We have examined the contribution to protein stability of an interaction involving a charged hydrogen bond from an arginyl side chain (Arg67) in the serine proteinase inhibitor chymotrypsin inhibitor 2 (CI-2), by replacing this side chain with an alanyl residue by protein engineering. Using nuclear magnetic resonance spectroscopy (NMR), we have examined the effect of this mutation on the hydrogen-deuterium exchange rates of several backbone amide protons in the native and engineered proteins at 50 degrees C. These exchange rates provide a localized probe at multiple discrete sites throughout the protein and from comparison of native and mutant exchange rates allow calculation of the difference in free energy of exchange (delta delta Gex) resulting from the mutation. The results show that for the majority of amides observed this mutation results in delta delta Gex of ca. 1.7 kcal mol-1 over the whole CI-2 molecule. However, for two relatively exposed amide protons the exchange rates are found to be far less perturbed, implying that local unfolding mechanisms predominate for these protons. Direct measurement of the stability of both proteins to denaturation by guanidinum hydrochloride shows that the interaction contributes 1.4 kcal mol-1 to the stability of the molecule. This value is comparable to those obtained from the NMR exchange measurements and indicates that the exchange processes reflect the differences in stability between the native and mutant proteins.(ABSTRACT TRUNCATED AT 250 WORDS)
Soil fertility has direct implications on the agricultural production scenarios of a region. Surface soil samples at 1 km grid were collected to assess the fertility status of Lakhimpur district (Assam) in North East India. Fertility parameters like soil organic carbon, available nitrogen, phosphorus, potassium, iron, manganese, zinc and copper were determined using standard analytical procedure. Spatial distribution maps of the soil parameters were generated using regularized spline method in ArcGIS 10.0. The average soil organic carbon content was 1.05% and the maximum area was under high availability status (78%). In the case of nitrogen, 57% of the area was under low availability status. In the case of available potassium and phosphorus, the areas under low availability status were 48% and 49% respectively. But for micronutrients, in general, the availability status was high except for zinc, which indicated that 40% of the area was under low availability. A methodology was developed to integrate the individual nutrient layers using a set of decision rules to identify the multinutrient deficient zones. The integrated map showed that 24% of the area had multiple nutrient deficiencies and fell under high priority zone that warrant immediate nutrient management interventions to mitigate the situation.
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