Andrew Duong

Aerial development in Streptomyces coelicolor requires sortase activity.

Streptomyces coelicolor is a multicellular bacterium whose life cycle encompasses three differentiated states: vegetative hyphae, aerial hyphae and spores. Among the factors required for aerial development are the ‘chaplins’, a family of eight secreted proteins that coat the surface of aerial hyphae. Three chaplins (the ‘long’ chaplins, ChpA, B and C) possess an LAXTG‐containing C‐terminal sorting signal and are predicted sortase substrates. The five remaining ‘short’ chaplins are presumed to be associated with the cell surface through interactions with the long chaplins. We show here that two sortase enzymes, SrtE1 and SrtE2, cleave LAXTG‐containing peptides at two distinct positions in vitro, and are required for cell wall anchoring of ChpC in vivo. srtE1/E2 double mutants are delayed in aerial hyphae formation, do not sporulate and fail to display all short chaplins on their aerial surfaces. Surprisingly, these mutant characteristics were not shared by a long chaplin mutant, which exhibited only modest delays in aerial development, leading us to revise the current model of chaplin‐mediated aerial development. The sortase mutant phenotype, instead, appears to stem from an inability to transcribe aerial hyphae‐specific genes, whose products have diverse functions. This suggests that sortase activity triggers an important, and previously unknown, developmental checkpoint.

Crystal structure of the Streptomyces coelicolor sortase E1 transpeptidase provides insight into the binding mode of the novel class E sorting signal

Many species of Gram-positive bacteria use sortase transpeptidases to covalently affix proteins to their cell wall or to assemble pili. Sortase-displayed proteins perform critical and diverse functions for cell survival, including cell adhesion, nutrient acquisition, and morphological development, among others. Based on their amino acid sequences, there are at least six types of sortases (class A to F enzymes); however, class E enzymes have not been extensively studied. Class E sortases are used by soil and freshwater-dwelling Actinobacteria to display proteins that contain a non-canonical LAXTG sorting signal, which differs from 90% of known sorting signals by substitution of alanine for proline. Here we report the first crystal structure of a class E sortase, the 1.93 Å resolution structure of the SrtE1 enzyme from Streptomyces coelicolor. The active site is bound to a tripeptide, providing insight into the mechanism of substrate binding. SrtE1 possesses β3/β4 and β6/β7 active site loops that contact the LAXTG substrate and are structurally distinct from other classes. We propose that SrtE1 and other class E sortases employ a conserved tyrosine residue within their β3/β4 loop to recognize the amide nitrogen of alanine at position P3 of the sorting signal through a hydrogen bond, as seen here. Incapability of hydrogen-bonding with canonical proline-containing sorting signals likely contributes to class E substrate specificity. Furthermore, we demonstrate that surface anchoring of proteins involved in aerial hyphae formation requires an N-terminal segment in SrtE1 that is presumably positioned within the cytoplasm. Combined, our results reveal unique features within class E enzymes that enable them to recognize distinct sorting signals, and could facilitate the development of substrate-based inhibitors of this important enzyme family.

The h-Index of Editorial Board Members Correlates Positively With the Impact Factor of Sports Medicine Journals

Background: The h-index is a metric widely used to present both the productivity and impact of an author’s previous publications. Purpose: To evaluate and observe any correlations among the h-indices of 2015 editorial board members from 8 top sports medicine journals. Study Design: Systematic review. Methods: The sex, country of residence, degree, and faculty position of the editorial board members were identified using their respective scientific publication profiles. The h-index and other bibliometric indicators of these editorial board members were obtained using both the Web of Science (WoS) and Google Scholar (GS) databases. Nonparametric statistics were used to analyze differences in h-index values, and regression models were used to assess the ability of the editorial board member’s h-index to predict their journal’s impact factor (IF). Results: A total of 422 editorial board members were evaluated. The median h-index of all editors was 20 (interquartile range [IQR], 19) using GS and 15 (IQR, 15) using WoS. GS h-index values were 1.19 times higher than WoS, with significant correlation between these values (r 2 = 0.88, P = .0001). Editorial board members with a PhD had significantly higher h-indices than those without (GS, P = .0007; WoS, P = .0002), and full professors had higher h-indices than associate and assistant professors (GS, P = .0001; WoS, P = .0001). Overall, there were significant differences in the distribution of the GS (P < .0001) and WoS (P < .0001) h-indices of the editorial board members by 2014 IF of the journals. Both the GS h-index (β coefficient, 0.01228; 95% CI, 0.01035-0.01423; P < .0001) as well as the WoS h-index (β coefficient, 0.01507; 95% CI, 0.01265-0.01749; P < .0001) of editorial board members were significant predictors of the 2014 IF of their journal. Conclusion: The h-indices of editorial board members of top sports medicine journals are significant predictors of the IF of their respective journals.

