Ubiquiton-An inducible, linkage-specific polyubiquitylation tool

The posttranslational modifier ubiquitin regulates most cellular processes. Its ability to form polymeric chains of distinct linkages is key to its diverse functionality. Yet, we still lack the experimental tools to induce linkage-specific polyubiquitylation of a protein of interest in cells. Here, we introduce a set of engineered ubiquitin protein ligases and matching ubiquitin acceptor tags for the rapid, inducible linear (M1-), K48-, or K63-linked polyubiquitylation of proteins in yeast and mammalian cells. By applying the so-called "Ubiquiton" system to proteasomal targeting and the endocytic pathway, we validate this tool for soluble cytoplasmic and nuclear as well as chromatin-associated and integral membrane proteins and demonstrate how it can be used to control the localization and stability of its targets. We expect that the Ubiquiton system will serve as a versatile, broadly applicable research tool to explore the signaling functions of polyubiquitin chains in many biological contexts.

Fungal COP9 signalosome assembly requires connection of two trimeric intermediates for integration of intrinsic deneddylase

The conserved eight-subunit COP9 signalosome (CSN) is required for multicellular fungal development. The CSN deneddylase cooperates with the Cand1 exchange factor to control replacements of E3 ubiquitin cullin RING ligase receptors, providing specificity to eukaryotic protein degradation. Aspergillus nidulans CSN assembles through a heptameric pre-CSN, which is activated by integration of the catalytic CsnE deneddylase. Combined genetic and biochemical approaches provided the assembly choreography within a eukaryotic cell for native fungal CSN. Interactomes of functional GFP-Csn subunit fusions in pre-CSN deficient fungal strains were compared by affinity purifications and mass spectrometry. Two distinct heterotrimeric CSN subcomplexes were identified as pre-CSN assembly intermediates. CsnA-C-H and CsnD-F-G form independently of CsnB, which connects the heterotrimers to a heptamer and enables subsequent integration of CsnE to form the enzymatically active CSN complex. Surveillance mechanisms control accurate Csn subunit amounts and correct cellular localization for sequential assembly since deprivation of Csn subunits changes the abundance and location of remaining Csn subunits.

F-box receptor mediated control of substrate stability and subcellular location organizes cellular development of Aspergillus nidulans

Fungal growth and development are coordinated with specific secondary metabolism. This coordination requires 8 of 74 F-box proteins of the filamentous fungus Aspergillus nidulans. F-box proteins recognize primed substrates for ubiquitination by Skp1-Cul1-Fbx (SCF) E3 ubiquitin RING ligases and degradation by the 26S proteasome. 24 F-box proteins are found in the nuclear fraction as part of SCFs during vegetative growth. 43 F-box proteins interact with SCF proteins during growth, development or stress. 45 F-box proteins are associated with more than 700 proteins that have mainly regulatory roles. This corroborates that accurate surveillance of protein stability is prerequisite for organizing multicellular fungal development. Fbx23 combines subcellular location and protein stability control, illustrating the complexity of F-box mediated regulation during fungal development. Fbx23 interacts with epigenetic methyltransferase VipC which interacts with fungal NF-κB-like velvet domain regulator VeA that coordinates fungal development with secondary metabolism. Fbx23 prevents nuclear accumulation of methyltransferase VipC during early development. These results suggest that in addition to their role in protein degradation, F-box proteins also control subcellular accumulations of key regulatory proteins for fungal development.

Fast friends - Ubiquitin-like modifiers as engineered fusion partners

Ubiquitin and its relatives are major players in many biological pathways, and a variety of experimental tools based on biological chemistry or protein engineering is available for their manipulation. One popular approach is the use of linear fusions between the modifier and a protein of interest. Such artificial constructs can facilitate the understanding of the role of ubiquitin in biological processes and can be exploited to control protein stability, interactions and degradation. Here we summarize the basic design considerations and discuss the advantages as well as limitations associated with their use. Finally, we will refer to several published case studies highlighting the principles of how they provide insight into pathways ranging from membrane protein trafficking to the control of epigenetic modifications.

