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Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
Published on: September 26, 2016
Mistic: cellular localization, solution behavior, polymerization, and fibril formation
Hay Dvir1, Matthew E Lundberg, Samir K Maji
1Structural Biology Laboratory, The Salk Institute for Biological Studies, San Diego, California 92037, USA.
Abstract:
Mistic represents a family of unique membrane-associating proteins originally found in Bacillus subtilis (M110). As a fusion partner, it has been shown to assist overexpression of foreign integral membrane proteins in E. coli. We have expressed shorter Mistic homologs from other Bacillus species and surprisingly, unlike M110, found them abundant in the cytoplasm. These Mistic homologs including the corresponding shorter sequence (amino acids 27 through 110 of M110) exist as multimeric assemblies in solution in the absence of detergent. Crystals of Mistic from B. leicheniformis (M2) diffracted to 3.2 A resolution, indicating that it exists as a multimer in the crystalline state as well. Moreover, we show that although M2 is mostly alpha-helical, it tends to polymerize and form fibrils. Such oligomerization could potentially mask the charged surface of the monomeric Mistic to assist membrane integration.
Insights
New Mistic protein homologs from Bacillus species are found in the cytoplasm and form multimeric assemblies. This oligomerization may aid in membrane integration by masking charged surfaces.
Area of Science:
- Microbiology
- Structural Biology
- Protein Biochemistry
Background:
- Mistic proteins are unique membrane-associating proteins identified in Bacillus subtilis.
- Mistic aids in the overexpression of foreign integral membrane proteins when used as a fusion partner in E. coli.
Purpose of the Study:
- To investigate the localization and structural properties of Mistic homologs from other Bacillus species.
- To understand the oligomerization behavior of Mistic proteins and its potential role in membrane association.
Main Methods:
- Expression of shorter Mistic homologs from various Bacillus species.
- Analysis of protein localization (cytoplasmic vs. membrane-associated).
- Crystallization and X-ray diffraction of Mistic from B. leicheniformis (M2) to determine structure.
- Biophysical characterization of Mistic homologs in solution.
Main Results:
- Unlike the original Mistic from B. subtilis (M110), expressed Mistic homologs were predominantly found in the cytoplasm.
- These cytoplasmic Mistic homologs, including a specific shorter sequence (amino acids 27-110 of M110), form stable multimeric assemblies in solution without detergent.
- Crystallographic analysis of Mistic from B. leicheniformis (M2) confirmed its multimeric state and revealed an alpha-helical structure.
- Mistic M2 exhibits a tendency to polymerize and form fibrils, suggesting an inherent oligomerization capability.
Conclusions:
- Mistic homologs from different Bacillus species exhibit distinct localization patterns, with some residing in the cytoplasm.
- The observed multimeric assembly and fibril formation of Mistic proteins in solution suggest a self-oligomerization mechanism.
- This oligomerization process might be crucial for Mistic's function, potentially by masking charged residues to facilitate membrane integration.
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