Crystallization and preliminary X-ray diffraction analysis of motif N from Saccharomyces cerevisiae Dbf4.

The Cdc7-Dbf4 complex plays an instrumental role in the initiation of DNA replication and is a target of replication-checkpoint responses in Saccharomyces cerevisiae. Cdc7 is a conserved serine/threonine kinase whose activity depends on association with its regulatory subunit, Dbf4. A conserved sequence near the N-terminus of Dbf4 (motif N) is necessary for the interaction of Cdc7-Dbf4 with the checkpoint kinase Rad53. To understand the role of the Cdc7-Dbf4 complex in checkpoint responses, a fragment of Saccharomyces cerevisiae Dbf4 encompassing motif N was isolated, overproduced and crystallized. A complete native data set was collected at 100 K from crystals that diffracted X-rays to 2.75 A resolution and structure determination is currently under way.

Biomarkers in the serum, synovial fluid and articular cartilage show promising utility in patients with femoroacetabular impingement: a systematic review

Importance Biomarkers have promising potential to provide a cost-effective tool to identify patients with femoroacetabular impingement (FAI) who are most at risk and who may benefit most from early joint preservation surgery. Objective To assess the potential role of biomarkers in the diagnosis and prognosis of FAI. Evidence review Three databases (PubMed, Ovid (MEDLINE) and Embase) were searched on 20 August 2017 from database inception, and two reviewers independently and in duplicate screened the resulting literature. Methodological quality of all included papers was assessed using the Methodological Index for Non-Randomized Studies criteria. The results are presented in a narrative summary fashion using descriptive statistics including means, proportions and ranges. Findings Seven studies (one retrospective laboratory series and six controlled laboratory studies) were identified including a total of 227 patients. The mean age of the patients was 41.6 years (range: 13–80), with a mean follow-up period of 29.9 months (SD=3.2). Markers of articular cartilage breakdown, including cartilage oligomeric matrix protein (COMP) and fibronectin–aggrecan complex (FAC), were identified in high concentrations in the serum and synovial fluid of patients with FAI, respectively. Moreover, mRNA expression of catabolic cytokines in the articular cartilage of patients with FAI has been reported. Conclusions and relevance Although not yet used in clinical settings, several biomarkers of articular cartilage damage have been identified in the serum, synovial fluid and articular cartilage of patients with FAI. These findings provide promising insight into the potential role of biomarkers in guiding clinical practice and assisting with patient selection and preoperative counselling in patients with FAI and should be evaluated further. Level of evidence IV, systematic review of level III and IV studies.

Liquid Chromatography-Tandem Mass Spectrometry to Define Sortase Cleavage Products

Sortase enzymes have specific endopeptidase activity, cleaving within a defined pentapeptide sequence at the C-terminal end of their protein substrates. Here, we describe how monitoring sortase cleavage activity can be achieved using peptide substrates. Peptide cleavage can be readily analyzed by liquid chromatography/tandem mass spectrometry (LC/MS/MS), which allows for the precise definition of cleavage sites. This technique could be used to analyze the peptidase activity of any enzyme, and identify sites of cleavage within any peptide.

Arthroscopic-Assisted Latissimus Dorsi Tendon Transfer for Massive Rotator Cuff Tears: A Systematic Review:

Background: Arthroscopic-assisted latissimus dorsi tendon transfer (LDTT) has shown promising results with good outcomes in patients with massive rotator cuff tears (MRCTs), as reported by individual studies. However, to the best of the authors’ knowledge, no systematic review has been performed to assess the collective outcomes of these individual studies. Purpose/Hypothesis: The primary purpose of this study was to assess patient outcomes after arthroscopic-assisted LDTT for the management of MRCTs. The secondary objectives were to report on the management of MRCTs, including diagnostic investigations, surgical decision making, and arthroscopic techniques, as well as to evaluate the quality of evidence of the existing literature. It was hypothesized that nearly all patients were satisfied with arthroscopic-assisted LDTT and that they experienced improvements in pain symptoms, function, and strength after the procedure, with an overall complication rate of less than 10%. Study Design: Systematic review; Level of evidence, 4. Methods: The databases MEDLINE, Embase, and PubMed were searched from database inception (1946) until August 18, 2017, with titles, abstracts, and full-text articles screened independently by 2 reviewers. Inclusion criteria were English-language studies investigating arthroscopic-assisted LDTT for the management of MRCTs on patients of all ages. Conference papers, book chapters, review articles, and technical reports were excluded. The quality of the included studies was categorized by level of evidence and the Methodological Index for Non-Randomized Studies (MINORS) checklist. Results: In total, 8 studies (7 case series [median MINORS score, 7 of 16] and 1 prospective comparative study [median MINORS score, 14 of 24]) were identified; the studies included 258 patients (258 shoulders) with MRCTs treated with LDTT using arthroscopic-assisted techniques. The decision to pursue surgery was based on both clinical findings and investigations in 5 studies, investigations only in 2 studies, and clinical findings only in 1 study. Overall, 88% of patients were satisfied with the results of surgery and experienced significant improvement in their symptoms, including shoulder pain, strength, range of motion, and overall function, over a mean follow-up period of 34.3 months. Overall, there was a low rate of complications (7%) associated with the procedure. Conclusion: Arthroscopic-assisted LDTT for MRCTs provides patients with marked improvement in shoulder pain, strength, and function, and the procedure is associated with a low risk of complication. Further high-quality comparative studies are warranted to validate these findings in comparison with other operative techniques.

