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Abstract: The structure of human coagulation factor XIII (FXIII), a heterotetrameric plasma protransglutaminase that covalently cross-links preformed fibrin polymers, remains elusive until today. The heterotetrameric complex is composed of 2 catalytic FXIII-A and 2 protective FXIII-B subunits. Structural etiology underlying FXIII deficiency has so far been derived from crystallographic structures, all of which are currently available for the FXIII-A2 homodimer only. Here, we present the cryogenic electron microscopy (cryo-EM) structure of a native, human plasma-derived FXIII-A2B2 complex at 2.4 Å resolution. The structure provides detailed information on FXIII subunit interacting interfaces as the 2 subunits interact strongly in plasma. The native FXIII-A2B2 complex reveals a pseudosymmetric heterotetramer of 2 FXIII-B monomers intercalating with a symmetric FXIII-A2 dimer forming a "crown"-like assembly. The symmetry axes of the A2 and B2 homodimers are twisted relative to each other such that Sushi domain 1 interacts with the catalytic core of the A subunit, and Sushi domain 2 with the symmetry related A' subunit, and vice versa. We also report 4 novel mutations in the F13A1 gene encoding the FXIII-A subunit from a cohort of patients with severe FXIII deficiency. Our structure reveals the etiological basis of homozygous and heterozygous pathogenic mutations and explains the conditional dominant negative effects of heterozygous mutations. This atomistic description of complex interfaces is consistent with previous biochemical data and shows a congruence between the structural biochemistry of the FXIII complex and the clinical features of FXIII deficiency., (© 2025 American Society of Hematology. Published by Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.)

The reaction center-light-harvesting complex 1 (RC-LH1) plays an essential role in the primary reactions of bacterial photosynthesis. Here, we present high-resolution structures of native monomeric and dimeric RC-LH1 supercomplexes from Rhodobacter ( Rba. ) blasticus using cryo-electron microscopy. The RC-LH1 monomer is composed of an RC encircled by an open LH1 ring comprising 15 αβ heterodimers and a PufX transmembrane polypeptide. In the RC-LH1 dimer, two crossing PufX polypeptides mediate dimerization. Unlike Rhodabacter sphaeroides counterpart, Rba. blasticus RC-LH1 dimer has a less bent conformation, lacks the PufY subunit near the LH1 opening, and includes two extra LH1 αβ subunits, forming a more enclosed S-shaped LH1 ring. Spectroscopic assays reveal that these unique structural features are accompanied by changes in the kinetics of quinone/quinol trafficking between RC-LH1 and cytochrome bc 1 . Our findings reveal the assembly principles and structural variability of photosynthetic RC-LH1 supercomplexes, highlighting diverse strategies used by phototrophic bacteria to optimize light-harvesting and electron transfer in competitive environments.

Introduction and Objectives: We aimed to assess the outcomes of patients with trigeminal neuralgia (TGN) who underwent Gamma Knife radiosurgery (GKRS)., Materials and Methods: Fifty-three patients with typical TGN underwent GKRS from May 2012 until December 2022. Among these patients, 45 patients who were follow-up for at least 12 months were included in the study. A mean dose of 87.5 Gy (range, 80-90) was administered to the trigeminal nerve. Postoperatively, outcome was considered excellent if the patient was pain- and medication-free., Results: The mean symtpom duration was 9.53 years, and the mean patient age was 59.8 years (range, 34-85). The mean follow-up period was 46.8 months (range, 12-127 months). 46.7% of patients had a history of previous surgical interventions. A single nerve division was affected in 14 patients (31.1%), and multiple divisions were affected in 31 patients (68.9%). The rate of initial pain relief was 80%. Hypoesthesia in the area of trigeminal nerve developed in 30 (66.7%). Twenty patients (44.4%) exhibited excellent results within 72.4 months. Recurrence occurred in 11 patients (24.4%) with 27.6 months., Conclusions: Our results suggest that GKRS is a safe and effective procedure. Thus, it is an attractive first- and second-line treatment choice for TGN., (Copyright © 2024 Sociedad Española de Neurocirugía. Published by Elsevier España, S.L.U. All rights reserved.)

