Cryo-EM structure of the E. coli translating ribosome in complex with SRP and its receptor

We report the 'early' conformation of the Escherichia coli signal recognition particle (SRP) and its receptor FtsY bound to the translating ribosome, as determined by cryo-EM. FtsY binds to the tetraloop of the SRP RNA, whereas the NG domains of the SRP protein and FtsY interact weakly in this conformation. Our results suggest that optimal positioning of the SRP RNA tetraloop and the Ffh NG domain leads to FtsY recruitment

Neuroendocrine tumors involving the gastroenteropancreatic tract: a clinicopathological evaluation of 773 cases

OBJECTIVE: Description of some of the clinical pathological characteristics of neuroendocrine tumors of the gastroenteropancreatic tract in Brazilian patients. INTRODUCTION: Neuroendocrine tumors arise in many organs and share common pathological features. In 2010, the World Health Organization published a new classification for neuroendocrine tumors using a three-tiered system that applies the terms neuroendocrine tumor Grade 1, neuroendocrine tumor Grade 2, and neuroendocrine carcinoma. The tumor grades are based on their mitotic rate and the Ki-67 index. In Brazil, information on neuroendocrine tumors of gastroenteropancreatic tract is scarce. METHODS: This study investigated clinicopathological features of 773 Brazilian gastroenteropancreatic neuroendocrine tumor cases from all the geographic regions of Brazil. All of the cases emerged from the files of a single institution (a large pathology reference laboratory) between 1997 and 2009. In addition, the gastroenteropancreatic neuroendocrine tumors were graded according to the new 2010 World Health Organization classification. RESULTS: Overall there were a higher number of neuroendocrine tumors in female over male. The lower ages were seen in patients with appendiceal tumors. The most common anatomic location involved was stomach followed by small and large intestines. All cases involving the appendix were of grade 1 and 92.1% of the neuroendocrine tumors of the esophagus were neuroendocrine carcinomas (grade 3). CONCLUSIONS: In this series, the proportion of NET cases in the total number of surgical pathology cases at our institution over the past 12 years is increasing

Granuloma facial: uma doença rara sob uma perspectiva dermatoscópica

The granuloma faciale is a rare and benign skin disease of unknown etiology, characterized by chronic leukocitoclastic vasculitis. It is characterized by skin lesions predominantly facial whose course is chronic and slowly progressive. The diagnosis is based on clinical features, histopathology and, more recently, in dermoscopy. We describe the case of a male patient, 40 years old, with a sarcoid lesion on the malar site, whose histopathological examination revealed a mixed inflammatory infiltrate with presence of Grenz zone. Dermoscopy revealed a pink background with white striations. The definitive diagnosis is made by histopathologic evaluation, and dermatoscopy can be helpful. It is known to be resistant to therapy, oral medications, intralesional and surgical procedures are options.O granuloma facial é doença cutânea rara e benigna, de etiologia desconhecida, caracterizado por vasculite leucocitoclástica crônica. Caracteriza-se por lesões cutâneas predominantemente faciais, tem curso crônico e lentamente progressivo. O diagnóstico é baseado na clínica, histopatologia e, mais recentemente, na dermatoscopia. Relatamos o quadro de um paciente masculino, 40 anos de idade, com lesão sarcoídea na face malar, cujo exame histopatológico revelou infiltrado inflamatório misto com presença de zona de Grenz. A dermatoscopia revelou um fundo rosado com estrias brancas. O diagnóstico definitivo é feito pela avaliação histopatológica, sendo que a dermatoscopia pode ser útil. É conhecida por ser resistente à terapêutica, sendo propostas medicações orais, intralesionais e procedimentos cirúrgicos.Federal University of Goiás Department of DermatologyPathologist at the Pathology Consulting Service - Botucatu (SP)Federal University of São PauloFederal University of GoiásUNIFESPSciEL

Conformational States of a Bacterial α2-Macroglobulin Resemble Those of Human Complement C3

