Spectroscopic characterization and structural modeling of prolamin from maize and pearl millet |
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Authors: | Milton?Roque?Bugs Lucimara?Aparecida?Forato Raquel?Kely?Bortoleto-Bugs Hannes?Fischer Yvonne?Primerano?Mascarenhas Richard?John?Ward Email author" target="_blank">Luiz?Alberto?ColnagoEmail author |
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Institution: | (1) Embrapa Instrumentação Agropecuária, Rua XV de novembro 1452, 13560-970 São Carlos, SP , Brazil;(2) Grupo de Cristalografia, Instituto de Física de São Carlos, Universidade de São Paulo, Av. Trabalhador Sãocarlense 400, 13566-590 São Carlos, SP , Brazil;(3) Instituto de Física, Universidade de São Paulo, Rua do Matão, Travessa R 187, Cidade Universitária, 05315-970 São Paulo, SP, Brazil;(4) Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes 3900, 14049-901 Ribeirão Preto, SP , Brazil |
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Abstract: | Biophysical methods and structural modeling techniques have been used to characterize the prolamins from maize (Zea mays) and pearl millet (Pennisetum americanum). The alcohol-soluble prolamin from maize, called zein, was extracted using a simple protocol and purified by gel filtration in a 70% ethanol solution. Two protein fractions were purified from seed extracts of pearl millet with molecular weights of 25.5 and 7 kDa, as estimated by SDS-PAGE. The high molecular weight protein corresponds to pennisetin, which has a high -helical content both in solution and the solid state, as demonstrated by circular dichroism and Fourier transform infrared spectra. Fluorescence spectroscopy of both fractions indicated changes in the tryptophan microenvironments with increasing water content of the buffer. Low-resolution envelopes of both fractions were retrieved by ab initio procedures from small-angle X-ray scattering data, which yielded maximum molecular dimensions of about 14 nm and 1 nm for pennisetin and the low molecular weight protein, respectively, and similar values were observed by dynamic light scattering experiments. Furthermore, 1H nuclear magnetic resonance spectra of zein and pennisetin do not show any signal below 0.9 ppm, which is compatible with more extended solution structures. The molecular models for zein and pennisetin in solution suggest that both proteins have an elongated molecular structure which is approximately a prolate ellipsoid composed of ribbons of folded -helical segments with a length of about 14 nm, resulting in a structure that permits efficient packing within the seed endosperm. |
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Keywords: | Pennisetin molecular model Zein molecular model Circular dichroism Dynamic light scattering Small-angle X-ray scattering |
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