Partitioning the Apparent Temperature Sensitivity into Within- and Across-Taxa Responses: Revisiting the Difference between Autotrophic and Heterotrophic Protists.

AbstractConventional analyses suggest that the metabolism of heterotrophs is thermally more sensitive than that of autotrophs, implying that warming leads to pronounced trophodynamic imbalances. However, these analyses inappropriately combine within- and across-taxa trends. Our new analysis separates these, revealing that 92% of the difference in the apparent thermal sensitivity between autotrophic and heterotrophic protists does indeed arise from within-taxa responses. Fitness differences among taxa adapted to different temperature regimes only partially compensate for the positive biochemical relationship between temperature and growth rate within taxa, supporting the hotter-is-partially-better hypothesis. Our work highlights the importance of separating within- and across-taxa responses when comparing temperature sensitivities between groups, which is relevant to how trophic imbalances and carbon fluxes respond to warming.

"Surface Browsing" May Allow "Filter-Feeding" Protozoa to Exert Top-Down Control on Colony-Forming Toxic Cyanobacterial Blooms.

Blooms of the cyanobacterium Microcystis threaten aquatic ecosystems. Protozoa grazing can control unicellular Microcystis populations; however, Microcystis blooms are composed of multicellular colonies that are thought to prevent grazing. We show that this is not so: the model ciliate Paramecium has an impact on Microcystis populations through grazing, even when large colonies occur, and this leads to a corresponding decrease in toxic microcystins. Notably, as the number of large colonies increased, Paramecium exerted top-down control by altering its feeding behavior: once the colony size was >12-20 µm, Paramecium no longer acted as a "filter feeder"; instead, it became a "surface browser," grazing around and between larger colonies, removing individual Microcystis and small colonies. However, as the proportion of large colonies increased, exponentially reducing the surface area to volume ratio, the impact of Paramecium decreased exponentially. This study provides new insights into how protozoa may affect Microcystis populations through top-down control of blooms.

Ecology of planktonic ciliates in a changing world: Concepts, methods, and challenges.

Plankton ecologists ultimately focus on forecasting, both applied and environmental outcomes. We review how appreciating planktonic ciliates has become central to these predictions. We explore the 350-year-old canon on planktonic ciliates and examine its steady progression, which has been punctuated by conceptual insights and technological breakthroughs. By reflecting on this process, we offer suggestions as to where future leaps are needed, with an emphasis on predicting outcomes of global warming. We conclude that in terms of climate change research: (i) climatic hotspots (e.g. polar oceans) require attention; (ii) simply adding ciliate measurements to zooplankton/phytoplankton-based sampling programs is inappropriate; (iii) elucidating the rare biosphere's functional ecology requires culture-independent genetic methods; (iv) evaluating genetic adaptation (microevolution) and population composition shifts is required; (v) contrasting marine and freshwaters needs attention; (vi) mixotrophy needs attention; (vii) laboratory and field studies must couple automated measurements and molecular assessment of functional gene expression; (viii) ciliate trophic diversity requires appreciation; and (ix) marrying gene expression and function, coupled with climate change scenarios is needed. In short, continued academic efforts and financial support are essential to achieve the above; these will lead to understanding how ciliates will respond to climate change, providing tools for forecasting.

Detecting beta-amyloid glycation by intrinsic fluorescence - Understanding the link between diabetes and Alzheimer's disease.

We monitor early stages of beta-amyloid (Aß1-40) aggregation, one of the key processes leading to Alzheimer's disease (AD), in the presence of high glucose concentrations by measuring Aß1- 40 intrinsic fluorescence. The multiple peaks and their shifts observed in the time-resolved emission spectra (TRES) reveal the impact of glycation on Aß1- 40 oligomerisation. The results show that formation of the advanced glycation end products (AGEs) alters the aggregation pathway. These changes are highly relevant to our understanding of the pathophysiology of AD and the implication of AGE and diabetes in these pathways.

Lysyl oxidase-like 2 (LOXL2)-mediated cross-linking of tropoelastin.

