RESUMEN
BACKGROUND: Cystatins are inhibitors of cysteine proteases. The majority are only weak inhibitors of human cathepsin B, which has been associated with cancer, Alzheimer's disease and arthritis. RESULTS: Starting from the sequences of oryzacystatin-1 and canecystatin-1, a shuffling library was designed and a hybrid clone obtained, which presented higher inhibitory activity towards cathepsin B. This clone presented two unanticipated point mutations as well as an N-terminal deletion. Reversing each point mutation independently or both simultaneously abolishes the inhibitory activity towards cathepsin B. Homology modeling together with experimental studies of the reverse mutants revealed the likely molecular determinants of the improved inhibitory activity to be related to decreased protein stability. CONCLUSION: A combination of experimental approaches including gene shuffling, enzyme assays and reverse mutation allied to molecular modeling has shed light upon the unexpected inhibitory properties of certain cystatin mutants against Cathepsin B. We conclude that mutations disrupting the hydrophobic core of phytocystatins increase the flexibility of the N-terminus, leading to an increase in inhibitory activity. Such mutations need not affect the inhibitory site directly but may be observed distant from it and manifest their effects via an uncoupling of its three components as a result of increased protein flexibility.
Asunto(s)
Catepsina B/antagonistas & inhibidores , Cistatinas/genética , Cistatinas/farmacología , Barajamiento de ADN/métodos , Biblioteca de Genes , Modelos Moleculares , Secuencia de Aminoácidos , Clonación Molecular , Biología Computacional , Cartilla de ADN/genética , Electroforesis en Gel de Poliacrilamida , Humanos , Modelos Genéticos , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Mutación Puntual/genética , Reacción en Cadena de la Polimerasa , Alineación de Secuencia , Homología de SecuenciaRESUMEN
Using cDNA microarrays with 3800 cDNA fragments, we determined the expression profile of normal thyroid tissue, goiter, adenoma and papillary carcinoma (10 samples from each class). After background correction and statistical analysis, we identified a set of 160 genes as being differentially expressed in all pair-wise comparisons. Here we demonstrate that, at least on the basis of these differentially expressed genes, a positive correlation between goiter and papillary carcinomas could be observed. We identified a common set of genes whose expression is diminished in both goiter and papillary carcinomas as compared to normal thyroid tissue. Moreover, no genes with inverse correlation in samples from goiter and papillary carcinomas could be detected. Using Real-Time PCR and/or tissue microarrays, we confirmed the altered expression of some of the identified genes. Of notice, we demonstrate that the reduced mRNA levels of p27(kip1) observed in papillary carcinomas as compared to either goiter or normal thyroid tissues (P<0.001) is accompanied by an altered protein distribution within the cell. In papillary carcinomas, P27(KIP1) is preferentially cytoplasmic as opposed to goiter or normal thyroid tissue, where P27(KIP1) is preferentially located in the nucleus. The exploitation of the data presented here could contribute to the understanding of the molecular events related to thyroid diseases and gives support to the notion that common molecular events might be related to the frequent observation of areas of papillary carcinomas in the gland of patients with goiter.
Asunto(s)
Carcinoma Papilar/genética , Perfilación de la Expresión Génica , Bocio/genética , Glándula Tiroides/metabolismo , Neoplasias de la Tiroides/genética , Proteínas Portadoras/análisis , Inhibidor p27 de las Quinasas Dependientes de la Ciclina , Humanos , Péptidos y Proteínas de Señalización Intracelular/análisis , Análisis de Secuencia por Matrices de Oligonucleótidos , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Análisis de Matrices TisularesRESUMEN
Sugarcane is an important crop that has recently become subject to attacks from the weevil Sphenophorus levis, which is not efficiently controlled with chemical insecticides. This demands the development of new control devices for which digestive physiology data are needed. In the present study, ion-exchange chromatography of S. levis whole midgut homogenates, together with enzyme assays with natural and synthetic substrates and specific inhibitors, demonstrated that a cysteine proteinase is a major proteinase, trypsin is a minor one and chymotrypsin is probably negligible. Amylase, maltase and the cysteine proteinase occur in the gut contents and decrease throughout the midgut; trypsin is constant in the entire midgut, whereas a membrane-bound aminopeptidase predominates in the posterior midgut. The cysteine proteinase was purified to homogeneity through ion-exchange chromatography. The purified enzyme had a mass of 37 kDa and was able to hydrolyze Z-Phe-Arg-MCA and Z-Leu-Arg-MCA with k(cat)/K(m) values of 20.0±1.1 µM(-1)s(-1) and 30.0±0.5 µM(-1)s(-1), respectively, but not Z-Arg-Arg-MCA. The combined results suggest that protein digestion starts in the anterior midgut under the action of a cathepsin L-like proteinase and ends on the surface of posterior midgut cells. All starch digestion takes place in anterior midgut. These data will be instrumental to developing S. levis-resistant sugarcane.