Comprehensive Peptide Cyclization Examination Yields Optimized APP Scaffolds with Improved Affinity toward Mint2.

Peptides targeting disease-relevant protein-protein interactions are an attractive class of therapeutics covering the otherwise undruggable space between small molecules and therapeutic proteins. However, peptides generally suffer from poor metabolic stability and low membrane permeability. Hence, peptide cyclization has become a valuable approach to develop linear peptide motifs into metabolically stable and potentially cell-permeable cyclic leads. Furthermore, cyclization of side chains, also known as "stapling", can stabilize particular secondary peptide structures. Here, we demonstrate that a comprehensive examination of cyclization strategies in terms of position, chemistry, and length is a prerequisite for the selection of optimal cyclic peptide scaffolds. Our systematic approach identifies cyclic APP dodecamer peptides targeting the phosphotyrosine binding domain of Mint2 with substantially improved affinity. We show that especially all-hydrocarbon stapling provides improved metabolic stability, a significantly stabilized secondary structure and membrane permeability.

Molecular Details of a Coupled Binding and Folding Reaction between the Amyloid Precursor Protein and a Folded Domain.

Intrinsically disordered regions in proteins often function as binding motifs in protein-protein interactions. The mechanistic aspects and molecular details of such coupled binding and folding reactions, which involve formation of multiple noncovalent bonds, have been broadly studied theoretically, but experimental data are scarce. Here, using a combination of protein semisynthesis to incorporate phosphorylated amino acids, backbone amide-to-ester modifications, side chain substitutions, and binding kinetics, we examined the interaction between the intrinsically disordered motif of amyloid precursor protein (APP) and the phosphotyrosine binding (PTB) domain of Mint2. We show that the interaction is regulated by a self-inhibitory segment of the PTB domain previously termed ARM. The helical ARM linker decreases the association rate constant 30-fold through a fast pre-equilibrium between an open and a closed state. Extensive side chain substitutions combined with kinetic experiments demonstrate that the rate-limiting transition state for the binding reaction is governed by native and non-native hydrophobic interactions and hydrogen bonds. Hydrophobic interactions were found to be particularly important during crossing of the transition state barrier. Furthermore, linear free energy relationships show that the overall coupled binding and folding reaction involves cooperative formation of interactions with roughly 30% native contacts formed at the transition state. Our data support an emerging picture of coupled binding and folding reactions following overall chemical principles similar to those of folding of globular protein domains but with greater malleability of ground and transition states.

Targeting the APP-Mint2 Protein-Protein Interaction with a Peptide-Based Inhibitor Reduces Amyloid-ß Formation.

There is an urgent need for novel therapeutic approaches to treat Alzheimer's disease (AD) with the ability to both alleviate the clinical symptoms and halt the progression of the disease. AD is characterized by the accumulation of amyloid-ß (Aß) peptides which are generated through the sequential proteolytic cleavage of the amyloid precursor protein (APP). Previous studies reported that Mint2, a neuronal adaptor protein binding both APP and the γ-secretase complex, affects APP processing and formation of pathogenic Aß. However, there have been contradicting results concerning whether Mint2 has a facilitative or suppressive effect on Aß generation. Herein, we deciphered the APP-Mint2 protein-protein interaction (PPI) via extensive probing of both backbone H-bond and side-chain interactions. We also developed a proteolytically stable, high-affinity peptide targeting the APP-Mint2 interaction. We found that both an APP binding-deficient Mint2 variant and a cell-permeable PPI inhibitor significantly reduced Aß42 levels in a neuronal in vitro model of AD. Together, these findings demonstrate a facilitative role of Mint2 in Aß formation, and the combination of genetic and pharmacological approaches suggests that targeting Mint2 is a promising therapeutic strategy to reduce pathogenic Aß levels.

A High-Affinity Peptide Ligand Targeting Syntenin Inhibits Glioblastoma.

Despite the recent advances in cancer therapeutics, highly aggressive cancer forms, such as glioblastoma (GBM), still have very low survival rates. The intracellular scaffold protein syntenin, comprising two postsynaptic density protein-95/discs-large/zona occludens-1 (PDZ) domains, has emerged as a novel therapeutic target in highly malignant phenotypes including GBM. Here, we report the development of a novel, highly potent, and metabolically stable peptide inhibitor of syntenin, KSL-128114, which binds the PDZ1 domain of syntenin with nanomolar affinity. KSL-128114 is resistant toward degradation in human plasma and mouse hepatic microsomes and displays a global PDZ domain selectivity for syntenin. An X-ray crystal structure reveals that KSL-128114 interacts with syntenin PDZ1 in an extended noncanonical binding mode. Treatment with KSL-128114 shows an inhibitory effect on primary GBM cell viability and significantly extends survival time in a patient-derived xenograft mouse model. Thus, KSL-128114 is a novel promising candidate with therapeutic potential for highly aggressive tumors, such as GBM.