Linkage reprogramming by tailor-made E3s reveals polyubiquitin chain requirements in DNA-damage bypass

A polyubiquitin chain can adopt a variety of shapes, depending on how the ubiquitin monomers are joined. However, the relevance of linkage for the signaling functions of polyubiquitin chains is often poorly understood because of our inability to control or manipulate this parameter in vivo. Here, we present a strategy for reprogramming polyubiquitin chain linkage by means of tailor-made, linkage- and substrate-selective ubiquitin ligases. Using the polyubiquitylation of the budding yeast replication factor PCNA in response to DNA damage as a model case, we show that altering the features of a polyubiquitin chain in vivo can change the fate of the modified substrate. We also provide evidence for redundancy between distinct but structurally similar linkages, and we demonstrate by proof-of-principle experiments that the method can be generalized to targets beyond PCNA. Our study illustrates a promising approach toward the in vivo analysis of polyubiquitin signaling.

The coronal hypomochlion: a tipping point of clinical relevance when planning valgus producing high tibial osteotomies

AIMS

In patients undergoing medial opening wedge high tibial osteotomy (MOWHTO), soft tissue opening on the medial side of the knee is difficult to predict. When the load bearing axis is corrected beyond a certain point, the knee joint tilts open on the medial side. We therefore hypothesised that there is a tipping point and defined this as the coronal hypomochlion.

PATIENTS AND METHODS

In this prospective study of 150 navigated MOWHTOs (144 consecutive patients), data were collected before surgery and at three months post-operatively. In order to calculate the hypomochlion, we compared the respective changes to the joint line convergence angle (JLCA) with the post-operative axis of the leg. The change to the medial proximal tibial angle accounts for only about 80% of the change to the femorotibial angle; 20% of the correction can therefore be attributed to non-osseous, soft-tissue changes.

RESULTS

We were able to demonstrate a linear change of JLCA in a range of 0° to 5° of valgus which started when the post-operative long-leg axis was corrected beyond 2° of valgus.

CONCLUSION

We found that the coronal hypomochlion occurs at 2° of valgus.

TAKE HOME MESSAGE

It is recommended to plan realignment for medial open wedge high tibial osteotomy at a maximum of 2° valgus. Cite this article: Bone Joint J 2016;98-B:628-33.

The devil is in the details: comparison between COP9 signalosome (CSN) and the LID of the 26S proteasome

The COP9 signalosome (CSN) and the proteasomal LID are conserved macromolecular complexes composed of at least eight subunits with molecular weights of approximately 350 kDa. CSN and LID are part of the ubiquitin–proteasome pathway and cleave isopeptide linkages of lysine side chains on target proteins. CSN cleaves the isopeptide bond of ubiquitin-like protein Nedd8 from cullins, whereas the LID cleaves ubiquitin from target proteins sentenced for degradation. CSN and LID are structurally and functionally similar but the order of the assembly pathway seems to be different. The assembly differs in at least the last subunit joining the pre-assembled subcomplex. This review addresses the similarities and differences in structure, function and assembly of CSN and LID.

Integration of the catalytic subunit activates deneddylase activity in vivo as final step in fungal COP9 signalosome assembly

The eight-subunit COP9 signalosome (CSN) is conserved from filamentous fungi to humans and functions at the interface between cellular signalling and protein half-life control. CSN consists of six PCI and two MPN domain proteins and forms a scaffold for additional interacting proteins. CSN controls protein stability in the ubiquitin-proteasome system where the MPN domain CSN5/CsnE subunit inactivates cullin-RING ligases. The CSN5/CsnE isopeptidase functions as deneddylase and removes the ubiquitin-like protein Nedd8. The six PCI domain proteins of human CSN form a horseshoe-like ring and all eight subunits are connected by a bundle of C-terminal α-helices. We show that single deletions of any csn subunit of Aspergillus nidulans resulted in the lack of deneddylase activity and identical defects in the coordination of development and secondary metabolism. The CSN1/CsnA N-terminus is dispensable for deneddylase activity but required for asexual spore formation. Complex analyses in mutant strains revealed the presence of a seven-subunit pre-CSN without catalytic activity. Reconstitution experiments with crude extracts of deletion strains and recombinant proteins allowed the integration of CSN5/CsnE into pre-CSN resulting in an active deneddylase. This supports a stable seven subunit pre-CSN intermediate where deneddylase activation in vivo can be controlled by CSN5/CsnE integration as final assembly step.

