Mannan-hydrolysis by hemicellulases: enzyme-polysaccharide interaction of a modular beta-mannanase

The enzymatic degradation of plant polysaccharides is a process of fundamental importance in nature which involves a wide range of enzymes. In this work, the structure and function of hemicellulose-degrading enzymes was investigated. The focus was on a beta-mannanase (TrMan5A) produced by the filamentous fungus Trichoderma reesei. This enzyme is composed of a catalytic module and a carbohydrate-binding module (CBM). In this thesis, the enzyme-polysaccharide interaction in both these modules was investigated. The results demonstrate that the CBM of TrMan5A is important for hydrolysis of complex mannan substrates containing cellulose. Furthermore, the increase in activity could be linked to binding of the CBM to the complex substrate. Binding studies revealed that the CBM binds to cellulose, but not to mannan. Studies of the enzyme/polysaccharide interaction in the active site cleft of the catalytic module of TrMan5A showed that a mutant of Arg 171 displayed activity in the same range as the wild-type enzyme toward polymeric substrates. However, the Arg171 mutant was impaired in hydrolysis of small substrates. Interestingly, this mutant also appears to have a more alkaline activity pH-optimum than the wild-type. The low or abolished activity observed with mutants of the predicted catalytic glutamates (Glu169 and Glu276) support their importance in hydrolysis. In addition to TrMan5A, the properties of a beta-mannanase (MeMan5A) from blue mussel and a beta-mannosidase (AnMan2A) from Aspergillus niger, were studied in this work. Investigations on the catalytic properties of the enzymes showed that all three enzymes are capable of degrading polymeric mannan. Furthermore, analysis by transmission electron microscopy revealed that TrMan5A and AnMan2A degrades highly crystalline mannan. Degradation of glucomannan and galactoglucomannan by several polysaccharide-degrading enzymes shows that these substrates can be hydrolysed by both mannoside- and glucoside-hydrolases. Furthermore, the results presented show that cellulases potentially are able to hydrolyse other components in the plant cell wall. Altogether, the results presented demonstrates the need to use complex substrates in order to reveal the mechanisms of plant polysaccharide degradation. In conclusion, this work has shown that the enzyme/polysaccharide interaction in the two modules of TrMan5A is important in determining the overall enzymatic activity and specificity

Early interventions and disability insurance: Experience from a field experiment

This paper estimates the effects of early interventions in the Swedish sickness insurance system. The aim of the interventions is to screen and, further to, rehabilitate sick listed individuals. We find that the early interventions - in contrast to what is expected - increase the inflow into disability benefits by around 20 percent. In order to explain the results, we develop a simple theoretical model based on asymmetric information of the health status. The model predicts that the treatment effect is larger for individuals with low incentives to return to work. In order to test this prediction we estimate effects for sick listed employed and unemployed separately. Consistent with the model's prediction, we find that the effect is larger for the unemployed than for the employed

Early interventions and disability insurance: Experience from a field experiment

This paper estimates the effects of early interventions in the Swedish sickness insurance system. The aim of the interventions is to screen and, further to, rehabilitate sick listed individuals. We find that the early interventions - in contrast to what is expected - increase the inflow into disability benefits by around 20 percent. In order to explain the results, we develop a simple theoretical model based on asymmetric information of the health status. The model predicts that the treatment effect is larger for individuals with low incentives to return to work. In order to test this prediction we estimate effects for sick listed employed and unemployed separately. Consistent with the model's prediction, we find that the effect is larger for the unemployed than for the employed

Relations Between Control Signal Properties and Robustness Measures

In this paper we consider control signal properties, such as maximum magnitude and activity, as well as system robustness measures. We derive an ideal controller and control signal for exponential disturbance rejection for a first order process with time delay. For the resulting closed-loop system, it is shown analytically that there are strong interconnections between robustness measures and control signal properties regarding load disturbance attenuation. The results imply that popular controller design methods implicitly take control signal properties into consideration

Rehabilitation of mental illness and chronic pain: The impact on sick leave and health

This paper exploits a government initiative to analyze the effect of cognitive behavioral therapy (CBT) for individuals with mild or moderate mental illness and multidisciplinary treatment (MDT) for individuals with pain in back and shoulders. We employ a propensity score matching approach to study the effects on sick leave, health care consumption and drug prescriptions. We find that CBT improved health and prevented sick leave for individuals who were not on sick leave when treatment was initiated but had no effect for individuals who were on sick leave when the treatment was initiated. MDT was a failure regardless of the individual's sick leave status at the time of treatment. MDT increased sick leave while having no long term impact on either health care visits or drug prescriptions

Structure of Hordeum vulgare NADPH-dependent thioredoxin reductase 2. Unwinding the reaction mechanism

Thioredoxins (Trxs) are protein disulfide reductases that regulate the intracellular redox environment and are important for seed germination in plants. Trxs are in turn regulated by NADPH-dependent thioredoxin reductases (NTRs), which provide reducing equivalents to Trx using NADPH to recycle Trxs to the active form. Here, the first crystal structure of a cereal NTR, HvNTR2 from Hordeum vulgare (barley), is presented, which is also the first structure of a monocot plant NTR. The structure was determined at 2.6 Å resolution and refined to an R (cryst) of 19.0% and an R (free) of 23.8%. The dimeric protein is structurally similar to the structures of AtNTR-B from Arabidopsis thaliana and other known low-molecular-weight NTRs. However, the relative position of the two NTR cofactor-binding domains, the FAD and the NADPH domains, is not the same. The NADPH domain is rotated by 25° and bent by a 38% closure relative to the FAD domain in comparison with AtNTR-B. The structure may represent an intermediate between the two conformations described pre­viously: the flavin-oxidizing (FO) and the flavin-reducing (FR) conformations. Here, analysis of interdomain contacts as well as phylogenetic studies lead to the proposal of a new reaction scheme in which NTR–Trx interactions mediate the FO to FR transformation