Background and Aims: Blood disorders, such as sickle cell disease, and other clinical conditions are often accompanied by intravascular hemolytic events along with the development of severe coagulopathies. Hemolysis, in turn, leads to the accumulation of Fe(II/III)-protoporphyrin IX (heme) in the intravascular compartment, which can trigger a variety of proinflammatory and prothrombotic reactions. As such, heme binding to the blood coagulation proteins factor VIII (FVIII), fibrinogen, and activated protein C with functional consequences has been demonstrated earlier., Methods: We herein present an in-depth characterization of the FVIII-heme interaction at the molecular level and its (patho-)physiological relevance through the application of biochemical, biophysical, structural biology, bioinformatic, and diagnostic tools., Results: FVIII has a great heme-binding capacity with seven heme molecules associating with the protein. The respective binding sites were identified by investigating heme binding to FVIII-derived peptides in combination with molecular docking and dynamic simulation studies of the complex as well as cryo-electron microscopy, revealing three high-affinity and four moderate heme-binding motifs (HBMs). Furthermore, the relevance of the FVIII-heme complex formation was characterized in physiologically relevant assay systems, revealing a ~ 50 % inhibition of the FVIII cofactor activity even in the protein-rich environment of blood plasma., Conclusion: Our study provides not only novel molecular insights into the FVIII-heme interaction and its physiological relevance, but also strongly suggests the reduction of the intrinsic pathway and the accentuation of the final clotting step (by, for example, fibrinogen crosslinking) in hemolytic conditions as well as a future perspective in the context of FVIII substitution therapy of hemorrhagic events in hemophilia A patients., Competing Interests: Declaration of competing interest The authors declare no competing financial interests., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Complement is an important effector mechanism for antibody-mediated clearance of infections and tumor cells. Upon binding to target cells, the antibody's constant (Fc) domain recruits complement component C1 to initiate a proteolytic cascade that generates lytic pores and stimulates phagocytosis. The C1 complex (C1qr 2 s 2 ) consists of the large recognition protein C1q and a heterotetramer of proteases C1r and C1s (C1r 2 s 2 ). While interactions between C1 and IgG-Fc are believed to be mediated by the globular heads of C1q, we here find that C1r 2 s 2 proteases affect the capacity of C1q to form an avid complex with surface-bound IgG molecules (on various 2,4-dinitrophenol [DNP]-coated surfaces and pathogenic Staphylococcus aureus ). The extent to which C1r 2 s 2 contributes to C1q-IgG stability strongly differs between human IgG subclasses. Using antibody engineering of monoclonal IgG, we reveal that hexamer-enhancing mutations improve C1q-IgG stability, both in the absence and presence of C1r 2 s 2 In addition, hexamer-enhanced IgGs targeting S. aureus mediate improved complement-dependent phagocytosis by human neutrophils. Altogether, these molecular insights into complement binding to surface-bound IgGs could be important for optimal design of antibody therapies., Competing Interests: Competing interest statement: A.K., J.A.G.v.S., P.W.H.I.P., K.P.M.v.K., F.J.B., J. Schuurman, and S.H.M.R. are coinventors on a patent describing antibody therapies against S. aureus., (Copyright © 2021 the Author(s). Published by PNAS.)

The quaternary structure is an important feature regulating protein function. Native mass spectrometry contributes to untangling quaternary structures by preserving the integrity of protein complexes in the gas phase. Tandem mass spectrometry by collision-induced dissociation (CID) can then be used to release subunits from these intact complexes, thereby providing structural information on the stoichiometry and topology. Cumulatively, such studies have revealed the preferred release of peripheral subunits during CID. In contrast, here we describe and focus on dissociation pathways that release nonperipheral subunits from hetero-complexes in CID at high collision energies. We find that nonperipheral subunits are ejected with a high propensity, as a consequence of sequential dissociation events, upon initial removal of peripheral subunits. Alternatively, nonperipheral subunits can be released directly from a charge-reduced or an elongated intact complex. As demonstrated here for a range of protein assemblies, releasing nonperipheral subunits under controlled conditions may provide unique structural information on the stoichiometry and topology of protein complexes.

In striated muscles, molecular filaments are largely composed of long protein chains with extensive arrays of identically folded domains, referred to as "beads-on-a-string". It remains a largely unresolved question how these domains have developed a unique molecular profile such that each carries out a distinct function without false-positive readout. This study focuses on the M-band segment of the sarcomeric protein titin, which comprises ten identically folded immunoglobulin domains. Comparative analysis of high-resolution structures of six of these domains ‒ M1, M3, M4, M5, M7, and M10 ‒ reveals considerable structural diversity within three distinct loops and a non-conserved pattern of exposed cysteines. Our data allow to structurally interpreting distinct pathological readouts that result from titinopathy-associated variants. Our findings support general principles that could be used to identify individual structural/functional profiles of hundreds of identically folded protein domains within the sarcomere and other densely crowded cellular environments., Competing Interests: The authors have declared that no competing interests exist.