[Secondary deformities after section of primary bone tumors of the spine in children and adolescents]

Primary bone tumors and tumor-like lesions of the vertebral column are rare in children. After operative tumor resection, 25 children under the age of 17 could be reviewed in a retrospective analysis. Malignant bone tumors occurred only twice in the region of the vertebral body. No deformity was registered in 9 of 16 cases after local tumor resection with and without laminectomy on one level. In contrast, after resection of one or both facets in combination with laminectomy cranial to L4 or thoracal, progressive kyphosis was found within 6-22 months postoperatively in four cases. This required a secondary fusion. After primary fusion and instrumentation, no deformity was registered. In nine cases with a location of the tumor in the vertebral body, only two patients developed a secondary instability of the spine. Both cases had no primary fusion. The other seven patients with initial fusion and instrumentation showed no deformity within 24 up to 127 months postoperatively. These results are compared with data from the current literature.

[Functional capacity after peripheral nerve lesion: significance of pain syndromes]

INTRODUCTION

The loss of functional capacity by peripheral nerve lesion is easy to be estimated: A certain neurologic dysfunction results in a characteristic reduction of the former individual capacity. In contrast, the effect of accompanying pain to every-day life and working ability is not known exactly. In this study, we compared the results of judgement in nerve lesions under the circumstances of additional pain syndromes.

METHODS

From January 1994 until December 1998 we saw 57 patients with peripheral nerve lesions, part of them with an additional pain syndrome. Beside conventional neurological examination a detailed pain analysis has been done.

RESULTS

Lesions of the median or ulnar nerves showed regularly disturbances in neurological functions (10/14 for the median nerve, 13/16 for the ulnar nerve). Astonishing is the fact, that serious pain after nerve lesion only occurs in cases of partial nerve lesion. We saw neuralgias in 6 patients with ulnar neuropathy, in three cases of median nerve lesions we could see severe neuralgia (causalgia we found in 3 cases of ulnar neuropathy, in 6 cases after Median Nerve lesion). Patients with a lesion of the central plexus brachialis showed in 10 of 11 cases an additional pain syndrome. Other nerves have been affected more rarely. For the judgement of the loss of earning capacity we saw an additional pain related diminuition of at least 10% compared to those patients without pain problems.

CONCLUSIONS

The common grading scales for peripheral nerve lesions are not suitable in cases accompanied by an additional pain syndrome. Beside a functional deficit the effect of severe pain in these patients has to be estimated. On an average, patients with additional pain-problems get a 10% extended loss of earning capacity, even more in particular cases.

Perceptions of quality in long-term care: a satisfaction survey

At a 387-bed geriatric hospital in Montreal, Canada, a cross-sectional satisfaction survey was conducted on random samples of patients, families, families of deceased patients, and nursing staff. Using the same pretested structured questionnaire, the subjects were asked to rank (assign importance to) and rate (assign a rate of success to) 15 indicators of quality care. Significant differences both between and within the four groups were found on the perceived importance and rate of success of many of the indicators, supporting the primary hypotheses. Ethnicity and several sociodemographic covariates influenced the importance and rate of success assigned to the key indicators. The article discusses survey methodology issues as well as the integration of a satisfaction survey into an overall quality improvement program.

[Measuring vibration sense in childhood. Normal values and initial experiences in polyneuropathies]

BACKGROUND

We have attempted to obtain normal values for vibration thresholds in children and to evaluate their application in polyneuropathies.

METHODS

Vibration thresholds determinations were made by means of a handheld vibrameter (Fa Somedic AB Sweden): Within a constant frequency (100 Hz) and a calibrated pressure (450 g) the amplitude ranged variably from 0.01 to 399 microns. Measurements were made at three sites (carpal, tibial and tarsal). Vibration threshold (VT) was determined by the average of Vibration Perception Threshold (VPT) and Vibration Disappearance Threshold (VDT).

RESULTS

Reference values obtained from 106 children and adolescents (control group), 5.5 to 19 years of age, correlated with age but not with sex. The amplitude of VT-values ranged from 0.4 microns (carpal at 6 years), to 1.10 microns (tarsal at 18 years). Patients with Friedreich's ataxia (n = 7) or hereditary motosensory neuropathy (n = 11) showed strongly increased thresholds at all sites up to a factor of 100.

CONCLUSIONS

The examination by means of a vibrameter took at least 10 min, the shorter examination by tuning fork however showed to be less sensitive and rather inexact. An examination with a vibrameter is, as rule, reliably possible in children older than 5 years.