Cloning and Secondary Structure Analysis of Caleosin, a Unique Calcium- Binding Protein in Oil Bodies of Plant Seeds

  • Chen J
  • Tsai C
  • Tzen J
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Plant seed oil bodies comprise a matrix of triacyl-glycerols surrounded by a monolayer of phospholipids embedded with abundant oleosins and some minor pro-teins. Three minor proteins, temporarily termed Sops 1-3, have been identified in sesame oil bodies. A cDNA se-quence of Sopl was obtained by PCR cloning using degenerate primers derived from two partial amino acid sequences, and subsequently confirmed via immunologi-cal recognition of its over-expressed protein in Escheri-chia coli. Alignment with four published homologous sequences suggests Sopl as a putative calcium-binding pro-tein. Immunological cross-recognition implies that this protein, tentatively named caleosin, exists in diverse seed oil bodies. Caleosin migrated faster in SDS-PAGE when incubated with Ca 2+ . A single copy of caleosin gene was found in sesame genome based on Southern hybridization. Northern hybridization revealed that both caleosin and oleosin genes were concurrently transcribed in maturing seeds where oil bodies are actively assembled. Hydropathy plot and secondary structure analysis suggest that caleosin comprises three structural domains, i.e., an N-terminal hydrophilic calcium-binding domain, a central hydropho-bic anchoring domain, and a C-terminal hydrophilic phos-phorylation domain. Compared with oleosin, a conserved proline knot-like motif is located in the central hydropho-bic domain of caleosin and assumed to involve in protein assembly onto oil bodies.

Author-supplied keywords

  • Caleosin —
  • Oil body —
  • Proline knot —
  • Seed —
  • Sesame

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  • Jeff C F Chen

  • Corinne C Y Tsai

  • Jason T C Tzen

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