Introduction: Pediatric pituitary adenomas are rare lesions. Incidence is reported between 1 and 10% of all childhood brain tumors and between 3 and 6% of all surgically treated adenomas. Although pituitary adenomas present with symptoms of hormone hypersecretion or neurological disruptions secondary to mass effect, they are almost constantly benign. Characteristics of patients may vary in different studies according to age, gender, size of adenoma, hormonal activity, and recurrence rates., Methods: Data on consecutive pediatric patients who were operated for pituitary adenoma with endoscopic endonasal transsphenoidal surgery (EETS) and transsphenoidal microsurgery (TMS) in the Department of Neurosurgery, Istanbul University Cerrahpasa Medical Faculty, Istanbul, Turkey, in the Neurosurgical Unit of the San Matteo Hospital, Pavia, Italy, and in the Division of Neurological Surgery Department of Biotechnology and Life Sciences, University of Insubria-Varese, ASST Sette Laghi, Ospedale di Circolo e Fondazione Macchi, Varese, Italy, between July 1997 and May 2018, were analyzed. Twenty-seven patients (11 males and 16 females), who were 18 years old or younger at the time of surgery, were included in the study. Medical records, images, and operative notes of patients were retrospectively reviewed., Results: There were 16 females (59.3%) and 11 males (40.7%). Mean age was 15.3 ± 3.3 (4-18). Thirty-two surgical procedures were performed for 27 patients (6 children required second operation). Thirteen patients (48.14%) had Cushing's disease (CD), 5 patients (18.5%) had growth hormone (GH)-secreting adenoma, 5 patients (18.5%) had prolactinoma, and 4 patients (14.8%) had non-functional adenoma. Twenty-two patients (81.4%) met remission criteria, and 5 patients (18.5%) did not meet remission criteria. Four patients met remission criteria after the second operation., Conclusion: Transsphenoidal approach affords effective release of mass effect and not only restoration but also perpetuation of normal endocrine functions in the majority of pediatric pituitary adenoma patients. Satisfactory results are reported with both EETS and TMS in the literature. Despite the technical difficulties in pediatric age, transsphenoidal resection of adenoma is still the mainstay treatment that provides cure in pediatric patients.

Background: Osteopetrosis (OP) is a varied clinical condition caused by malfunction or insufficient development of osteoclasts, or both. Neurologic findings can occur because of osteopetrotic conditions restricting neural foramina through which the spinal cord, cranial nerves, or major vascular structures traverse the skull. Renal tubular acidosis (RTA) is a well-documented condition with OP. However, Chiari I malformation is rarely reported concomitantly with OP., Case Description: We present a patient with a known RTA who was admitted with a rapid progressive tetraparesis within 24 hours. Clinical and radiologic evaluation of the patient revealed OP with RTA together with Chiari I malformation and holocord hydromyelia. Management of the patient was started with correction of severe hypokalemia (K: 1.4 mEq/L), which resulted in dramatic improvement in tetraparesis. Two days later, a posterior fossa bone decompression with ventriculoperitoneal shunt placement during the same session led to prominent decrease in size of the ventricles and the hydromyelia on long-term follow-up., Conclusions: Patients with OP can exhibit many clinical conditions. However, our case involved an unusual and rapid progressive tetraparesis, which could confuse the management as necessitating an emergent posterior fossa decompression. Stabilizing the metabolic status of the patient facilitated elective surgery, which further improved patient's neurologic findings and diminished hydromyelia on long-term follow-up., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Objective: To review the results of sphenoid sinus lateral recess (SSLR) cerebrospinal fluid (CSF) leaks treated with the endoscopic endonasal minimal transpterygoid approach (EEMTPA) and to discuss the surgical technique and outcomes., Methods: We performed a retrospective analysis of 13 cases who underwent SSLR CSF leak repair through the EEMTPA in our clinic between September 2008 and December 2017. Demographic and etiological features with reconstruction and surgical outcomes were examined. Mean follow-up time was 6.1 years., Results: In regard to etiology, the SSLR CSF leaks included 9 patients with spontaneous, 2 patients with traumatic, and 2 with iatrogenic causes. CSF leak was at the left lateral recess in 8 cases and at right lateral recess in 5 cases. Nine patients had empty sella syndrome, and 11 patients had meningoencephaloceles in addition to SSLR CSF leaks. All patients underwent surgery through the EEMTPA, and a multilayer closure with tissue overlay grafts were used for reconstruction. A pedicled nasoseptal flap and/or pedicled middle turbinate flap were applied to the area of the leak in all cases. One patient had a persistent CSF leak and another had recurrence, both of which required revision surgery. Our overall success rate was 100%., Conclusions: EEMTPA is a safe and effective method that can be used to treat challenging pathologies at the SSLR, including CSF leaks accompanying meningoencephaloceles. Furthermore, the success rate of EEMTPA for SSLR CSF leaks can be increased by applying endoscopic skull base reconstruction techniques such as the pedicled nasoseptal flap and pedicled middle turbinate flap., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Object: To analyse the clinical, imaging and histopathological data of patients who were diagnosed to have Dysembrioplastic Neuroepithelial Tumour (DNET) and underwent surgery between 1995-2015., Materials and Methods: Age at seizure onset, age at surgery, gender, disease duration, seizure outcome of 44 patients were analysed together with Magnetic Resonance Imaging (MRI) of 21 patients. MRI types were classified as type 1 (cystic/polycystic-like, well-delineated, strongly hypointense T1), type 2 (nodularlike,heterogeneous), type 3 (dysplastic-like, iso/hyposignal T1, poor delineation, gray-white matter blurring)., Results: Histopathological classification revealed simple form in 19, complex in 14 and non-specific in 11 patients. Lobar distribution of the lesions was as follows: 21 Temporal (47.7%), 12 parietal (27.3%), 8 frontal (18.2%) and 3 occipital (6.8%). Type 1 MRI was observed in 10, type 2 was in 7, and type 3 in 4 patients on radiological evaluation. All cases with type 1 MRI corresponded to either simple or complex forms and all cases with type 3 MRI corresponded to nonspecific form. The histopathological distribution of cases with type 2 MRI was 4 as non-specific, 2 as simple, 1 as complex. There was no significant difference in the age of onset, age at operation and duration of epilepsy between the patients with different MRI subtypes. The majority of patients (N:36) had Engel I outcome (81,8%). In groups with Engel II and III outcome, duration of epilepsy was significantly higher (p:0,014) and simple form of DNET has significantly higher seizure freedom after surgery compared to complex and nonspecific forms of DNET (p:0,002)., Conclusion: Patients with DNET constitute a group with favorable outcomes after epilepsy surgery especially with early referral to surgery. Longer duration of epilepsy was associated with worse seizure outcome for DNET patients. There was significant correlation between radiological and histopathological types of DNET especially in type 1 and 3.