Unrecognised coeliac disease among men and women undergoing fertility treatment: A screening study.

BACKGROUND: Coeliac disease is an autoimmune disease triggered by dietary gluten and has been associated with several conditions influencing female and male reproduction. Due to unspecific symptoms, coeliac disease can be unrecognised for years. OBJECTIVE: To estimate the prevalence of unrecognised coeliac disease among couples referred to fertility treatment. METHODS: Cross-sectional screening for coeliac disease in men and women referred to fertility treatment using IgA tissue transglutaminase antibodies as a marker of coeliac disease and small-bowel biopsies to confirm the diagnosis. Participants answered a questionnaire on gluten intake, gastrointestinal symptoms and reproductive history. RESULTS: A total of 893 participants (51% women) were screened and eight were coeliac disease antibody positive. Small-bowel biopsies were obtained from seven antibody positive participants and unrecognised coeliac disease was confirmed in one woman and three men, corresponding to a prevalence of 0.45% (95% confidence interval 0.12-1.14). The total prevalence, combining already diagnosed and unrecognised CD cases, was 0.63% (95% confidence interval 0.29-1.12). CONCLUSION: The prevalence of unrecognised coeliac disease in a group of infertile patients was equivalent to that of the Danish general population and low compared with that observed in the majority of other screening studies of infertile patients. Surprisingly, it should be noted that more men than women had coeliac disease. This result does not support a need for routine screening among infertile patients.

Probing Backbone Hydrogen Bonds in Proteins by Amide-to-Ester Mutations.

All proteins contain characteristic backbones formed of consecutive amide bonds, which can engage in hydrogen bonds. However, the importance of these is not easily addressed by conventional technologies that only allow for side-chain substitutions. By contrast, technologies such as nonsense suppression mutagenesis and protein ligation allow for manipulation of the protein backbone. In particular, replacing the backbone amide groups with ester groups, that is, amide-to-ester mutations, is a powerful tool to examine backbone-mediated hydrogen bonds. In this minireview, we showcase examples of how amide-to-ester mutations can be used to uncover pivotal roles of backbone-mediated hydrogen bonds in protein recognition, folding, function, and structure.

Probing the Mint2 Protein-Protein Interaction Network Relevant to the Pathophysiology of Alzheimer's Disease.

The intracellular adaptor protein Mint2 binds amyloid precursor protein (APP) and presenilin-1, which are both central constituents of the amyloidogenic pathway associated with Alzheimer's disease (AD). Additional interaction partners have also been suggested for Mint2; several of them are also pertinent to AD pathogenesis. However, no comparative mapping of the Mint2 protein-protein interaction network is available. Here we provide a systematic characterization of seven interaction partners and address their specificities towards the different binding domains of Mint2, which reveal domain-specific and -nonspecific interaction partners. Moreover, we show that the last two C-terminal amino acids of Mint2 are both important for the intramolecular interaction with the PDZ1 domain and for the stability of Mint2.

Prevalence, incidence, and autoimmune comorbidities of celiac disease: a nation-wide, population-based study in Denmark from 1977 to 2016.

AIM: The aim of this study was to describe and identify potential trends with respect to prevalence, incidence, age, sex, and autoimmune comorbidity of celiac disease (CD). PATIENTS AND METHODS: A Danish nationwide cohort study of CD using data from The National Patient Register. Patients with a primary or secondary diagnosis code of CD during the period 1977 to 2016 were identified. Information on sex, date of birth, death, or immigration was obtained from the Danish Civil Registration System, and autoimmune comorbidities were identified in the Danish National Patient Register. The CD cohort was compared with the general Danish population using a control cohort and aggregated data obtained from Statistics Denmark. RESULTS: The CD cohort consisted of 11 802 (65% women) patients. The median age at diagnosis of CD varied between 30 years in 1980-1984 and 45 years in 1995-1999 and 27 years in 2015-2016. The prevalence of CD in 1986 and 2016 was 14 and 180 per 100 000 persons, respectively, with a female/male ratio changing from 1.3 to 2.0. Incidence rates (per 100 000 person-years) changed from 1.6 in 1980-1984 to 15.2 in 2015-2016, with the largest increase among females aged 0-9 years. In 2016, prevalence of autoimmune comorbidities was 16.4% among the CD patients compared with 5.3% in the general population. CONCLUSION: The prevalence of diagnosed CD has doubled every decade in Denmark from 1986 to 2016, and in the same period the female/male ratio has increased and the median age at diagnosis has decreased. The prevalence of autoimmune comorbidity in 2016 was three times higher among CD patients compared with the general Danish population.