Primary Allograft ACL Reconstruction in Skeletally Immature Patients—A Systematic Review of Surgical Techniques, Outcomes, and Complications

The purpose of this systematic review is to ascertain the risk profile of allografts in primary anterior cruciate ligament reconstruction (ACLR) of skeletally immature patients. Three databases (PubMed, EMBASE, and MEDLINE) were searched for articles addressing primary ACLR in skeletally immature patients (i.e., open femoral and tibial physes). Inclusion criteria encompassed the use of allograft tissue with available postoperative outcomes data. The methodological index for non-randomized studies (MINORS) was used to assess all studies. Descriptive statistics such as means, 95% confidence intervals and standard deviations are presented where applicable. A total of 3,852 studies were screened, with 9 studies of a total of 406 skeletally immature patients (mean age 14.9 ± 1.2 years) satisfying inclusion criteria. The majority (98%) of included patients underwent complete transphyseal ACLR. Where specified, allograft options included Achilles tendon (AT) (66.5%), tibialis anterior tendon (7.6%), bone-patellar tendon (2.5%), and fascia lata (1.0%). The use of a bone block for the AT was reported in one patient (0.2%). Postoperatively, and where specified, patients achieved full range of motion (12.1%), had good Lysholm scores of 94 to 100 (8.1%), and a return to preinjury level athletic participation of 82.9% (8.4%). Complications (13.3%) included graft failures (7.9%), nonrevision reoperation (4.7%), and a combined leg length discrepancy and angular (valgus and extension) deformity (0.2%). There were no reported incidences of disease transmission. Although failure rates of primary allograft ACL reconstruction are acceptable compared with other studies of mainly autograft use in this young, high-risk population, there was a very low rate of clinically significant physeal damage. However, the relatively low quality of the included studies limits the ability to recommend routine use of allograft for ACLR in the skeletally immature patient. More robust studies with long-term follow-up data are necessary to better ascertain the influence of allograft choice on postoperative outcomes for these young patients. This is a Level IV study, systematic review of Levels III and IV studies.

What Is the State of the Evidence in Anterolateral Ligament Research

The anterolateral ligament (ALL) is a capsular structure of the knee that is the subject of increasing academic interest. This article reviewed recent ALL literature in terms of subject matter and quality. Although current literature focusing on the ALL is small and limited to level 4 and 5 evidence, it is rapidly expanding. Cadaveric studies describing ALL biomechanics are the most common study design, followed by radiographic studies. The methodologic quality of cadaveric studies focusing on the ALL is high. Clinically oriented research pertaining to the diagnosis, therapy, prevalence, or prognosis of injury to the ALL is presently lacking.

Safety and efficacy of arthroscopy in the setting of shoulder arthroplasty

Shoulder arthroplasty has become a reliable and reproducible method of treating a range of shoulder pathologies including fractures, osteoarthritis, and rotator cuff arthropathy. Although most patients experience favorable outcomes from shoulder arthroplasty, some patients suffer from persistent symptoms post-arthroplasty and it is these patients who present a unique diagnostic and therapeutic challenge. The role of arthroscopy in assessing and treating patients with symptomatic prosthetic joints elsewhere in the body has been established in recent literature. However, the range of pathology that can affect a prosthetic shoulder is distinct from the knee or the hip and requires careful and considered assessment if an accurate diagnosis is to be made. When used alongside other investigations in a comprehensive assessment protocol, arthroscopy can play an important role in the diagnosis and treatment of the problematic shoulder arthroplasty.