Biochemical characterization of the SgcA1 alpha-D-glucopyranosyl-1-phosphate thymidylyltransferase from the enediyne antitumor antibiotic C-1027 biosynthetic pathway and overexpression of sgcA1 in Streptomyces globisporus to improve C-1027 production

Sequence analysis of the biosynthetic gene cluster for the enediyne antitumor antibiotic C-1027 from Streptomyces globisporus has previously suggested that the sgcA1 gene encodes a alpha-d-glucopyranosyl-1-phosphate thymidylyltransferase (Glc-1-P-TT) catalyzing the first step in the biosynthesis of the 4-deoxy-4-(dimethylamino)-5,5-dimethyl-d-ribopyranose moiety by activating alpha-d-glucopyranosyl-1-phosphate (Glc-1-P) into deoxythymidine diphosphate-alpha-d-glucose (dTDP-Glc). Here we report the overexpression of sgcA1 in E. coli, purification of the overproduced SgcA1 to homogenetity, biochemical and kinetic characterization of the purified SgcA1 as a Glc-1-P-TT, and yield improvement for C-1027 production by overexpression of sgcA1 and its flanking gene in S. globisporus. These findings provide biochemical evidence supporting the genetics-based hypothesis for C-1027 biosynthesis, set the stage for further investigation of the deoxysugar biosynthetic pathway, and demonstrate the utility of sugar biosynthesis genes in natural product yield improvement via combinatorial biosynthesis methods. In contrast to the homotetrameric quaternary structure known for Glc-1-P-TT enzymes from primary metabolic pathways, Glc-1-P-TT enzymes such as SgcA1 from secondary metabolic pathways are monomeric in solution. Sequence differences between the two subclasses of Glc-1-P-TT enzymes were noted. The monomeric structural feature of the latter enzymes could be exploited in engineering Glc-1-P-TT enzymes with broad substrate specificity for structural diversity via the glycorandomization strategy.     

Educational attainment, positive psychological mediators, and resources for health and vitality in older adults

Objectives: To further explain the relationship of education to health by a prospective examination of positive psychological states as mediators. Furthermore, to examine the resources of desirable events, self-esteem, and social support as possible mediators between positive psychological states and subsequent health and vitality. Methods: Four in-home interviews were conducted at 6-month intervals with a probability sample of 1,277 older adults (aged 55 and older); multiple regression was used to estimate mediating effects. Results: Positive states mediated the education relationship to both symptoms and vitality, independent of negative states; the resource measures did not mediate the positive state-health relationship. Discussion: Higher education level appears to increase the likelihood of being serene and happy, and healthy and vital, in later years; positive psychological states appeared to have both a promotion function (for vitality) and protective function (against health symptoms); self-esteem showed promise as a possible mediator of the effects of psychological states on health.     

Meniscal and chondral loss in the anterior cruciate ligament injured knee

Rupture of the anterior cruciate ligament (ACL) of the knee is a commonly occurring injury in the athletic population. Associated meniscal and chondral injury is well recognised. This occurs both at the time of index injury and also secondarily over time in the ACL-deficient knee as a result of several related pathways culminating in osteoarthritis. ACL reconstruction is a well established surgical technique for treatment of symptomatic instability in ACL-deficient knees but the role of ACL reconstruction in the prevention of osteoarthritis remains unclear. This article reviews the contemporary literature on the pathophysiology of chondral and meniscal loss in ACL-injured knees and the role of current treatment techniques, including surgical reconstruction of ligamentous, meniscal and chondral pathology, in altering the natural history of the ACL-deficient knee.     

Topographical analysis of the structural,biochemical and dynamic biomechanical properties of cartilage in an ovine model of osteoarthritis

OBJECTIVE: The relationship between the topographical variations in the structural, biochemical and dynamic biomechanical properties of articular cartilage (AC) before and 6 months after meniscectomy has not been previously reported but is clearly relevant to our understanding of the role of mechanical factors on the pathogenesis of osteoarthritis (OA). The objective of this study was to address this deficiency using an ovine model of OA induced by bilateral lateral meniscectomy. DESIGN: The dynamic effective shear modulus (G*) and phase lag were determined ex vivo at 26 individual locations over the medial and lateral tibial plateaux of non-operated and meniscectomized ovine joints 6 months after surgery using a novel hand-held dynamic indentation probe. AC thickness was measured with a needle penetration probe. The AC from the same topographical locations as indented was then analysed for sulfated glycosaminoglycans (S-GAG) as a measure of proteoglycan (PG) levels, collagen and water content. Histological evaluation of the collagen organization using quantitative analysis of birefringence intensity was performed on stained tissue sections from the same topographical locations of each animal. RESULTS: It was demonstrated that the AC of the entire lateral tibial compartment of the meniscectomized joints underwent significant local degenerative and compensatory changes as indicated by a decreased G* and an increase in phase lag and water content. This was accompanied by a decrease in PG content of the AC of the middle and inner regions. While the AC of the outer region of the lateral meniscectomized compartment showed a marked increase in PG content and a more than two-fold increase in thickness, these tissues were also found to be structurally inferior, as indicated by a decreased G* and abnormal collagen birefringence intensity. The AC thickness was elevated at all locations of the lateral and medial tibial plateau of the meniscectomized joints. Strong and significant correlations between the biomechanical and biochemical data were established for a number of the parameters examined, especially between collagen content and G*, collagen content and AC thickness, and G* and AC thickness. An inverse correlation between S-GAG content and G* was only apparent in non-operated control tissues, whereas correlations between collagen and water content, water content and G*, and water content and thickness were evident for AC of the meniscectomized tibial plateaux. Less striking changes were noted in the medial compartment where the intact meniscus remained in place. However, elevated PG content, thicker AC together with slight changes in G* suggested an early hypertrophic response in these tissues. CONCLUSION: This study has highlighted the variable response of AC in different topographical regions of meniscectomized joints to the altered mechanical stresses introduced by this surgical procedure. The AC at the joint margins, while thicker and richer in PG, was found to be biomechanically softer (lower shear modulus) than normal AC, and because of this, would be expected to undergo degenerative changes with time leading to the onset of OA.     

Septal replacement for severe anterior septal deviation

PURPOSE: To introduce a novel surgical technique for treatment of severe anterior septal deviation. MATERIALS AND METHODS: Retrospective case series set in a tertiary-care hospital. Ten patients were treated over an 18-month period. External septorhinoplasty and septal replacement for severe anterior septal deviation. Postoperative clinical nasal examination and photographic comparison. RESULTS: Ten patients were treated with septal replacement for severe anterior septal deviation over an 18-month period. All patients were followed for a minimum of 1 year. No postoperative complications were seen. All patients reported a subjective improvement in their nasal airway and nasal appearance. This was confirmed with clinical examination and photographic comparison. CONCLUSION: Septal replacement for severe anterior septal deviation is a viable option for select patients who can not be successfully treated with conventional techniques.