Plateins: A Novel Family of Signal Peptide‐Containing Articulins in Euplotid Ciliates¹

Abstract

In euplotid ciliates, the cortex is reinforced by alveolar plates--proteinaceous scales located within the membranous alveolar sacs, forming a monolayer just below the plasma membrane. This system appears to play a cytoskeletal role analogous to that provided by the fibrous epiplasm found beneath the cortical alveoli in other ciliates. In Euplotes aediculatus, the major alveolar plate proteins (termed alpha-, beta-, and gamma-plateins) have been identified. Using anti-platein antibodies, an expression library of Euplotes genes was screened, and a platein gene identified, cloned, and completely sequenced. Comparison of its derived amino acid sequence with microsequences obtained directly from purified plateins identified this gene as encoding one of the closely related beta- or gamma-plateins. The derived protein, of 644 amino acids (74.9 kDa), is very acidic (pI = 4.88). Microsequences from authentic alpha-platein were then used to design oligonucleotide primers, which yielded, via a PCR-based approach, the sequences of two alpha-platein genes from E. aediculatus. Even more acidic proteins, the derived alpha1- and alpha2-plateins contain 536 and 501 residues, respectively. Analyses of their amino acid sequences revealed the plateins to be members of the articulin superfamily of cytoskeletal proteins, first described in Euglena and now identified in the ciliate Pseudomicrothorax and in Plasmodium. The hallmark articulin repetitive motifs (based on degenerate valine- and proline-rich 12-mers) are present in all three plateins. In beta/gamma-platein this primary motif domain (27 repeats) is central in the molecule, whereas the primary repeats in the alpha-plateins lie near their C-termini. A cluster of proline-rich pentameric secondary repeats is found in the C-terminus of beta/gamma-platein, but near the N-terminus of alpha-plateins. All three plateins contain canonical N-terminal signal sequences, unique among known cytoskeletal proteins. The presence of start-transfer sequences correlates well with the final intra-alveolar location of these proteins. This feature, and significant differences from known articulins in amino acid usage and arrangement within the repeat domains, lead us to propose that the plateins comprise a new family of articulin-related proteins. Efforts to follow microscopically the assembly of plateins into new alveolar plates during pre-fission morphogenesis are underway.

Characterization of Tt ALV2, an Essential Charged Repeat Motif Protein of the Tetrahymena thermophila Membrane Skeleton

“…1A; see Fig. S2A) but similar to that of plateins-which are also CRMPs-from Euplotes aediculatus (21). Colabeling with tubulin demonstrates that TtALV2 is excluded from the circumciliary ring region and absent from the oral apparatus ( Fig.…”

Transcriptome analysis reveals unique metabolic features in the Cryptosporidium parvum Oocysts associated with environmental survival and stresses

“…Each group of transporters possessed both up- and down-regulated members, with the top up-regulated genes were predominantly ABC-type, ion, nutrient and nuclear transporters that were mostly resumed to near normal levels in 5 h. The highly down-regulated genes were predominantly vacuolar ATPase subunits that remained down-regulated in 5 h. The increased expressions of several oocyst wall proteins; articulin proteins that are known to be important in maintaining cell shapes in Euglena and ciliates [26,27], and mucin-like proteins suggestive of active repairing on some cell/oocyst surface molecules.…”

Spatial analysis of biomineralization associated gene expression from the mantle organ of the pearl oyster Pinctada maxima

“…Articulins are part of the membrane skeleton of eukaryotic cells stabilizing plasma membranes [45,46]. It is suggested that ESTs PM265 and PM269, function as plateins, a new family of articulins described by Kloetzel et al [47]. Plateins contain modified articulin core domains typical of secreted structural proteins as well as a novel predicted signal peptides detected in intra-alveolar sacs, an extracellular environment.…”