Related Experiment Videos
Isolation, characterisation and growth-related changes of an HMG-like protein from microplasmodia of Physarum
1Biophysics Section, School of Biological Sciences, Portsmouth Polytechnic, U.K.
Abstract:
An alanine, lysine and glutamic acid-rich nuclear protein (P2) of Mr approximately 19,500 co-extracts with the histones from nuclei of Physarum polycephalum when using the CaCl2 method for histone extraction [1] and was found to have the composition previously ascribed to a putative histone H1(0) isolated from microplasmodia using 5% PCA (Yasuda, H., Mueller, R.D., Logan, K.A. and Bradbury, E.M. (1986) J. Biol. Chem. 261, 2349-2354). P2 has very similar electrophoretic properties to chicken erythrocyte histone H5, calf thymus histone H1(0) and the Physarum HMG-like protein AS-2, but does not appear to be immunologically or structurally similar to H5 or H1(0). An increase in the abundance of P2 was observed during exponential growth in microplasmodia, reaching an approximately 1:1 ratio with histone H1 by 48 h of culture. Standard amino acid analysis and NMR show that P2 is more HMG-like than H1-like and CD measurements demonstrated that P2 contains only 5% secondary structure in its maximally structured state and is, therefore, essentially unstructured under in vivo conditions. Also possible clustering of acidic residues is detected using CD and may be of functional significance. Analysis of post-translational modification of P2 shows that it is phosphorylated at up to three sites as isolated from immature spherules. The relationship of P2 to the HMG family of proteins and AS-2 is discussed.
Insights
A nuclear protein (P2) in Physarum polycephalum, rich in alanine, lysine, and glutamic acid, shows characteristics similar to High Mobility Group (HMG) proteins. This protein is unstructured in vivo and undergoes phosphorylation, suggesting a potential role in cellular processes.
Area of Science:
- Molecular Biology
- Biochemistry
- Cell Biology
Background:
- A nuclear protein, designated P2, was co-extracted with histones from Physarum polycephalum.
- P2 shares compositional and electrophoretic similarities with histone H1(0) and HMG-like protein AS-2.
Purpose of the Study:
- To characterize the biochemical and structural properties of the nuclear protein P2.
- To investigate the relationship of P2 to histone H1 and the High Mobility Group (HMG) protein family.
Main Methods:
- Histone extraction using the CaCl2 method.
- Electrophoresis, amino acid analysis, Nuclear Magnetic Resonance (NMR), and Circular Dichroism (CD) spectroscopy.
- Analysis of post-translational modifications, specifically phosphorylation.
Main Results:
- P2 exhibits an amino acid composition more akin to HMG proteins than histones.
- CD measurements indicate P2 is largely unstructured under physiological conditions, with potential acidic residue clustering.
- P2 is phosphorylated at multiple sites and its abundance increases during exponential growth.
Conclusions:
- P2 is an HMG-like nuclear protein in Physarum polycephalum.
- Its unstructured nature and phosphorylation suggest a dynamic functional role.
- Further investigation into P2's relationship with HMG proteins and AS-2 is warranted.