Ciliate pellicular proteome identifies novel protein families with characteristic repeat motifs that are common to Alveolates

Mol Biol Evol. 2010 Dec 2. [Epub ahead of print]

Ciliate pellicular proteome identifies novel protein families with characteristic repeat motifs that are common to Alveolates

Gould SB, Kraft LG, van Dooren GG, Goodman CD, Ford KL, Cassin AM, Bacic A, McFadden GI, Waller RF.

School of Botany, University of Melbourne, 3010 Victoria, Australia.

Abstract
The pellicles of alveolates (ciliates, apicomplexans and dinoflagellates) share a common organization, yet perform very divergent functions including motility, host cell invasion and armor. The alveolate pellicle consists of a system of flattened membrane sacs (alveoli, which are the defining feature of the group) below the plasma-membrane that is supported by a membrane skeleton as well as a network of microtubules and other filamentous elements. We recently showed that a family of proteins, alveolins, are common and unique to this pellicular structure in alveolates. To identify additional proteins that contribute to this structure, a pellicle proteome study was conducted for the ciliate Tetrahymena thermophila. We found 1173 proteins associated with this structure, 45% (529 proteins) of which represented novel proteins without matches to other functionally characterized proteins. Expression of four newly identified T. thermophila pellicular proteins as GFP-fusion proteins confirmed pellicular location, and one new protein located in the oral apparatus. Bioinformatic analysis revealed that 21% of the putative pellicular proteins, predominantly the novel proteins, contained highly repetitive regions with strong amino acid biases for particular residues (K, E, Q, L, I & V). When the T. thermophila novel proteins were compared to apicomplexan genomic data, 278 proteins with high sequence similarity were identified, suggesting that many of these putative pellicular components are shared between the alveolates. Of these shared proteins, 126 contained the distinctive repeat regions. Localization of two such proteins in Toxoplasma gondii confirmed their role in the pellicle, and in doing so identified two new proteins of the apicomplexan invasive structure - the apical complex. Screening broadly for these repetitive domains in genomic data revealed large and actively evolving families of such proteins in alveolates, suggesting that these proteins might underpin the diversity and utility of their unique pellicular structure.

PMID: 21127172 [PubMed - as supplied by publisher]