Lysyl oxidases (LOXs) play a central role in extracellular matrix remodeling during development and tumor growth and fibrosis through cross-linking of collagens and elastin. We have limited knowledge of the structure and substrate specificity of these secreted enzymes. LOXs share a conserved C-terminal catalytic domain but differ in their N-terminal region, which is composed of 4 repeats of scavenger receptor cysteine-rich (SRCR) domains in LOX-like (LOXL) 2. We investigated by X-ray scattering and electron microscopy the low-resolution structure of the full-length enzyme and the structure of a shorter form lacking the catalytic domain. Our data demonstrate that LOXL2 has a rod-like structure with a stalk composed of the SRCR domains and the catalytic domain at its tip. We detected direct interaction between LOXL2 and tropoelastin (TE) and also LOXL2-mediated deamination of TE. Using proteomics, we identified several allysines together with cross-linked TE peptides. The elastin-like material generated was resistant to trypsin proteolysis and displayed mechanical properties similar to mature elastin. Finally, we detected the codistribution of LOXL2 and elastin in the vascular wall. Altogether, these data suggest that LOXL2 could participate in elastogenesis in vivo and could be used as a means of cross-linking TE in vitro for biomimetic and cell-compatible tissue engineering purposes.-Schmelzer, C. E. H., Heinz, A., Troilo, H., Lockhart-Cairns, M.-P., Jowitt, T. A., Marchand, M. F., Bidault, L., Bignon, M., Hedtke, T., Barret, A., McConnell, J. C., Sherratt, M. J., Germain, S., Hulmes, D. J. S., Baldock, C., Muller, L. Lysyl oxidase-like 2 (LOXL2)-mediated cross-linking of tropoelastin.

Minimally Invasive Repair of Ascending Aortic Pseudoaneurysms: An Alternative to Open Surgical Repair in High-Risk Patients.

Development of a pseudoaneurysm of the ascending aorta is an uncommon complication of aortic surgery. Several nonsurgical techniques are available for treatment of ascending aortic pseudoaneurysms (AAPs). This report outlines a single-center retrospective experience with 14 nonsurgical procedures for treatment of AAPs in 10 patients. Modified stent grafts, septal defect occlusion devices, coil embolics, and liquid embolics were deployed by transthoracic and endovascular approaches. Complete stasis of the AAP was achieved in 7 of 10 patients (70%). Mean postprocedural recoveries occurred within 3.5 days. Nonsurgical techniques for repair of AAPs offer a comparatively safe and effective alternative to open surgical repair.

Influence of local microenvironment on the double hydrogen transfer in porphycene.

We performed time-resolved transient absorption and fluorescence anisotropy measurements in order to study tautomerization of porphycene in rigid polymer matrices at cryogenic temperatures. Studies were carried out in poly(methyl methacrylate) (PMMA), poly(vinyl butyral) (PVB), and poly(vinyl alcohol) (PVA). The results prove that in all studied media hydrogen tunnelling plays a significant role in the double hydrogen transfer which becomes very sensitive to properties of the environment below approx. 150 K. We also demonstrate that there exist two populations of porphycene molecules in rigid media: "hydrogen-transferring" molecules, in which tautomerization occurs on time scales below 1 ns and "frozen" molecules in which double hydrogen transfer is too slow to be monitored with nanosecond techniques. The number of "frozen" molecules increases when the sample is cooled. We explain this effect by interactions of guest molecules with a rigid host matrix which disturbs symmetry of porphycene and hinders tunnelling. Temperature dependence of the number of hydrogen-transferring molecules suggests that the factor which restores the symmetry of the double-minimum potential well in porphycene are intermolecular vibrations localized in separated regions of the amorphous polymer.

[How Iexplore... The trauma-induced coagulopathy]. / Comment j'explore La coagulopathie induite du patient polytraumatisé.

The trauma-induced coagulopathy (TIC) is a frequent and serious pathology, whose clinical diagnosis remains arduous. It constitutes a real challenge in the management of these patients. In emergency situations, the management of TIC can lead the practitioner to administer blood products «blindly¼, ie without reliable monitoring in support. This exposes to the risk of using blood products by default or excess, at a time when stocks of blood banks are becoming more and more worrying, thus constituting a public health issue. In this article we propose the use of a viscoelastic technique by ROTEM® according to an algorithm to effectively guide the use of blood products.

