression of individual heavy chains of monoclonal antibodies and ScFv-Fc that mimic the "Y"-shape of antibodies but lack the light chain. We propose that in this configuration, steric hindrance between the protein domains leads to physical instability. Indeed, mutations of critical residues located on the Fc dimerization interface allowed the expression of fully stable EPO monomeric Fc-fusion proteins. We discuss the limitations of Fc-fusion technology in N. benthamiana transient expression systems and suggest strategies to optimize the Fc-based scaffolds on their folding and aggregation resistance in order to improve the stability.

Protein stability in pulmonary drug delivery via nebulization.

Protein inhalation is a delivery route which offers high potential for direct local lung application of proteins. Liquid formulations are usually available in early stages of biopharmaceutical development and nebulizers are the device of choice for atomization avoiding additional process steps like drying and enabling fast progression to clinical trials. While some proteins were proven to remain stable throughout aerosolization e.g. DNase, many biopharmaceuticals are more susceptible towards the stresses encountered during nebulization. The main reason for protein instability is unfolding and aggregation at the air-liquid interface, a problem which is of particular challenge in the case of ultrasound and jet nebulizers due to recirculation of much of the generated droplets. Surfactants are an important formulation component to protect the sensitive biomolecules. A second important challenge is warming of ultrasound and vibrating mesh devices, which can be overcome by overfilling, precooled solutions or cooling of the reservoir. Ultimately, formulation development has to go hand in hand with device evaluation.

Influence of the structural features of commercial mannoproteins in white wine protein stabilization and chemical and sensory properties.

The cloudy aspect formed in white wines due to protein instability is a visual defect. Sodium bentonite is the most commonly used fining agent to treat this instability, but has usually a negative impact on the wine's physicochemical and sensory characteristics. Aiming to find suitable alternatives, eleven commercial mannoproteins were chemically characterized concerning their sugar composition and protein content, and their effectiveness on wine protein stabilization. Also, their effect on the amount and nature of phenolic compounds, browning potential, chromatic and sensory characteristic was evaluated. Protein stabilization effectiveness was related to their chemical composition, namely their high mannose to glucose ratio. Additionally, some mannoproteins decreased the browning potential. Thus, mannoproteins could be an effective alternative for protein stabilization, preserving or even improving wine quality.

Influenza evolution navigates stability valleys.

By reconstructing how an influenza protein collected in 1968 might have evolved into one collected in 2007, researchers have obtained new insights into the interactions between genetic mutations.