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Positively charged DNA-binding proteins cause apparent cell membrane translocation.
Mathias Lundberg1, Magnus Johansson
1Medical Nobel Institute for Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institute, Stockholm, Sweden.
Biochemical and Biophysical Research Communications
|February 16, 2002
Summary
Positively charged proteins like histone H1 may not cross cell membranes in living cells. Their nuclear accumulation observed in studies might be a fixation artifact, not true cell membrane translocation.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Positively charged DNA-binding proteins, including viral (HIV Tat, HSV VP22) and homeobox (Antennapedia) proteins, are reported to cross cell membranes.
- The mechanism for this apparent translocation is poorly understood and suggested to be receptor- and energy-independent.
Purpose of the Study:
- To investigate the mechanism of cell membrane translocation for positively charged proteins.
- To determine if observed nuclear accumulation in previous studies reflects true translocation in living cells or an artifact.
Main Methods:
- Studied the adherence and removal of positively charged proteins (VP22, histone H1) from living cell membranes.
- Examined protein localization in cells before and after fixation procedures.
Main Results:
- Positively charged proteins (VP22, histone H1) adhered to living cell membranes but were removable with washing.
- After fixation, these proteins relocated to the cell nucleus, suggesting an artifact.
- The majority of studies on "membrane permeable" proteins utilize fixation techniques.
Conclusions:
- Observed nuclear accumulation of positively charged proteins like VP22 and histone H1 may be due to fixation artifacts.
- Apparent cell membrane translocation of these proteins might occur during the fixation process, not in living cells.