La coagulopathie aiguë du traumatisé (CAT) est une pathologie fréquente, grave et dont le diagnostic clinique reste peu aisé. Elle constitue ainsi un véritable challenge dans la prise en charge des patients polytraumatisés. En situation d'urgence, la gestion de la CAT peut amener le praticien à administrer des produits sanguins «à l'aveugle¼, c'est-à-dire sans monitoring fiable à l'appui. Ceci expose à un risque d'usage de produits sanguins inadaptés, par défaut ou par excès, exposant ainsi le patient à un manque de correction ou aux effets secondaires liés à une administration inutile. Ceci est d'autant plus regrettable à une époque où les stocks des banques de sang deviennent de plus en plus préoccupants. La gestion adéquate de la CAT constitue ainsi un enjeu de santé publique. Dans cet article, nous proposons de décrire l'usage de la technique viscoélastique par thromboélastométrie (ROTEM®) afin de guider, plus efficacement, l'usage des produits sanguins.

False Exclusion: A Case to Embed Predator Performance in Classical Population Models.

We argue that predator-prey dynamics, a cornerstone of ecology, can be driven by insufficiently explored aspects of predator performance that are inherently prey dependent: that is, these have been falsely excluded. Classical (Lotka-Volterra-based) models tend to consider only prey-dependent ingestion rate. We highlight three other prey-dependent responses and provide empirically derived functions to describe them. These functions introduce neglected nonlinearities and threshold behaviors into dynamic models, leading to unexpected outcomes: specifically, as prey abundance increases predators (1) become less efficient at using prey; (2) initially allocate resources toward survival and then allocate resources toward reproduction; and (3) are less likely to die. Based on experiments using model zooplankton, we explore the consequences of including these functions in the classical structure and show that they alter qualitative and quantitative dynamics of an empirically informed generic predator-prey model. Through bifurcation analysis, our revised structure predicts (1) predator extinctions, where the classical structure allows persistence; (2) predator survival, where the classical structure drives predators toward extinction; and (3) greater stability through smaller amplitude of cycles, relative to the classical structure. Then, by exploring parameter space, we show how these responses alter predictions of predator-prey stability and competition between predators. In light of our results, we suggest that classical assumptions about predator responses to prey abundance should be reevaluated.

Atypical COL3A1 variants (glutamic acid to lysine) cause vascular Ehlers-Danlos syndrome with a consistent phenotype of tissue fragility and skin hyperextensibility.

PURPOSE: The Ehlers-Danlos syndromes (EDS) are a group of rare inherited connective tissue disorders. Vascular EDS (vEDS) is caused by pathogenic variants in COL3A1, most frequently glycine substitutions. We describe the phenotype of the largest series of vEDS patients with glutamic acid to lysine substitutions (Glu>Lys) in COL3A1, which were all previously considered to be variants of unknown significance. METHODS: Clinical and molecular data for seven families with three different Glu>Lys substitutions in COL3A1 were analyzed. RESULTS: These Glu>Lys variants were reclassified from variants of unknown significance to either pathogenic or likely pathogenic in accordance with American College of Medical Genetics and Genomics guidelines. All individuals with these atypical variants exhibited skin hyperextensibility as seen in individuals with classical EDS and classical-like EDS and evidence of tissue fragility as seen in individuals with vEDS. CONCLUSION: The clinical data demonstrate the overlap between the different EDS subtypes and underline the importance of next-generation sequencing gene panel analysis. The three different Glu>Lys variants point toward a new variant type in COL3A1 causative of vEDS, which has consistent clinical features. This is important knowledge for COL3A1 variant interpretation. Further follow-up data are required to establish the severity of tissue fragility complications compared with patients with other recognized molecular causes of vEDS.

Cu2+ Effects on Beta-Amyloid Oligomerisation Monitored by the Fluorescence of Intrinsic Tyrosine.

A non-invasive intrinsic fluorescence sensing of the early stages of Alzheimer's beta amyloid peptide aggregation in the presence of copper ions is reported. By using time-resolved fluorescence techniques the formation of beta amyloid-copper complexes and the accelerated peptide aggregation are demonstrated. The shifts in the emission spectral peaks indicate that the peptides exhibit different aggregation pathways than in the absence of copper.

Fibrillar Collagens.

