MBE Advance Access published online on August 14, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn180
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Research Article |
Evolution of genes and repeats in the Nimrod superfamily Research article
1 Institute of Genetics, Biological Research Center of the Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged, Hungary
2 Department of Ecology, University of Szeged, Egyetem street 2., H-6721 Szeged, Hungary
3 Umea Centre for Molecular Pathogenesis, By. 6L, Umea University, S-901 87 Umea, Sweden
Corresponding author: Kálmán Somogyi, Institute of Genetics, Biological Research Center of the Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged, Hungary, Phone: +36-62-599-622, Fax: +36-62-433-503, E-mail: somogyi{at}brc.hu
Received for publication March 13, 2008. Revision received May 5, 2008. Revision received July 4, 2008. Revision received July 30, 2008. Accepted for publication August 5, 2008.
The recently identified Nimrod superfamily is characterized by the presence of a special type of EGF repeat, the NIM repeat, located right after a typical CCXGY/W amino acid motif. On the basis of structural features nimrod genes can be divided into three types. The proteins encoded by Draper-type genes have an EMI domain at the N-terminal part and only one copy of the NIM motif, followed by a variable number of EGF-like repeats. The products of Nimrod B-type and Nimrod C-type genes (including the eater gene) have different kinds of N-terminal domains, lack EGF-like repeats but contain a variable number of NIM repeats. Draper and Nimrod C-type (but not Nimrod B-type) proteins carry a transmembrane domain.
Several members of the superfamily were claimed to function as receptors in phagocytosis and/or binding of bacteria, which indicates an important role in the cellular immunity and the elimination of apoptotic cells. In this paper the evolution of the Nimrod superfamily is studied with various methods on the level of genes and repeats. A hypothesis is presented in which the NIM repeat, along with the EMI domain, emerged by structural reorganizations at the end of an EGF-like repeat chain, suggesting a mechanism for the formation of novel types of repeats. The analyses revealed diverse evolutionary patterns in the sequences containing multiple NIM repeats. While in the Nimrod B and Nimrod C proteins show characteristics of independent evolution, many internal NIM repeats in Eater sequences seem to have undergone concerted evolution. An analysis of the nimrod genes has been performed using phylogenetic and other methods and an evolutionary scenario of the origin and diversification of the Nimrod superfamily is proposed.
Our study presents an intriguing example how the evolution of multigene families may contribute to the complexity of the innate immune response.
Key Words: gene family • concerted evolution • birth-and-death evolution • repeat evolution • innate immunity • insect • Drosophila
KS: somogyi{at}brc.hu; BS: sbotond{at}gmail.com; ZP: penzes{at}bio.u-szeged.hu; ÉK: kurucz{at}brc.hu; JZ: zsamboki{at}brc.hu; DH: dan.hultmark{at}ucmp.umu.se; IA: ando{at}brc.hu.