α2 macroglobulins (α2Ms) are broad-spectrum protease inhibitors that play essential roles in the innate immune system of eukaryotic species. These large, multi-domain proteins are characterized by a broad-spectrum bait region and an internal thioester, which, upon cleavage, becomes covalently associated to the target protease, allowing its entrapment by a large conformational modification. Notably, α2Ms are part of a larger protein superfamily that includes proteins of the complement system, such as C3, a multi-domain macromolecule which is also characterized by an internal thioester-carrying domain and whose activation represents the pivotal step in the complement cascade. Recently, α2M/C3-like genes were identified in a large number of bacterial genomes, and the Escherichia coli α2M homolog (ECAM) was shown to be activated by proteases. In this work, we have structurally characterized ECAM by electron microscopy and small angle scattering (SAXS) techniques. ECAM is an elongated, flexible molecule with overall similarities to C3 in its inactive form; activation by methylamine, chymotrypsin, or elastase induces a conformational modification reminiscent of the one undergone by the transformation of C3 into its active form, C3b. In addition, the proposed C-terminus of ECAM displays high flexibility and different conformations, and could be the recognition site for partner macromolecules. This work sheds light on a potential bacterial defense mechanism that mimics structural rearrangements essential for activation of the complement cascade in eukaryotes, and represents a possible novel target for the development of antibacterials

Direct visualization reveals dynamics of a transient intermediate during protein assembly

Interactions between proteins underlie numerous biological functions. Theoretical work suggests that protein interactions initiate with formation of transient intermediates that subsequently relax to specific, stable complexes. However, the nature and roles of these transient intermediates have remained elusive. Here, we characterized the global structure, dynamics, and stability of a transient, on-pathway intermediate during complex assembly between the Signal Recognition Particle (SRP) and its receptor. We show that this intermediate has overlapping but distinct interaction interfaces from that of the final complex, and it is stabilized by long-range electrostatic interactions. A wide distribution of conformations is explored by the intermediate; this distribution becomes more restricted in the final complex and is further regulated by the cargo of SRP. These results suggest a funnel-shaped energy landscape for protein interactions, and they provide a framework for understanding the role of transient intermediates in protein assembly and biological regulation

Plastid thylakoid architecture optimizes photosynthesis in diatoms

Photosynthesis is a unique process that allows independent colonization of the land by plants and of the oceans by phytoplankton. Although the photosynthesis process is well understood in plants, we are still unlocking the mechanisms evolved by phytoplankton to achieve extremely efficient photosynthesis. Here, we combine biochemical, structural and in vivo physiological studies to unravel the structure of the plastid in diatoms, prominent marine eukaryotes. Biochemical and immunolocalization analyses reveal segregation of photosynthetic complexes in the loosely stacked thylakoid membranes typical of diatoms. Separation of photosystems within subdomains minimizes their physical contacts, as required for improved light utilization. Chloroplast 3D reconstruction and in vivo spectroscopy show that these subdomains are interconnected, ensuring fast equilibration of electron carriers for efficient optimum photosynthesis. Thus, diatoms and plants have converged towards a similar functional distribution of the photosystems although via different thylakoid architectures, which likely evolved independently in the land and the ocean.ISSN:2041-172

Solitary Primary Gastric Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is a relatively rare subgroup of non-Hodgkin's lymphoma that is characterized by an aggressive and severe disease course with frequent involvement of regional lymph nodes and/or early metastasis. Because most cases of MCL are diagnosed in the advanced stages, clinical data on extranodal or early stage MCL is lacking, and MCL that is both extranodal and diagnosed during the early stages is even more rare. There have been several case reports on primary gastric MCL, which comprise a type of extranodal MCLs. However, to our knowledge, there have been no reports on solitary primary gastric MCL without regional lymph node involvement or distant metastasis. Recently, the authors experienced an uncommon case of MCL with the aforementioned characteristics that was managed with chemotherapy followed by allogenic stem cell transplantation

Structural basis of signal sequence surveillance and selection by the SRP–FtsY complex

Signal-recognition particle (SRP)-dependent targeting of translating ribosomes to membranes is a multistep quality-control process. Ribosomes that are translating weakly hydrophobic signal sequences can be rejected from the targeting reaction even after they are bound to the SRP. Here we show that the early complex, formed by Escherichia coli SRP and its receptor FtsY with ribosomes translating the incorrect cargo EspP, is unstable and rearranges inefficiently into subsequent conformational states, such that FtsY dissociation is favored over successful targeting. The N-terminal extension of EspP is responsible for these defects in the early targeting complex. The cryo-electron microscopy structure of this 'false' early complex with EspP revealed an ordered M domain of SRP protein Ffh making two ribosomal contacts, and the NG domains of Ffh and FtsY forming a distorted, flexible heterodimer. Our results provide a structural basis for SRP-mediated signal-sequence selection during recruitment of the SRP receptor