Fibrillar collagens (types I, II, III, V, XI, XXIV and XXVII) constitute a sub-group within the collagen family (of which there are 28 types in humans) whose functions are to provide three-dimensional frameworks for tissues and organs. These networks confer mechanical strength as well as signalling and organizing functions through binding to cellular receptors and other components of the extracellular matrix (ECM). Here we describe the structure and assembly of fibrillar collagens, and their procollagen precursors, from the molecular to the tissue level. We show how the structure of the collagen triple-helix is influenced by the amino acid sequence, hydrogen bonding and post-translational modifications, such as prolyl 4-hydroxylation. The numerous steps in the biosynthesis of the fibrillar collagens are reviewed with particular attention to the role of prolyl 3-hydroxylation, collagen chaperones, trimerization of procollagen chains and proteolytic maturation. The multiple steps controlling fibril assembly are then discussed with a focus on the cellular control of this process in vivo. Our current understanding of the molecular packing in collagen fibrils, from different tissues, is then summarized on the basis of data from X-ray diffraction and electron microscopy. These results provide structural insights into how collagen fibrils interact with cell receptors, other fibrillar and non-fibrillar collagens and other ECM components, as well as enzymes involved in cross-linking and degradation.

Determination of the substrate repertoire of ADAMTS2, 3, and 14 significantly broadens their functions and identifies extracellular matrix organization and TGF-ß signaling as primary targets.

A disintegrin and metalloproteinase with thrombospondin type I motif (ADAMTS)2, 3, and 14 are collectively named procollagen N-proteinases (pNPs) because of their specific ability to cleave the aminopropeptide of fibrillar procollagens. Several reports also indicate that they could be involved in other biological processes, such as blood coagulation, development, and male fertility, but the potential substrates associated with these activities remain unknown. Using the recently described N-terminal amine isotopic labeling of substrate approach, we analyzed the secretomes of human fibroblasts and identified 8, 17, and 22 candidate substrates for ADAMTS2, 3, and 14, respectively. Among these newly identified substrates, many are components of the extracellular matrix and/or proteins related to cell signaling such as latent TGF-ß binding protein 1, TGF-ß RIII, and dickkopf-related protein 3. Candidate substrates for the 3 ADAMTS have been biochemically validated in different contexts, and the implication of ADAMTS2 in the control of TGF-ß activity has been further demonstrated in human fibroblasts. Finally, the cleavage site specificity was assessed showing a clear and unique preference for nonpolar or slightly hydrophobic amino acids. This work shows that the activities of the pNPs extend far beyond the classically reported processing of the aminopropeptide of fibrillar collagens and that they should now be considered as multilevel regulators of matrix deposition and remodeling.-Bekhouche, M., Leduc, C., Dupont, L., Janssen, L., Delolme, F., Vadon-Le Goff, S., Smargiasso, N., Baiwir, D., Mazzucchelli, G., Zanella-Cleon, I., Dubail, J., De Pauw, E., Nusgens, B., Hulmes, D. J. S., Moali, C., Colige, A. Determination of the substrate repertoire of ADAMTS2, 3, and 14 significantly broadens their functions and identifies extracellular matrix organization and TGF-ß signaling as primary targets.

Prehospital parameters can help to predict coagulopathy and massive transfusion in trauma patients.

BACKGROUND: This study aimed to evaluate the accuracy of prehospital parameters, including vital signs and resuscitation (fluids, vasopressor), to predict trauma-induced coagulopathy (TIC, fibrinogen <1·5 g/l or PTratio > 1·5 or platelet count <100 × 109 /l), and a massive transfusion (MT, ≥10 RBC units within the first 24 h). METHODS: From a trauma registry (2011-2015), in which patients are prospectively included, we retrospectively retrieved the heart rate (HR), systolic blood pressure (SBP), volume of prehospital fluids and administration of noradrenaline. We calculated the shock index (SI: HR/SBP), the MGAP prehospital triage score and the Injury Severity Score (ISS). We also identified patients who had positive criteria from the Resuscitation Outcome Consortium (ROC, SBP < 70 mmHg or SBP 70-90 and HR > 107 pulse/min). For these parameters, we drew a ROC curve and defined a cut-off value to predict TIC or MT. The strength of association between prehospital parameters and TIC as well as MT was assessed using logistic regression, and cut-off values were determined using ROC curves. RESULTS: Among the 485 patients included in the study, TIC was observed in 112 patients (23%) and MT in 22 patients (5%). For the prediction of TIC, ISS had good accuracy (AUC: 0·844, 95% confidence interval, CI: 0·799-0·879), as did the volume of fluids (>1000 ml) given during prehospital care (AUC: 0·801, 95% CI: 0·752-0·842). For the prediction of MT, ISS had excellent accuracy (AUC: 0·932, 95% CI: 0·866-0·966), whereas good accuracy was found for SI (> 0·9; AUC: 0·859, 95% CI: 0·705-0·936), vasopressor administration (AUC: 0·828, 95% CI: 0·736-0·890) and fluids (>1000 ml; AUC: 0·811, 95% CI: 0·737-0·867). Vasopressor administration, ISS and SI were independent predictors of TIC and MT, whereas fluid volume and ROC criteria were independent predictor of TIC but not MT. No independent relationship was found between MGAP and TIC or MT. CONCLUSIONS: Prehospital parameters including the SI and resuscitation may help to better identify the severity of bleeding in trauma patients and the need for blood product administration at admission.

