Purificação e caracterização de inibidores de tripsina de sementes de Pithecellobium dumosun e seus efeitos

Abstract

Five Kunitz-type trypsin inhibitors (JB1, JB2, JB3-1, JB3-2 and JB4) were purified from Pithecellobium dumosum seeds, a tree of the sub-family Mimosoideae, by TCA precipitation, affinity chromatography on immobilized trypsin-Sepharose and reverse phase HPLC using Vydac C-18 column. The five inhibitors had Mr between 18 and 20 kDa with a single polypeptide chain as determined by SDS-PAGE with and without reduction. JB1, JB3-1 and JB3-2 had Mr of 19.70, 19.69 and 19.69 kDa, respectively, by MALDI-TOF. JB2 and JB4 had Mr of 18.08 and 20.85, respectively, by SDS-PAGE. The N-terminal sequences of JB1, JB3-1 and JB3-2 showed identity with others Kunitz-type inhibitors. The five inhibitors were stable over a wide range of temperature and pH. The inhibition of trypsin by JB1, JB2 and JB4 was competitive. JB1, JB2, JB3-1 and JB3-2 showed Ki values of 3.56 x 10-8 M, 1.65 x 10-8 M, 4.20 x 10-8 M, 2.88 x 10-8 M, respectively, against bovine trypsin. In comparison with others inhibitors JB4, with Ki of 5.70 x 10-10 M, showed a high affinity toward trypsin. Among the inhibitors purified only JB4 inhibited chymotrypsin activity. The activities of elastase and bromelain were not inhibited for these inhibitors. The inhibition of JB1, JB2, JB3-1 and JB3-2 on papain varied between 32.93 to 48.82% of inhibition and was indicative of its bifunctionality with exception of JB4 that inhibited this activity in 9.9%. The papain inhibition by JB1 and JB2 were noncompetitive type and the Kivalues were 7.6 x 10-7 and 5.1 x 10-7 M, respectively. In vitro assays against digestive proteinases from Lepidoptera, Diptera and Coleoptera pests were carried out. These inhibitors were effective towards trypsin-like digestive enzymes of the insect in different degrees. The digestive enzymes from Zabrotes subfasciatus and Ceratitis capitata were inhibited by JB1 in 68.87 and 65.53% respectively, and Callosobruchus maculatus, Alabama argillaceae and Plodia intepunctella enzymes were inhibited in the range of 29.18 to 44.35%. Digestive enzymes from Z. subfasciatus, C. maculatus and C. capitata were inhibited by JB2 in the range of 70.04 to 74.54%, and the enzymes of A. argillaceae and P. intepunctella were suppressed in 13.58 and 48.67%, respectively. Trypsin-like activities of larval from Z. subfasciatus were suppressed in 67.33 and 56.93% by JB3-1 and JB3-2, respectively, and the activities of C. maculatus, A. argillaceae, P. intepunctella and C. capitata were inhibited by these inhibitors in the range of 5.17-49.00%. JB4 inhibited around 54.53 to 66.15% the digestive enzymes of C. maculatus, Z. subfasciatus and A. argillaceae and the digestive enzymes from P. intepunctella and C. capitata larvae in 8.97% and 37.47%, respectively. The inhibition of trypsin-like and papain-like proteinases of several insects suggested that these inhibitors may affect the growth and survival of these insect pests when incorporated into artificial diet and their bifunctionality are indicative that these inhibitors could be strong candidates to plant management programs cross transgenia.