RESUMO
L27 domain, initially identified in the Caenorhabditis elegans Lin-2 and Lin-7 proteins, is a protein interaction module that exists in a large family of scaffold proteins. The domain can function as an organization center of large protein assemblies required for establishment and maintenance of cell polarity. We have solved the high-resolution NMR structure of a tetrameric complex of L27 domains containing two SAP97-mLin-2 L27 domain heterodimers. Each L27 domain contains three a-helices. The first two helices of each domain are packed together to form a four-helical bundle in the heterodimer. The third helix of each L27 domain forms another four-helical bundle that assembles the two heterodimers into a tetramer. The structure of the complex provides a mechanistic explanation for L27 domain-mediated polymerization of scaffold proteins, a process that is crucial for the assembly of supramolecular complexes in asymmetric cells.
Assuntos
Biopolímeros/química , Proteínas de Caenorhabditis elegans/química , Caenorhabditis elegans/química , Proteínas de Helminto/química , Proteínas de Membrana/química , Sequência de Aminoácidos , Animais , Cromatografia em Gel , Humanos , Camundongos , Dados de Sequência Molecular , Homologia de Sequência de AminoácidosRESUMO
Tachycitin is an invertebrate chitin-binding protein with an amidated C-terminus, and possesses antimicrobial activity against both fungi and bacteria. The (1)H-NMR-based tertiary structure of tachycitin was recently determined [Suetake et al. (2000) J. Biol. Chem., 275, 17929-17932]. In order to examine the structural and functional features of tachycitin more closely, we performed for the first time, gene expression, refolding, (15)N-NMR-based characterizations, and antimicrobial activity measurements of a recombinant tachycitin (rTcn) that does not have the amide group at the C-terminus. The NMR analysis indicated that rTcn possesses the same structural construction as the native tachycitin. The backbone (15)N relaxation measurements showed that the molecular motional correlation time of rTcn increases as its concentration increases, indicating that tachycitins have a tendency to aggregate with each other. rTcn exhibits antimicrobial activity against fungi but not against bacteria. The cell surface of fungi contains chitin as an essential constituent, but that of bacteria does not. These results suggest that not only the chitin-binding region but also the C-terminal amide group of tachycitin plays a significant role in its antimicrobial properties.