Beyond the "Code": A Guide to the Description and Documentation of Biodiversity in Ciliated Protists (Alveolata, Ciliophora).

Recent advances in molecular technology have revolutionized research on all aspects of the biology of organisms, including ciliates, and created unprecedented opportunities for pursuing a more integrative approach to investigations of biodiversity. However, this goal is complicated by large gaps and inconsistencies that still exist in the foundation of basic information about biodiversity of ciliates. The present paper reviews issues relating to the taxonomy of ciliates and presents specific recommendations for best practice in the observation and documentation of their biodiversity. This effort stems from a workshop that explored ways to implement six Grand Challenges proposed by the International Research Coordination Network for Biodiversity of Ciliates (IRCN-BC). As part of its commitment to strengthening the knowledge base that supports research on biodiversity of ciliates, the IRCN-BC proposes to populate The Ciliate Guide, an online database, with biodiversity-related data and metadata to create a resource that will facilitate accurate taxonomic identifications and promote sharing of data.

Imaging Surveillance in Patients After a Benign Fine-Needle Aspiration Biopsy of the Thyroid: Associated Cost and Incidence of Subsequent Cancer.

OBJECTIVE: The objective of our study was to determine patterns and cost of imaging tumor surveillance in patients after a benign fine-needle aspiration (FNA) biopsy of the thyroid in a large teaching hospital as well as the rate of subsequent cancer detection. MATERIALS AND METHODS: This cohort study was approved by the appropriate institutional review board and complied with HIPAA. All patients who had a benign thyroid FNA biopsy between January 1, 1999, and December 31, 2003, were identified from an institutional pathology database. We gathered information from electronic medical records on imaging tumor surveillance and subsequent cancer detection. Cost was determined using the facility total relative value unit and the 2014 Hospital Outpatient Prospective Payment System conversion factor. RESULTS: Between January 1, 1999, and December 31, 2003, 1685 patients had a benign thyroid FNA biopsy, 800 (47.5%) of whom underwent follow-up imaging. These patients underwent 2223 thyroid ultrasound examinations, 606 ultrasound-guided thyroid FNA biopsies, 78 thyroid scintigraphy examinations, 168 neck CTs, and 53 neck MRIs at a cost of $529,874, $176,157, $39,622, $80,580, and $53,114, respectively, for a total cost of $879,347 or $1099 per patient. The mean length of follow-up was 7.3 years, during which time 19 (2.4%) patients were diagnosed with thyroid cancer at a cost of $46,281 per cancer. Seventeen (89.5%) were diagnosed with papillary carcinoma and two (10.5%) with Hurthle cell carcinoma. CONCLUSION: Over a 5-year period, about half of the patients who had a benign thyroid FNA biopsy underwent follow-up imaging at considerable cost with a small rate of subsequent malignancy.

Amyloid-binding compounds maintain protein homeostasis during ageing and extend lifespan.

Genetic studies indicate that protein homeostasis is a major contributor to metazoan longevity. Collapse of protein homeostasis results in protein misfolding cascades and the accumulation of insoluble protein fibrils and aggregates, such as amyloids. A group of small molecules, traditionally used in histopathology to stain amyloid in tissues, bind protein fibrils and slow aggregation in vitro and in cell culture. We proposed that treating animals with such compounds would promote protein homeostasis in vivo and increase longevity. Here we show that exposure of adult Caenorhabditis elegans to the amyloid-binding dye Thioflavin T (ThT) resulted in a profoundly extended lifespan and slowed ageing. ThT also suppressed pathological features of mutant metastable proteins and human ß-amyloid-associated toxicity. These beneficial effects of ThT depend on the protein homeostasis network regulator heat shock factor 1 (HSF-1), the stress resistance and longevity transcription factor SKN-1, molecular chaperones, autophagy and proteosomal functions. Our results demonstrate that pharmacological maintenance of the protein homeostatic network has a profound impact on ageing rates, prompting the development of novel therapeutic interventions against ageing and age-related diseases.