Danger patterns on microbes or damaged host cells bind and activate C1, inducing innate immune responses and clearance through the complement cascade. How these patterns trigger complement initiation remains elusive. Here, we present cryo-electron microscopy analyses of C1 bound to monoclonal antibodies in which we observed heterogeneous structures of single and clustered C1-immunoglobulin G1 (IgG1) hexamer complexes. Distinct C1q binding sites are observed on the two Fc-CH2 domains of each IgG molecule. These are consistent with known interactions and also reveal additional interactions, which are supported by functional IgG1-mutant analysis. Upon antibody binding, the C1q arms condense, inducing rearrangements of the C1r 2 s 2 proteases and tilting C1q's cone-shaped stalk. The data suggest that C1r may activate C1s within single, strained C1 complexes or between neighboring C1 complexes on surfaces., (Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

The classical complement pathway contributes to the natural immune defense against pathogens and tumors. IgG antibodies can assemble at the cell surface into hexamers via Fc:Fc interactions, which recruit complement component C1q and induce complement activation. Biophysical characterization of the C1:IgG complex has remained elusive primarily due to the low affinity of IgG-C1q binding. Using IgG variants that dynamically form hexamers efficient in C1q binding and complement activation, we could assess C1q binding in solution by native mass spectrometry and size-exclusion chromatography. Fc-domain deglycosylation, described to abrogate complement activation, affected IgG hexamerization and C1q binding. Strikingly, antigen binding by IgG hexamers or deletion of the Fab arms substantially potentiated complement initiation, suggesting that Fab-mediated effects impact downstream Fc-mediated events. Finally, we characterized a reconstituted 2,045.3 ± 0.4-kDa complex of intact C1 bound to antigen-saturated IgG hexamer by native mass spectrometry, providing a clear visualization of a complete complement initiation complex., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Complement activation by antibodies bound to pathogens, tumors, and self antigens is a critical feature of natural immune defense, a number of disease processes, and immunotherapies. How antibodies activate the complement cascade, however, is poorly understood. We found that specific noncovalent interactions between Fc segments of immunoglobulin G (IgG) antibodies resulted in the formation of ordered antibody hexamers after antigen binding on cells. These hexamers recruited and activated C1, the first component of complement, thereby triggering the complement cascade. The interactions between neighboring Fc segments could be manipulated to block, reconstitute, and enhance complement activation and killing of target cells, using all four human IgG subclasses. We offer a general model for understanding antibody-mediated complement activation and the design of antibody therapeutics with enhanced efficacy.