a-Amylases (a-1,4-glucan-4-glucanohydrolases) are a group of glycoside hydrolases that are widely distributed in bacteria, fungi, plants, and animal tissues [1,2]. They catalyze the hydrolysis of the a-(1,4) glycosidic linkage found in starch components and other related polysaccharides. a-Amylases are among the oldest known enzymes, but detailed information about their structure and inhibition started to become available only in the 1990s, as they became targets for regulation of important physiological processes. A promising field of current research involves suppression of the development of insect pests via impairment of their amylolytic digestion by naturally occurring a-amylase inhibitors. The proteinaceous a-amylase inhibitors are produced in plant tissues, in which they act as defensive proteins directed against exogenous digestive The digestive tract of lepidopteran insects is extremely alkaline. In the present work, molecular adaptation of amylolytic enzymes to this environment was investigated in the flour moth Ephestia kuehniella, an important stored-product pest. Three digestive a-amylases [Ephestia kuehniella a-amylase isoenzymes 1-3 (EkAmy1-3)] with an alkaline pH optimum were purified from larvae and biochemically characterized. These isoenzymes differ significantly in their sensitivity to a-amylase inhibitors of plant origin that are directed against herbivores as antifeedants. Such functional variability renders the amylolytic system less vulnerable to suppression by plant defensive molecules. Moreover, we found that expression of a-amylases is upregulated in larvae feeding on a diet enriched with an a-amylase inhibitor. The a-amylases are secreted into the larval midgut by an exocytotic mechanism, as revealed by immunogold microscopy. The cDNA sequence of EkAmy3 was determined, and a homology model of EkAmy3 was built in order to analyze the structural features responsible for adaptation to alkaline pH. First, the overall fold was found to be stabilized by remodeling of ion pairs. Second, molecular simulations supported by activity measurements showed that EkAmy3 does not bind a Cl -, owing to an Arg-to-Gln mutation in a conserved binding site. The Cl --binding residues are in contact with the catalytic residues, and this change might help to fine-tune the catalytic pK a values to an alkaline pH optimum. We conclude that lepidopteran a-amylases are evolutionarily adapted in terms of structure and expression dynamics for effective functioning in the digestive system. Abbreviations EkAmy1-3, Ephestia kuehniella a-amylase isoenzymes 1-3; HPA, human pancreatic a-amylase; PPA, porcine pancreatic a-amylase; qPCR, quantitative real-time RT-PCR; TMA, Tenebrio molitor a-amylase.
Colletotrichum acutatum J. H. Simmond is the causal agent of anthracnose rot and strawberry blackspot. This pathogen is listed by the EPPO as a regulated (formerly quarantined) organism for all European countries and is widely distributed throughout Europe (e.g., the United Kingdom, France, and Germany) (2). In the autumn of 2005, typical symptoms of anthracnose caused by C. acutatum (circular, dark, and sunken spots on fruit, dark, sunken lesions on petioles, and withering of the leaf, buds, and flowers) were repeatedly observed on field-grown strawberry plants in the Mělník Region of central Bohemia and Břeclav Region in southern Moravia, Czech Republic. Strawberry fruits and petioles showing typical symptoms were surface sterilized (30 s in 70% ethanol, 1 min in 10% NaOCl, and 15 s in 70% ethanol), rinsed in sterile water, dissected under aseptic conditions, and plated on 2% malt extract agar or placed in wet chambers and incubated at room temperature (18 to 20°C) for 10 days. All isolated strains were independently identified by morphological characteristics, plate-trapped antigen enzyme-linked immunosorbent assay (PTA-ELISA) (1), and PCR with the C. acutatum-specific primers ITS4 and CaInt2 (3). Morphological studies of C. acutatum were carried out on potato dextrose agar (4). The colonies were white, cream, grayish, or rose-orange before sporulation and the colony reverse was cream to orange with brown spots. The mycelial growth rate was 7.5 mm per day at 25°C. The conidia were one-celled, hyaline, cylindrical, 11.3 to 19.7 × 3.6 to 5.5 μm, and the majority of conidia were pointed at either or both ends. The appresoria were brown, globose to ellipsoidal, 5.0 to 7.5 × 5.0 to 6.2 μm, and the sclerotia were absent. Ten strawberry plants with green fruits of each cultivar Elsanta and Kama were sprayed with 500 ml of suspension of C. acutatum conidia (104 conidia per ml). This test was carried out in the glasshouse under quarantine conditions at 20 to 25°C. C. acutatum caused withering of the flowers or dark brown spots on green fruits on five plants of cv. Elsanta and on four plants of cv. Kama after a 6-week incubation period. Isolation and identification of the pathogen from the diseased tissues were done as described above. C. acutatum was reisolated from three fruits, four leaf blades, and four petioles from five plants of cv. Elsanta and four fruits, four leaf blades, and two petioles from four plants of cv. Kama. The fungus was not reisolated from the control strawberry plants. In three cases, the pathogen was detected in the crown of plants of cv. Elsanta by PCR and ELISA. References: (1) Anonymous. OEPP/EPPO Bull. 34:155, 2004. (2) I. M. Smith and L. M. F. Charles, eds. Distribution Maps of Quarantine Pests for the European Union and for the European and Mediterranean Plant Protection Organization. CABI Publishing, Wallingford, UK, 1998. (3) S. Sreenivasaprasad et al. Plant Pathol. 45:650, 1996. (4) P. Talhinhas et al. Phytopathology 92:986, 2002.
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