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Updated: Aug 15, 2026
Membrane-SPINE: A Biochemical Tool to Identify Protein-protein Interactions of Membrane Proteins In Vivo
Published on: November 7, 2013
Purification and characterization of spiralin, the main protein of the Spiroplasma citri membrane
H Wróblewski1, K E Johansson, S Hjérten
1Laboratoire de Biologie Cellulaire, Faculté des Sciences Biologiques, Complexe de Beaulieu, B.P. 25 A, 35031 Rennes, France.
Abstract:
The membrane proteins from Spiroplasma citri have been resolved into 16 components by SDS-polyacrylamide gel electrophoresis. By this technique it was also shown that the molecular weights of these proteins ranged from 13000 to 160 000. One of the proteins, which had an apparent molecular weight of 26 000 was the most abundant and represented more than 22% of total membrane protein. We have designated this protein spiralin. None of the proteins contained carbohydrate. Spiralin has been isolated by a procedure which involves removal of some membrane proteins with the neutral detergent Tween 20, selective solubilization of the Tween residue in DOC and fractionation of the DOC-soluble material by agarose-suspension electrophoresis. The homogeneity of spiralin was demonstrated by analytical polyacrylamide gel electrophoresis under different conditions and by crossed immunoelectrophoresis. Spiralin appeared to bind less DOC than the other membrane proteins of S. citri. This observation does not imply, however, that the binding of DOC to spiralin is weak. Spiralin was neither soluble in detergent-free buffers nor in Tween 20, which indicated that it is an intrinsic membrane protein. The amino-acid composition of spiralin was quite different from that of the membrane. Spiralin lacked methionine, histidine and tryptophan, and had a low content of glycine, leucine, tyrosine and phenylalanine, but a high content of threonine, alanine and valine.
Insights
Researchers isolated spiralin, a major intrinsic membrane protein from Spiroplasma citri. This abundant protein, comprising over 22% of total membrane protein, lacks carbohydrates and has a unique amino acid profile.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Spiroplasma citri is a helical, wall-less bacterium.
- Bacterial membrane proteins play crucial roles in cellular functions.
- Understanding membrane protein composition is key to elucidating bacterial physiology.
Purpose of the Study:
- To identify and characterize major membrane proteins of Spiroplasma citri.
- To isolate and determine the properties of the most abundant membrane protein.
- To investigate the nature and composition of Spiroplasma citri membrane proteins.
Main Methods:
- Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for protein separation and molecular weight determination.
- Detergent extraction (Tween 20, DOC) and agarose-suspension electrophoresis for protein isolation.
- Analytical polyacrylamide gel electrophoresis and crossed immunoelectrophoresis for purity assessment.
- Amino acid composition analysis.
Main Results:
- SDS-PAGE resolved 16 membrane protein components in Spiroplasma citri, with molecular weights ranging from 13,000 to 160,000.
- A protein designated spiralin, with an apparent molecular weight of 26,000, was identified as the most abundant component (over 22% of total membrane protein).
- Spiralin was isolated and confirmed as homogeneous, lacking carbohydrates, and classified as an intrinsic membrane protein due to its insolubility in detergent-free buffers and Tween 20.
- Amino acid analysis revealed spiralin has a distinct composition, lacking methionine, histidine, and tryptophan, with low glycine, leucine, tyrosine, and phenylalanine, but high threonine, alanine, and valine.
Conclusions:
- Spiralin is the predominant intrinsic membrane protein in Spiroplasma citri.
- The unique amino acid composition of spiralin suggests specialized functions within the bacterial membrane.
- Further research into spiralin's structure and function can provide insights into Spiroplasma citri biology and pathogenesis.
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