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Structural Analysis of an Echinococcus granulosus Actin-Fragmenting Protein by Small-Angle X-Ray Scattering Studies and Molecular Modeling

Eliana D. Grimm ^*, Rodrigo V. Portugal , Mário de Oliveira Neto , Nádia H. Martins , Igor Polikarpov , Arnaldo Zaha ^*  and Henrique B. Ferreira ^* 

^* Laboratório de Biologia Molecular de Cestódeos, Centro de Biotecnologia, and Departamento de Biologia Molecular e Biotecnologia, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Porto Alegre RS, Brazil; and Grupo de Cristalografia, Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos SP, Brazil

Correspondence: Address reprint requests to Dr. Henrique B. Ferreira, Laboratório de Biologia Molecular de Cestódeos, Centro de Biotecnologia, UFRGS, Caixa Postal 15005, Porto Alegre RS 91501-970, Brazil. Tel.: 55-51-33167768; Fax: 55-51-33167309; E-mail: henrique{at}cbiot.ufrgs.br.

The Echinococcus granulosus actin filament-fragmenting protein (EgAFFP) is a three domain member of the gelsolin family of proteins, which is antigenic to human hosts. These proteins, formed by three or six conserved domains, are involved in the dynamic rearrangements of the cytoskeleton, being responsible for severing and capping actin filaments and promoting nucleation of actin monomers. Various structures of six domain gelsolin-related proteins have been investigated, but little information on the structure of three domain members is available. In this work, the solution structure of the three domain EgAFFP has been investigated through small-angle x-ray scattering (SAXS) studies. EgAFFP exhibits an elongated molecular shape. The radius of gyration and the maximum dimension obtained by SAXS were, respectively, 2.52 ± 0.01 nm and 8.00 ± 1.00 nm, both in the absence and presence of Ca²⁺. Two different molecular homology models were built for EgAFFP, but only one was validated through SAXS studies. The predicted structure for EgAFFP consists of three repeats of a central ß-sheet sandwiched between one short and one long -helix. Possible implications of the structure of EgAFFP upon actin binding are discussed.