Did Gause Have a Yeast Infection?

We planned to develop predator-prey models using Paramecium and yeast, but they have not been empirically examined since work by Gause in the 1930s. Therefore, we evaluated if Paramecium aurelia ingests and grows on eight yeasts. Recognising that it ingested yeasts but could not grow, we assessed if it might grow on other yeasts, by empirically parameterising a predator-prey model that relies on ingestion, not growth. Simulations were compared to P. aurelia-yeast time-series data, from Gause. We hypothesised that if the model simulated predator-prey dynamics that mimicked the original data, then possibly P. aurelia could grow on yeast; simulations did not mimic the original data. Reviewing works by Gause exposed two issues: experiments were undoubtedly contaminated with bacteria, allowing growth on bacteria, not yeast; and the population cycle data cannot be considered a self-sustaining time series, as they were manipulated by adding yeast and ciliates. We conclude that past and future work should not rely on this system, for either empirical or theoretical evaluations. Finally, although we show that P. aurelia, P. caudatum, Euplotes patella, and Blepharisma sp. cannot grow on yeast, Tetrahymena pyriformis and Colpidium striatum can; these may provide models to explore predator-prey dynamics.

Proteolytic control of TGF-ß co-receptor activity by BMP-1/tolloid-like proteases revealed by quantitative iTRAQ proteomics.

The metalloproteinase BMP-1 (bone morphogenetic protein-1) plays a major role in the control of extracellular matrix (ECM) assembly and growth factor activation. Most of the growth factors activated by BMP-1 are members of the TGF-ß superfamily known to regulate multiple biological processes including embryonic development, wound healing, inflammation and tumor progression. In this study, we used an iTRAQ (isobaric tags for relative and absolute quantification)-based quantitative proteomic approach to reveal the release of proteolytic fragments from the cell surface or the ECM by BMP-1. Thirty-eight extracellular proteins were found in significantly higher or lower amounts in the conditioned medium of HT1080 cells overexpressing BMP-1 and thus, could be considered as candidate substrates. Strikingly, three of these new candidates (betaglycan, CD109 and neuropilin-1) were TGF-ß co-receptors, also acting as antagonists when released from the cell surface, and were chosen for further substrate validation. Betaglycan and CD109 proved to be directly cleaved by BMP-1 and the corresponding cleavage sites were extensively characterized using a new mass spectrometry approach. Furthermore, we could show that the ability of betaglycan and CD109 to interact with TGF-ß was altered after cleavage by BMP-1, leading to increased and prolonged SMAD2 phosphorylation in BMP-1-overexpressing cells. Betaglycan processing was also observed in primary corneal keratocytes, indicating a general and novel mechanism by which BMP-1 directly affects signaling by controlling TGF-ß co-receptor activity. The proteomic data have been submitted to ProteomeXchange with the identifier PXD000786 and doi: 10.6019/PXD000786 .

Procollagen C-proteinase enhancer grasps the stalk of the C-propeptide trimer to boost collagen precursor maturation.

Tight regulation of collagen fibril deposition in the extracellular matrix is essential for normal tissue homeostasis and repair, defects in which are associated with several degenerative or fibrotic disorders. A key regulatory step in collagen fibril assembly is the C-terminal proteolytic processing of soluble procollagen precursors. This step, carried out mainly by bone morphogenetic protein-1/tolloid-like proteinases, is itself subject to regulation by procollagen C-proteinase enhancer proteins (PCPEs) which can dramatically increase bone morphogenetic protein-1/tolloid-like proteinase activity, in a substrate-specific manner. Although it is known that this enhancing activity requires binding of PCPE to the procollagen C-propeptide trimer, identification of the precise binding site has so far remained elusive. Here, use of small-angle X-ray scattering provides structural data on this protein complex indicating that PCPE binds to the stalk region of the procollagen C-propeptide trimer, where the three polypeptide chains associate together, at the junction with the base region. This is supported by site-directed mutagenesis, which identifies two highly conserved, surface-exposed lysine residues in this region of the trimer that are essential for binding, thus revealing structural parallels with the interactions of Complement C1r/C1s, Uegf, BMP-1 (CUB) domain-containing proteins in diverse biological systems such as complement activation, receptor signaling, and transport. Together with detailed kinetics and interaction analysis, these results provide insights into the mechanism of action of PCPEs and suggest clear strategies for the development of novel antifibrotic therapies.