Sadaki Yokota

Publications (3)4.74 Total impact

• Article: Low pH facilitates uptake of proteins by cells through a non-endocytic pathway.

  Mitsuyoshi Motizuki, Toshiaki Takei, Kachio Tasaka, Sadaki Yokota, Shuichi Kojima, Tatsuya Haga, Kunio Tsurugi
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  ABSTRACT: We previously noted that bovine apolipoprotein A-II (apoA-II) had a bactericidal effect causing morphological changes in the cytoplasm. To determine whether and how apoA-II and apoA-I, which have acidic isoelectric points (pIs), enter cells, we determined the rates of uptake of FITC-labeled proteins by fibroblast cells and found that they entered cells more easily at low pH than at neutral pH under conditions where endocytosis was inhibited. The enhanced uptake of proteins at low pH was also observed for other proteins examined regardless of the molecular weight (M(r)) or pI in a time-dependent manner, although the efficiency of uptake varied among the proteins. Furthermore, a pH gradient was shown to be the main driving force for the translocation. As cells were viable above pH 4 for 2 h at 4 degrees C and internalized beta-galactosidase was active under these conditions, we suggest that this procedure is applicable to the injection of proteins into cells without the use of an apparatus such as a microinjector.
  Journal of Biochemistry 07/2004; 135(6):713-9. · 2.37 Impact Factor
• Article: Structure-activity analysis of an antimicrobial peptide derived from bovine apolipoprotein A-II.

  Mitsuyoshi Motizuki, Takanori Satoh, Toshiaki Takei, Takehito Itoh, Sadaki Yokota, Shuichi Kojima, Kin-ichiro Miura, Tatsuya Samejima, Kunio Tsurugi
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  ABSTRACT: We previously showed that bovine apolipoprotein A-II (apoA-II) has antimicrobial activity against Escherichia coli in PBS, and its C-terminal residues 49-76 are responsible for the activity using synthetic peptides. In order to understand the structural requirements of peptide 49-76 for the antimicrobial activity, the N- or C-terminus was truncated and then the charged (Lys or Asp) or Ser residues were replaced by Ala. Deletion of the first or last three amino acids and replacement of Lys-54/55 or 71/72 by Ala caused a substantial decreases in alpha-helical content in 50% TFE, showing the possible presence of helices in N- and C-terminal regions, respectively. The anti-Escherichia coli activity of the peptide correlated with its liposome-binding activity. Replacement of Lys-54/55 or 71/72 by Ala resulted in an almost complete loss of anti-E. coli activity with a substantial decrease in liposome-binding activity. Moreover, deletion of the last three amino acids caused a reduction to 1/17 of the original anti-E. coli activity with a moderate decrease in liposome-binding activity. In contrast, replacement of Ser-65/66, Asp-59, or Asp-69 by Ala hardly affected the anti-E. coli activity. These findings suggest that Lys-54/55 and Lys-71/72 on the putative helices are critical for antimicrobial activity, and the C-terminal 3 amino acids are important for the structural integrity of the C-terminal region for effective antimicrobial activity.
  Journal of Biochemistry 08/2002; 132(1):115-9. · 2.37 Impact Factor
• Article: Characterization of a Novel Acidic Protein of 38 kDa, A0, in Yeast Ribosomes Which Immunologically Cross-Reacts with the 13 kDa Acidic Ribosomal Proteins, A1/A2

  Kazuhiro Mitsui, Mitsuyoshi Motizuki, Yaeta ENDO, Sadaki Yokota, Kunio Tsurugi
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  ABSTRACT: A new ribosomal protein of 38 kDa, named A0, was detected in yeast ribosomes on immunoblotting. The antibody used here was that against A1/A2, 13 kDa acidic ribosomal proteins which cross-reacted with A0. Although A0 and A1/A2 share common antigenic determinants, they differ in the following biochemical properties. While A1/A2 could be extracted from ribosomes with ethanol and ammonium sulfate, A0 could not. A0 gave two protein spots in a less acidic region than for A1/A2 on two-dimensional gel electrophoresis. The heterogeneity observed for A0 was ascribable to phosphorylation because one spot disappeared after treatment of the ribosomes with phosphatase. The syntheses of A0 and A1/A2 are directed by different mRNA species, as judged with a cell-free translation system, ruling out the possibility that A0 is a precursor of A1/A2. Although a mammalian ribosomal protein equivalent to A0 has been shown to be associated with 13 kDa acidic proteins in the cytoplasm, essentially no A0 was detected on immunoblotting in the yeast cytosol, while a small but detectable amount of A1/A2 was present. The possibility that A0 is a eukaryotic equivalent of L10 of Escherichia coli is discussed.